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    Aleksander Recnik currently works at the Department of Nanostructured Materials, Jožef Stefan Institute. Aleksander does research in Materials Chemistry, Nanotechnology and Solid-state Chemistry. Their most recent publication is 'Micro-sectoriality in hydrothermally grown ruby crystals: The internal structure of the boundaries of the growth sectors.'
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    Nina Daneu
    Taisia Alifirova
    Kristina Zagar
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    Matjaz Mazaj
    Ales Podgornik
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    In nature we find many examples of transformation faults, polytypic structures and epitaxial overgrowths of minerals and the reasons for their formation are poorly studied at the atomic scale and are generally not well understood. The main reasons are the dynamics and the complexity of growth conditions. Namely, during their growth, minerals are exposed to far more unpredictable thermodynamic conditions and diverse geochemical environments than the minerals synthesized in the laboratory. Their formation often involves a sequence of temperature dependent phase transformations, which are reflected in local structure and chemistry of the samples. To reconstruct a sequence of these unknown transient processes, a detailed structural and chemical characterization of the samples is of great help. Based on nanostructural investigations of the twin boundaries, precipitates and other topotaxial reactions we can not only reconstruct the dynamics of past geochemical processes, but also get a better insight into regional rock-forming and tectonic processes that were active during the crystal growth. The initial stages of phase transformations can be recognized by the formation of thermodynamically or chemically induced defects. Investigations of the initial stages of phase transformations is one of the central objectives of this project that offers possibilities for in-depth understanding the basic building principles of solids and fundamentals of phase transformations in minerals. Principal investigator: Dr. Nina Daneu Funding: National Research Agency (ARRS) Project duration: 2014-2017
    Research
    Research Items (142)
    Recent breakthrough of novel hierarchic materials, orchestrated through oriented attachment of crystal subunits, opened questions on what is the mechanism of their self-assembly. Using rutile-type TiO2, synthesized by hydrothermal reaction of Ti(IV)-butoxide in highly acidic aqueous medium, we uncovered the key processes controlling this nonclassical crystallization process. Formation of complex branched mesocrystals of rutile is accomplished by oriented assembly of precipitated fibers along the two low-energy planes, i.e. {110} and {101}, resulting in lateral attachment and twinning. Phase analysis of amorphous material enclosed in pockets between imperfectly assembled rutile fibers clearly shows harmonic ordering resembling that of the adjacent rutile structure. To our understanding this may be the first experimental evidence indicating the presence of electromagnetic force-fields that convey critical structural information through which oriented attachment of nanocrystals is made possible.
    The atomic scale structure and chemistry of (111) twins in MgAl2O4 spinel crystals from the Pinpyit locality near Mogok (Myanmar, formerly Burma) were analysed using complementary methods of transmission electron microscopy (TEM). To obtain a three-dimensional information on the atomic structure, the twin boundaries were investigated in crystallographic projections [110] and [112]. Using conventional electron diffraction and high-resolution TEM (HRTEM) analysis we have shown that (111) twins in spinel can be crystallographically described by 180° rotation of the oxygen sublattice normal to the twin composition plane. This operation generates a local hcp stacking in otherwise ccp lattice and maintains a regular sequence of kagome and mixed layers. In addition to rotation, no other translations are present in (111) twins in these spinel crystals. Chemical analysis of the twin boundary was performed by energy-dispersive X-ray spectroscopy (EDS) using a variable beam diameter (VBD) technique, which is perfectly suited for analysing chemical composition of twin boundaries on a sub-nm scale. The VBD/EDS measurements indicated that (111) twin boundary in spinel is Mg-deficient. Quantitative analyses of HRTEM (phase contrast) and HAADF-STEM (Z-contrast) images of (111) twin boundary have confirmed that Mg2+ ions are replaced with Be2+ ions in boundary tetrahedral sites. The Be-rich twin boundary structure is closely related to BeAl2O4 (chrysoberyl) and BeMg3Al8O16 (taaffeite) group of intermediate polysomatic minerals. Based on these results, we conclude that the formation of (111) twins in spinel is a preparatory stage of polytype/polysome formation (taaffeite) and is a result of thermodynamically favourable formation of hcp stacking due to Be incorporation on the {111} planes of the spinel structure in the nucleation stage of crystal growth. The twin structure grows as long as the surrounding geochemical conditions allow its formation. The incorporation of Be induces a 2Danisotropy and exaggerated growth of the crystal along the (111) twin boundary.
    We studied V-shaped twins of chrysoberyl (BeAl2O4) from Rio das Pratinhas pegmatites near Arataca in the Bahia state of Brazil. The local structure of the twin boundaries was determined using powder X-ray diffraction analysis (XRD), transmission electron microscopy (TEM) methods, and density functional theory (DFT) calculations. To provide the most reliable model for DFT and HRTEM simulations the structure of chrysoberyl was first refined in the orthorhombic space group 62 (Pmnb) with unit-cell parameters: a = 5.4825(1) Å, b = 9.4163(2) Å, and c = 4.4308(1) Å, with 0.5 at% of Fe3+ present on the Al(2) sites, suggesting an average composition of BeAl1.99Fe0.01O4. TEM study of V-shaped twins showed that the twin boundary lies in the (130) planes, and the angle measured between the crystal domains related by mirror twin operation is ~59.5°. Rigid structural model of (130) twin boundary in chrysoberyl was refined by DFT calculations, using a pseudo-potential method. The twin boundaries show local enrichment with Ti. Bulk chrysoberyl contains numerous nanosized TiO2 precipitates with a distorted rutile structure, following the orientation relationship of [001]Ch{120}Ch||[010]R{103}R. The increase of Ti at the twin boundaries and the formation of rutile-type TiO2 precipitates in bulk chrysoberyl suggest a transient Ti-exsolution that took place after the twin formation.
    Oriented rutile/hematite intergrowths from Mwinilunga in Zambia were investigated by electron microscopy methods in order to resolve the complex sequence of topotaxial reactions. The specimens are composed of up to several-centimeter-large euhedral hematite crystals covered by epitaxially grown reticulated rutile networks. Following a top-down analytical approach, the samples were studied from their macroscopic crystallographic features down to subnanometer-scale analysis of phase compositions and occurring interfaces. Already, a simple morphological analysis indicates that rutile and hematite are met near the <010>R{101}R||<001>H{110}H orientation relationship. However, a more detailed structural analysis of rutile/hematite interfaces using electron diffraction and high-resolution transmission electron microscopy (HRTEM) has shown that the actual relationship between the rutile and hosting hematite is in fact <010>R{401}R||<001>H{170}H. The intergrowth is dictated by the formation of {170}H|{401}R equilibrium interfaces leading to 12 possible directions of rutile exsolution within a hematite matrix and 144 different incidences between the intergrown rutile crystals. Analyzing the potential rutile–rutile interfaces, these could be classified into four classes: (1) non-crystallographic contacts at 60° and 120°, (2) {101} twins with incidence angles of 114.44° and their complementaries at 65.56°, (3) {301} twins at 54.44° with complementaries at 125.56° and (4) low-angle tilt boundaries at 174.44° and 5.56°. Except for non-crystallographic contacts, all other rutile–rutile interfaces were confirmed in Mwinilunga samples. Using HRTEM and high-angle annular dark-field scanning TEM methods combined with energy-dispersive X-ray spectroscopy, we identified remnants of ilmenite lamellae in the vicinity of rutile exsolutions, which were an important indication of the high-T formation of the primary ferrian-ilmenite crystals. Another type of exsolution process was observed in rutile crystals, where hematite precipitates topotaxially exsolved from Fe-rich parts of rutile through intermediate Guinier–Preston zones, characterized by tripling the {101} rutile reflections. Unlike rutile exsolutions in hematite, hematite exsolutions in rutile form {301}R|{030}H equilibrium interfaces. The overall composition of our samples indicates that the ratio between ilmenite and hematite in parent ferrian-ilmenite crystals was close to Ilm67–Hem33, typical for Fe–Ti rich differentiates of mafic magma. The presence of ilmenite lamellae indicates that the primary solid solution passed the miscibility gap at ~900 °C. Subsequent exsolution processes were triggered by surface oxidation of ferrous iron and remobilization of cations within the common oxygen sublattice. Based on nanostructural analysis of the samples, we identified three successive exsolution processes: (1) exsolution of ilmenite lamellae from the primary ferrian-ilmenite crystals, (2) exsolution of rutile lamellae from ilmenite and (3) exsolution of hematite precipitates from Fe-rich rutile lamellae. All observed topotaxial reactions appear to be a combined function of temperature and oxygen fugacity, fO2.
    Iron-cross twins of pyrite are well known among mineralogists, however it is quite surprising that the conditions of their formation remain unexplored. To address this question we studied pyrite twins from the Upper Permian silts of Mt. Katarina near Ljubljana (Slovenia), which represent one of the most typical geological environments for twinned pyrite. Mineralization of pyrite starts with a reduction of the primary red-coloured hematite-rich sediment by sulfide-rich fluids that penetrated the strata. A short period of magnetite crystallization is observed prior to pyrite crystallization, which indicates a gradual reduction process. Sulfur isotope analysis of pyrite shows an enrichment in δ34S, suggesting its origin from the neighbouring red-bed deposit. Other sulfides, such as chalcopyrite and galena, formed at the end of pyrite crystallization. Remnants of mineralizing fluids trapped at the interfaces between the inclusions and host pyrite show trace amounts of Pb and Cu, indicating their presence in the solutions throughout the period of pyrite crystallization. Electron microscopy and spectroscopy study of twin boundaries showed that interpenetration twinning is accomplished through a complex 3D intergrowth of primary {110} Cu-rich boundaries, and secondary {100} boundaries that are pure. We show that approximately one monolayer of Cu atoms is necessary to stabilize the {110} twin structure. When the source of Cu is interrupted, the two crystal domains continue to form {100} interfaces, that are more favorable for pure pyrite.
    We investigated the effects of dual doping of SnO2 varistor ceramics with 1 mol% CoO and different amounts of Nb2O5 (0.1 - 2 mol%) on the formation of twin boundaries, microstructure development and electrical properties. Nb2O5 addition shifts densification to higher temperatures (up to 1430 °C), producing microstructures composed of twinned SnO2 grains. Already 0.1 mol% Nb2O5 triggers a three-fold increase in growth rate via the diffusion induced grain boundary mobility (DIGM). At 0.5 mol % of Nb2O5 chemical equilibrium is achieved and SnO2 grains undergo normal grain growth. Electron back-scatter diffraction (EBSD) has shown that the prevailing type of twins is {101}. Cyclic twins are common. High-angle annular dark-filed scanning transmission electron microscopy (HAADF-STEM) image analysis revealed non-uniform segregation of Nb along the twin boundaries, indicating that they are not directly triggered by Nb2O5, but are a result of yet unexplained sequence of topotaxial replacement reactions. Energy dispersive spectroscopy (EDS) has shown that by dual doping of SnO2 with CoO and Nb2O5 the amount of Co dissolved in SnO2 grains is always ~4x lower compared to the amount of incorporated Nb and propose the following mechanism of tin out-diffusion: 6 Sn(IV)˟Sn(IV) ⇋ Sn(II)''Sn(IV) + Co(II)''Sn(IV) + 4 Nb(V)˙Sn(IV). Optimal electrical properties were achieved at 1 mol% Nb2O5 addition displaying high nonlinearity (α=50), high break-down voltage (571±12 V/mm) and low leakage current (IL = 4.2 µA). The addition of 2 mol% of Nb2O5 has an inhibiting effect on densification and SnO2 grain growth, resulting in a collapse of nonlinearity and increase of leakage current.
    This study explores the fine structural details of the boundaries between the growth micro-sectors in a ruby crystal grown hydrothermally on a nonsingularly oriented (01–1–2) seed. The samples were examined using IR-spectroscopy and HRTEM-analysis, demonstrating that these interfaces of the mi-cro-sectors serve as ‘traps’ for the OH-groups often observed in grown crystals. Counter to what has previously been reported, a significant proportion of these OH-groups is incorporated in ruby crystals in an orderly manner, forming diaspore-like layers growing epitaxially on the corundum (01–12) lattice planes. The tensions on the boundaries between the micro-sectors result to local increase of an internal pressure, making diaspore-like phase is stable. The assumption is made, that the mechanism discussed in the article can explain the occurrence of OH-groups in the structure of nominally anhydrous minerals, such as MgSiO3 (akimotoite) which is structurally similar to corundum.
    Quarz ist bereits ein Meister der Zwillingsbildung und der tektonischen Verzerrung. Wenn man jedoch die Komplexität verzerrter Hyalophan-Kristalle betrachtet, kann man nur ehrfürchtig den Hut ziehen.Also, tief durchatmen mit diesem 2.Teil des Artikels, bevor man in dieses komplexe Gebiet einsteigt. In den folgenden Beschreibungen ist es empfehlenswert, jeweils die Realkristalle und deren idealisierte Zeichnungen parallel zu betrachten.
    Clinoptilolite-rich tuff (Z) enriched with Fe(III) was studied in the removal of phosphate ions present in aqueous medium at pH = 6.5. Fe(III) modification was performed by a simple wet impregnation giving the product (FeZ) with about 18 wt% Fe. Transmission electron microscopy showed the presence of a flaky Fe(III) amorphous precipitate on the clinoptilolite sheets and a preserved clinoptilolite crystallinity. The modification increased the specific surface area from 28.6 to 140.3 m2/g. FeZ effectively adsorbed phosphate , the removal rate at 298 K varying from 86% to 42.5% (for Co = 50 mg/l and Co = 400 mg/l). The sorption isotherms were in accord with the Langmuir model, giving for the Langmuir constant (RL) values in the range 0–1 that are characteristic of a favourable adsorption. The data for adsorption kinetics were best described by the pseudo-second-order model suggesting chemisorption as the phosphate sorp-tion mechanism. Intra-particle diffusion was present in the adsorption, but it was not the rate-limiting step. A 31P static spin-echo mapping nuclear magnetic resonance (NMR) measurement was performed for studying the phosphate–FeZ interaction. The results showed that the phosphate adsorption on FeZ proceeds through electrostatic interactions and covalent bonding, the latter being more pronounced.
    Infolge einer einzigartigen geologischen Entwicklung bildeten sich im Bereich des Zagradski Potok mehrere subparallele Gänge mit alpinotyper Mineralbildung, die über einen Zeitraum von 60 Jahren ca. eine Tonne von Hyalophan-Stufen hervorbrachten. Die Bildung der Gänge erfolgte langsam und ohne große Turbulenzen, wodurch das Wachstum von hervorragenden langgestreckten und komplexen Kristallen begünstigt wurde. Dadurch bildeten sich auch einige verschiedene Hyalophan-Zwillinge mit flächenreichem Habitus. Diese Lokalität übertrifft alle anderen Hyalophan-Vorkommen bei weitem. Die Mehrzahl der Hyalophan-Kristalle ist nach dem Baveno-Manebacher oder KarlsbadGesetz verzwillingt, wobei es komplexe Kombinationen von Baveno-ManebacherDrillingen, -Vierlingen und doppelten Baveno-Manebacher-Zwillingen gibt. Zu den Begleitmineralien gehören herausragende Fadenquarze und eine Vielzahl anderer für die alpinotypen Gänge typischen Mineralien. Hyalophan wird von der IMA (International Mineralogical Association), die für neue Mineralien und Mineralnamen zuständig ist, als eigenständige Spezies angesehen und ist das Bindeglied zwischen Orthoklas und dem Celsian-Endglied. Nach der Definition muss Orthoklas, die Niedertemperatur- Varietät des Kalifeldspats, mindestens 5 % des Celsian-Endglieds beinhalten, damit man ihn Hyalophan nennen darf. Die Kristalle von Zagradski Potok enthalten aber bis zu 40% des Celsian-Endglieds und liegen daher sehr nahe an der theoretischen Zusammensetzung des Hyalophans.
    The (ZnO)kIn2O3 system is interesting for applications in the fields of thermoelectrics and opto-electronics. In this study we resolve the complex homologous phase evolution with increasing temperature in polycrystalline ceramics for k = 5, 11 and 18 and its influence on the microstructural development and thermoelectric properties. The phase formation at temperatures above 1000 °C is influenced by the local ZnO-to-In2O3 ratio in the starting-powder mixture. While the Zn5In2O8 equilibrium phase for k = 5 is formed directly after sintering at 1200 °C, the formation of the k = 11 and k = 18 equilibrium phases proceeds at higher temperatures by diffusion between the initially formed phases, the lower k Zn5In2O8/Zn7In2O10 and the higher k ZnkIn2O(k+3) (9 < k < ∞). Such phase formation affects the sintering and grain growth, and consequently, with the degree of structural and compositional homogeneity, also the thermoelectric characteristics of the (ZnO)k In2O3 ceramics.
    The potential possibility of intergrowth of two bulk crystals to single crystal was demonstrated on the example of beryl, Be3Al2Si6O18, growing under hydrothermal conditions. The result has practical importance because it allows to increase the yield of useful product on a single growth cycle. The fine structure and composition of the matter of the area adjacent to the splicing boundary was investigated. It was demonstrated that the influence of the intergrowths border of two crystals spliced in parallel is entirely analogous to the affect of a twin boundary. This analogy extends as well on the specific morphology of the growth front generated by the boundary as on the growth velocity of the surfaces adjacent to the boundary that is increasing in 3÷10 times. In addition we show that the spliced crystals orientate each other in parallel. The assumption on the nature of the driving forces of such impact was made. We also suggest assumption about the nature of this orientational forces.
    We investigated the high-temperature thermoelectric properties of Ga:ZnO bulk compounds, synthesized using a simple and scalable solid-state process. The effects of a low gallium content (x ≤ 0.04 in Zn1-xGaxO1+x/2) on the structural features and electrical/thermal properties are reviewed. Transmission electron microscopy analyses showed that 2D, nonperiodic defects had formed from a doping content as low as x = 0.01 Ga. The structural description of these nanoscale interfaces is, for the first time, carefully investigated in such low-Ga-content samples by HAADF-STEM analyses combined with structural modeling. It was found that the formation of head-to-head inversion twin (h-IT) boundaries and tail-to tail inversion boundaries (t-IB) in the bulk compounds is responsible for strong phonon scattering, while maintaining relatively good electrical conductivity and thereby enhancing the thermoelectric properties. The absolute value of the Seebeck coefficient decreases abruptly from 475 μV/K for x = 0 down to 60 μV/K for x = 0.005 at 350 K. At the same time, the electrical resistivity drops from 1 ohm cm for x = 0 to 1.7 × 10(-3) ohm cm for x = 0.005. For higher Ga additions (x > 0.01), the increase in electrical resistivity is likely linked to the formation of interface defects at a larger extent in the wurtzite structure. The thermal conductivity also drops sharply with the increase in the Ga content from ∼33 W/m K for x = 0 to ∼8 for x = 0.04 at 350 K. This study is progress toward the synthesis of other thermoelectric materials where nanoscale interfaces in bulk compounds provide tremendous opportunities for further enhancing both the phonon scattering and the overall figure of merit.
    In the search for suitable scaffold materials for tissue regeneration, silk fibroin has become one of the most promising candidates due to its biocompatibility and good physical properties. To facilitate bone formation in osteochondral defects, it is often combined with a bone promoting additive. Here we demonstrate using HRTEM analysis how the release of Ca2+ ions from bioactive glass or Ca-salts results in the reduction of β-sheet domain size that effectively controls a scaffold's properties, such as degradation and mechanical stiffness. We show that these changes already occur in silk fibroin solution prior to scaffold preparation and are caused by a decrease in zeta potential that forces fibroin molecules into tighter packing resulting in higher scaffold crystallinity, smaller β-sheet domains and higher interconnectivity. The reduction of β-sheet domains improves the elastic modulus and allows faster degradation despite the higher crystallinity. Ca2+ was also shown to be beneficial to the formation of hydroxy-apatite sheets on the fibroin surface.
    The mechanism of ilmenite–rutile transformation during oxidation of natural ilmenite crystal was studied at elevated temperatures in air. The progress of oxidation with annealing time was studied in the temperature range between 600 and 900 C. 2.5 mm cubes were cut from the single Mn-ilmenite crystal in two special orientations, [001]ILM and [1-10]ILM, that allowed determination of crystallographic relations among the reaction products. Using X-ray diffractometry, energy-dispersive spectroscopy, and electron microscopy (SEM, TEM) techniques, we determined that the ilmenite to rutile and hematite transformation is triggered by surface oxidation of divalent cations (Fe, Mn) from the starting ilmenite and their crystallization in the form of hematite and bixbyite on the surface of the single crystal. Surface oxidation and outdiffusion of Fe2+ and Mn2+ ions opens paths for exsolution of rutile within the pseudo-hexagonal oxygen sublattice of the parent ilmenite, following simple topotaxial orientation relationship [001]RUT {010}RUT || [210]ILM {001}ILM. With this transformation, new channels for fast out-diffusion of divalent cations to the oxidation surface are opened along the c-axis of the rutile structure. The volume difference of the reaction products causes cracking of the single crystal, which opens additional free surfaces for accelerated oxidation. The results of this study contribute to better understanding of the recrystallization processes during pre-oxidation of ilmenite.
    Project - Atomic-scale studies of initial stages of phase transformations in minerals
    Update
    Project update – publications:
    2016:
    Vanja Jordan, Uroš Javornik, Janez Plavec, Aleš Podgornik, Aleksander Rečnik. Self-assembly of multilevel branched rutile-type TiO2 structures via oriented lateral and twin attachment. Scientific reports 6 (2016) 24216:1-13, https://www.researchgate.net/publication/301198006
    Jonathan P. Winterstein, Meltem Sezen, Aleksander Rečnik, Barry C. Carter. Electron microscopy observations of the spinel-forming reaction using MgO nanocubes on Al2O3 substrates. Journal of Materials Science 51/1 (2016) 144-157. https://www.researchgate.net/publication/281615545
    Nadežda Stanković, Aleksander Rečnik, Nina Daneu. Topotaxial reactions during oxidation of ilmenite single crystal. Journal of Materials Science 51/2 (2016) 958-968. https://www.researchgate.net/publication/284725417
    Aleksander Rečnik, Janez Zavašnik, Lei Jin Andrea Čobić, Nina Daneu. On the origin of »iron-cross« twins of pyrite from Mt. Katarina, Slovenia, Mineralogical Magazine 80/6 (2016) in…
    The morphology evolution and associated topotactic relations between MgO nanocubes deposited on electron-transparent Al2O3 substrates were monitored after repeated high-temperature ex situ heat treatments. Owing to the well-defined morphology of MgO smoke cubes and flat basal-plane-oriented substrate, the initial orientation relationship is constrained to be {100}MgO || (0001)sapphire. In this geometry, only one rotational degree of freedom is allowed for MgO particles, and hence, a full set of coincident site lattices are formed, providing the opportunity to examine thermodynamic and kinetic processes and track competing surface and bulk ion-diffusion mechanisms during spinel formation. Crystallographic orientation relationships (ORs) between the sapphire (Al2O3) substrate, the magnesia (MgO) smoke nanoparticles, and the MgAl2O4 spinel reaction products were studied before and after annealing in the temperature range between 1000 and 1100 C. The ORs adopted between the different pairs of materials were studied using single (0001)-oriented sapphire crystals pre-thinned for transmission electron microscopy (TEM) observations; the spinel/sapphire interface was further investigated on cross-section TEM specimens prepared from bulk samples using the focused ion-beam technique. At temperatures below ~1050 C, the prevailing OR is <110> {111}spinel || <10-10> {0001}sapphire; whereas above that temperature <110> {100}spinel || <10-10> {0001} sapphire becomes more common. With the increasing temperature also the morphology of the spinel product is transformed from hexahedral to octahedral. The different ORs and microstructures appear to depend on the reaction temperature and result in different dominating diffusion mechanisms.
    Understanding growth mechanisms usually leads to the successful preparation of a targeted microstructure. However, the large number of parameters that influence the shape and the size of nanostructures often make it difficult to predict the outcome. We investigated the growth of wurtzite-type ZnO by closely following such a multistage process. We associated the diverse morphology of the precipitated crystals, prepared under the same hydrothermal conditions, to the differences in the transient crystallization processes during the precipitation. By altering the pH of the suspension after the precipitation, we gain control over the resulting morphology of the ZnO and show how to grow identical crystallites with different shapes and crystal sizes. Here we report, for the first time, on how ZnO platelets grow in a certain Zn2+/OH− ratio along the basal and one of the prismatic directions to form sphalerites with very high surface area. We also offer an explanation as to how sphere-like hierarchical structures composed of plate- or rod-like ZnO crystals form through self-assembly driven processes.
    In MINERALIEN-Welt 1/2014 wurde die kleine Mineralienbörse von Kreševo nahe Sarajevo vorgestellt. Eine Börse, die bisher wohl nur von einigen wenigen Händlern aus Slowenien und auch Italien frequentiert wird und Sammlern in Mitteleuropa generell kaum bekannt sein dürfte, aber von der lokalen Bevölkerung gut aufgenommen wird. Auch über die Mineralien der Region des Zentralbosnischen Schiefergebirges ist nur wenig bekannt, obwohl dieses Gebiet mit der Hyalophan-Lokalität von Busovača eine Weltfundstelle vorzuweisen hat (ŽORŽ 1996). Die ehemals bedeutende Fundstelle für die weltbesten Hyalophane (siehe dazu auch REČNIK 2009) ist heute als erloschen zu betrachten, da hier ein Staudamm errichtet wurde und die Stollen und Klüfte mit Hyalophan unter Wasser liegen. Aus dem Übertagebereich sind Vorkommen von Hyalophan bisher nicht bekannt geworden. In diesem Beitrag werden zunächst die Mineralien aus den Alpinen Klüften von Busovaca vorgestellt, während in weiteren Folgen die Funde von Kresovo und die Geschichte der außergewöhnlichen Hyalophane präsentiert werden.
    Silk fibroin as a natural biopolymer is often used for scaffold for bone regeneration as a composite with inorganic osteostimulative material, such as hydroxyapatite, calcium phosphate, diopside or bioactive glass, where the inorganic part serve to promote osteostimulation and to improve scaffolds mechanical properties toughness and hardness. Those inorganic parts are rich in Ca2+ that can be dissolved out of it, especially from highly soluble bioactive glass, and can change the scaffolds properties. In the present work SF/nanoparticulate BG composite scaffolds were prepared and the impact of BG and its released Ca2+ ions on the protein structure, crystallinity and molecular mass were examined and related to scaffolds mechanical and degradation properties.
    Erstmals 1990 machten Fluoritfunde in der Nähe der Ortschaften Potok und Osojnik nördlich des Berges Blegos die Fachwelt auf ein außergewöhnliches Vorkommen aufmerksam. In den folgenden Jahren konnten außerordentlich attraktive Stufen mit violettem und grünem Fluorit, Antimonit, Valentinit, Chalkostibit, Quarz, sovie gelbem Calcit geborgen werden. Zu den Höhepunkten zählen zweifellos die mit Quarz überzuckerten Fluorit-Stufen verschiedener Generationen.
    Question - Why does grain size increase with increasing dopant concentration in case of Fe doped BaTiO3 ceramics ?
    Answer
    Do you observe (111) twins in BaTiO3 grains? They could form on doping with 3+ cations and trigger exaggerated grain growth. Check you microstructures for twins.
    Spectroscopic and microscopic (particularly HRTEM) techniques were used to investigate the origin of the colour of natural blue Zn-carbonate (smithsonite). Blue smithsonite is rich in copper, but substitution of zinc cations by copper cations, as proposed in the past for the origin of the colour, is questionable considering the absence of anhydrous divalent copper carbonates in nature. In this work, optical microscopy, SEM-EDS, XRD and laser micro-Raman could not resolve distinct phases either than Zn-carbonate, while NIR spectra excluded known chromophore Cu-hydroxycarbonate minerals. HRTEM studies however could clearly resolve nano-sized (3-7 nm) Cu-rich inclusions (specifically Si/Ca/Cu/As-rich inclusions of at least one phase), which are organised in bands with no topotaxial relation to bulk smithsonite. Electron-beam sensitivity of the samples, even at low electron current densities, did not allow the exact identification of the inclusions. However, it can be safely suggested, for the first time in the literature, that they are the cause of the blue colour in smithsonite.
    Meine erste Begegnung mit den wunderschönen Amethysten von Mexiko fand im Jahr 1992 statt, als ich den Mineralienhändler Marco Schreier in Renningen während meines Studiums in Stuttgart besuchte. Es war ein glücklicher Zufall, dass er gerade kurz zuvor eine bergfrische Sendung von Amethysten aus Mexiko erhalten hatte. Die Regale in seinem Laden waren gefüllt mit herrlich gefärbten Stufen in einer Qualität, wie ich sie noch nie zuvor gesehen hatte.
    Die Uran-Lagerstätte Zirovski vrh liegt innerhalb des gleichnamigen Höhenrückens, ca. 30 km westlich von Ljubljana, zwischen den Bächen Brebovščica an der nordöstlichen und Račeva an der südwestlichen Flanke. Im nordöstlichen Teil dieser Region gibt es in den Konglomeraten und Sandsteinen ein reiches Uranvorkommen mit zahlreichen alpinotypen Quarz-Calcit-Klüften. Die Lagerstätte wurde im Jahr 1960 in der Folge intensiver Erkundungen auf Uranerze entdeckt. Neben einer Vielzahl primärer und sekundärer Uranmineralien stammen aus der Umgebung von Zirovski vrh Quarze mit den verschiedensten Einschlüssen, herrliche Rauchquarze, perfekt kristallisierte Calcite, der hier seltene Brookit und Gips, der sich auch heute noch bildet.
    Several methods with solid and dissolved reactants were investigated as possible routes for synthesis of single-phase valentinite Sb2O3. The methods are based on simple chemical reaction between SbCl3 and NaOH. The method with solid state reactants was established on self-propagating room temperature reaction (SPRT), while wet syntheses were based on the same chemical reaction, and performed in either distilled water or absolute ethanol. The prepared powders were characterized by X-ray powder diffraction, scanning electron microscopy and field emission scanning electron microscopy, high-resolution transmission electron microscopy, selected area electron diffraction (SAED) and UV/vis diffuse reflectance spectroscopy. SPRT and aqueous solution syntheses resulted in single-phase valentinite Sb2O3, but with significantly different morphologies. In the case of SPRT method the obtained powder contains well crystallized prismatic shaped submicronic particles, with hexagonal or lozenge basis typical for valentinite crystal structure, while aqueous solution synthesis resulted in powder containing micronic agglomerates. The ethanolic solution synthesis product was Sb2O3 with cubic senarmontite as predominant phase and traces of orthorhombic valentinite. It was confirmed that not only the aggregate state, but also the choice of solvent has a great influence on the structural and optical characteristics of synthesized Sb2O3 powders.
    Question - Can I find out the crystallographic orientation relationship between substrate (cubic) and film (HCP) theoretically?
    Answer
    Hi Aditi Thanki,
    If you have structurally related sublattices (111) planes of ccp structure usually matches (0001) planes of the hcp structure. See, e.g. structurally related pairs like sphalerite-wurtzite, diamond-lonsdaleite, spinel-chrysoberyl (or taaffeite), etc.
    Cheers,
    Alex
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    Se(IV) and Se(VI) anions are the dominant species of Se existing in aqueous systems. In this study, the iron(III)-modified natural zeolitic tuff (Fe-CLI) from the Serbian deposit Zlatokop has been investigated as an adsorbent for the Se oxyanions. Fe-CLI shows adsorption activity for both Se(IV) and Se(VI) which decreases with increasing pH. The adsorption capacity of Fe-CLI is found to be higher for Se(IV) than for Se(VI). Kinetics data follow the pseudo-second-order model and the obtained parameters k indicate that the rates of adsorption and desorption are higher for Se(VI). Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) analyses reveal that Se is bound at the zeolite surface forming not only the Se-O-Fe but also Se-O-Si bonds. The adsorption mechanism depends of the type of oxo ions. Samples of zeolitic tuff which contain Se were tested as soil supplements for the cultivation of Pleurotus ostreatus mushrooms. The fungus adsorbed the inorganic Se from zeolitic tuff transforming it to a more valuable organically bound form. (C) 2014 Published by Elsevier Inc.
    Question - How beneficial a correct indexing of non-centrosymmetric crystal by EBSD would be?
    Answer
    Definitely agree!
    Under kinematic diffraction conditions the difference in the intensities for -g and +g reflections must be visible due to their different structure factors. This has been shown for thin noncentrosymmetric crystals in TEM, and should work for EBSD, too.
    In ZnO we have shown that triangular etch-pits point to the positive direction of the polar c-axis; EBSD though, would be a much more elegant solution, because it also shows the general orientation of the crystal grains.
    Alex
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    With carefully planned synthesis procedure we can obtain samples of PtCu3 alloyed nanoparticles embedded in graphitized carbon support with the identical platinum, copper and carbon composition, particle dispersion and size distribution yet with different degree of structural ordering. Systematic stability study, employing RDE, ICP-MS, HR-TEM and IL-TEM measurements reveals that partially ordered sample consistently exhibits higher ORR activity and Cu content upon dealloying and electrochemical degradation treatments. For the first time we show a direct proof that ordered structure increases PtCu3 electrocatalyst stability for ORR activity. Together with the formation of Pt-skin [1] this could have a groundbreaking impact on future rational design of active and stable platinum alloyed oxygen reduction reaction electrocatalysts. Figure 1: Schematic representation of a cross-section of the ordered PtCu3/C sample.
    We present a novel scale-up sol-gel synthesis to produce 20 g batches of highly active and stable carbon supported PtCu nanoparticles as a cathode material in low temperature fuel cell. We confirm the presence of ordered intermetallic phase underneath the multilayered Pt-skin together with firm embedment of nanoparticles in the carbon matrix.
    Mežica is the largest lead and zinc ore deposit in Slovenia. Mined for over 350 years; it is one of the world's richest wulfenite deposits. Most of the major mineralogical collections and museums in the world have at least one specimen from this classic occurrence. And the locality is far from exhausted; many fine specimens have been collected in recent years.
    In this study the performance enhancement effect of structural ordering for the oxygen reduction reaction (ORR) is systematically studied. Two samples of PtCu3 nanoparticles embedded on a graphitic carbon support are carefully prepared with identical initial composition, particle dispersion and size distribution, yet with different degrees of structural ordering. Thus we can eliminate all coinciding effects and unambiguously relate the improved activity for the ORR and more importantly the enhanced stability to the ordered nanostructure. Interestingly, the electrochemically induced, morphological changes are common to both ordered and disordered samples. The observed effect could have a groundbreaking impact on the future directions in the rational design of active and stable platinum alloyed ORR catalysts.
    ZnFe2O4 was prepared by a soft mechanochemical route from two starting combinations of powders: (1) Zn(OH)2/α-Fe2O3 and (2) Zn(OH)2/Fe(OH)3 mixed in a planetary ball mill. The mechanochemical treatment provoked reaction leading to the formation of the ZnFe2O4 spinel phase that was monitored by XRD, TEM, IR and Raman spectroscopy. The spinel phase was first observed after 4 h of milling and its formation was completed after 18 h in both the cases of starting precursors. The synthesized ZnFe2O4 has a nanocrystalline structure with a crystallite size of about 20.3 and 17.6 nm, for the cases (1) and (2), respectively. In the far-infrared reflectivity spectra are seen four active modes. Raman spectra suggest an existence of mixed spinel structure in the obtained nanosamples. In order to confirm phase formation and cation arrangement, Mössbauer measurements were done. Estimated degree of inversion is about 0.58 for both starting mixtures. The magnetic properties of the prepared ZnFe2O4 powders were also studied. The results show that the samples have a typical superparamagnetic-like behavior at room temperature. Higher values of magnetization in the case of samples obtained with starting mixture (2) suggest somewhat higher degree of cation inversion.
    This study provides an overview of the recent experiments employing methods that analyse, systematically, series of analytical spectra acquired either in nanobeam mode in a transmission electron microscope or using elemental mapping in a scanning transmission electron microscope. A general framework is presented that describes how best to analyse series of such spectra to quantify the areal density of atoms contained within a very thin layer of a matrix material, as, for example, appropriate to measure grain boundary segregation. We show that a systematic quantification of spectra as a function of area size illuminated by the electron beam eliminates the large systematic errors inherent in simpler approaches based on spatial difference methods, integration of compositional profiles acquired with highly focused nanoprobes or simple repeats of such measurements. Our method has been successfully applied to study dopant segregation to inversion domain boundaries in ZnO, to quantify the thicknesses of sub-nm thin layers during epitaxial growth by molecular beam epitaxy of (In)GaAs and to prove the absence of gettering of dopants at Σ = 3{111} grain boundaries in Si, with a precision <1 atom/nm2 in all these cases.
    Die Region um Litija kann auf eine lange Bergbaugeschichte zurückblicken. Ihre Anfänge gehen in die Eisenzeit zurück; davon zeugen früheste Spuren einer menschlichen Ansiedlung auf dem Gipfel des Berges Sitarjevec oberhalb von Litija sowie Funde von Situlen (lat. 'Eimer'), die im Zuge archäologischer Ausgrabungen einige Kilometer von Lithia entfernt in Yace gelangen. In dieser Zeit baute man hauptsächlich reiche Limoniterze aus dem Eisernen Hut der Lagerstätte ab. Die Gewinnung von Eisenerzen hielt an bis zum Beginn des 16. Jahrhunderts; in der Folge konzentrierte man sich auf Blei- und Quecksilbererze. Für Mineraliensammler von Interesse sind für diese Fundstelle vor allem schöne Cerussit-Kristalle.
    We studied the atomic structure and the chemical composition of (101)-type rutile (TiO2) twins from Diamantina in Brazil by electron microscopy methods to resolve the mechanism of their formation. The twin boundaries were studied in two perpendicular orientations to reveal their 3D structure. The pres-ence of a precursor phase, such as Al-rich hydroxylian pseudorutile (HPR; kleberite), during the initial stages of the crystallization appears to be the necessary condition for the formation of (101) twins of rutile at this locality. The precursor with a tivanite-type structure serves as a substrate for the topotaxial crystallization of rutile. Depending on the initial crystallization pattern the rutile can grow either as a single crystal or as a twin. During the progressive crystallization of the rutile Al-rich oxyhydroxide (diaspore, α-AlOOH) clusters are concentrated at the center of the precursor where they are pinned to the twin boundary as the precursor is fully recrystallized into rutile. At the increased temperatures the remaining diaspore precipitates are converted to corundum (α-Al2O3), while the two crystal domains continue to grow in the (101) twin orientation. In addition to the primary (101) twin, series of secondary {101} twins are formed to accommodate the residual tensile stress caused by the diaspore-to-corundum transformation. Based on the observed corundum-rutile [0001]C (1120)C || [010]R (101)R and ilmenite-rutile [0001]I (1100)I || [010]R (301)R crystallographic relations a unified mechanism of the genesis of the {101} and {301} reticulated sagenite twin clusters is proposed.
    We studied the influence of Cu-addition on the first precipitate, near-amorphous mackinawite-type FeS, and subsequent phase transformations in the Fe-S system. Despite many studies on the formation and phase transition of Fe-sulphides, the structure and physical properties of this first precipitate are still not well explained. To investigate the reaction products, iron and copper chlorides were mixed in different ratios together with sulphur and diethanolamine, and sonicated to achieve efficient mixing; already at this stage the first FeS precipitate was formed. TEM investigation of Cu-doped mackinawite-like FeS showed enhanced crystallinity accompanied with expansion of the unit cell along the c-axis, proportional to the amount of Cu adsorbed between the (001) layers of the mackinawite structure. The subsequent solvothermal treatment and sulphurization of undoped FeS resulted in formation of pyrite, at low doping Cu-rich mackinawite and cubic (Fe,Cu)S with a sphalerite-type structure were formed, while at higher Cu concentrations the end-products were chalcopyrite and bornite, corresponding to the initial amount of Cu in the reagents.
    Nano spinel ferrites MFe2O4 (M= Ni, Mn, Zn) were obtained by soft mechanochemical synthesis in a planetary ball mill. The appropriate mixture of oxide and hydroxide powders was used as initial compounds. All of this mixture of powders was mechanically activated, uniaxial pressed and sintered at 1100°C/2h. The phase composition of the powders and sintered samples were analyzed by XRD and Raman spectroscopy. Morphologies were examined by SEM. In this study, the AC-conductivity and DC-resistivity of sintered samples of MFe2O4 (M= Ni, Mn, Zn) ferrites were measured at different frequencies and at room temperature. The values of the electrical conductivities show an increase with increasing temperature, which indicated the semiconducting behavior of the studied ferrites. The conduction phenomenon of the investigated samples could be explained on the basis of hopping model. The complex impedance spectroscopy analysis was used to study the effect of grain and grain boundary on the electrical properties of all three obtained ferrites.
    Materials providing additional crystallographic information on orientation relationships of observed twin boundaries, stacking faults and epitaxial layers in magnetite and maghemite nanocrystals, based on FFT analysis and nano-diffraction data
    The origin of growth defects and epitaxial layers in nanocrystalline magnetite (Fe3O4) and its oxidation product, maghemite (gamma-Fe2O3), was studied. In magnetite, two types of planar defects are identified, (111) spinel-law twin boundaries and (110) stacking faults (SF). The twinning in magnetite is related to magnetic-field-assisted self-assembly and the growth of octahedral nanocrystals throughout their crystallization period. Simple contact twins of crystals sharing common octahedral faces, or even plate-like twins develop when two adjoined crystals continue their growth as a unit. Crystallographically, twinned domains are related by 180° rotation about the [111]-axis and with the (111) plane as the interface, producing local hcp stacking in the oxygen sub-lattice. SFs are present in both single and twinned magnetite crystals, where they are pinned to (111) twin boundaries and are present only in one domain. The displacement vector corresponding to the observed translation is R(SF) = 1/4[110], pointing normal to the (110) plane of the SF. After the thermal treatment at 250°C both types of planar defects are retained. In addition to planar defects, originating from magnetite, we identified a new formation of few-nanometers-thick epitaxial layers, of a hexagonal Fe(III)-oxide–hydroxide, feroxyhyte (d-FeOOH), covering the octahedral faces of the maghemite crystals. The crystallographic relationship between maghemite and feroxyhyte is described by [110](222)mag || [010](002)fer.
    The present work is the first comprehensive study of mineralogy of the world's second largest mercury mine Idria. In the first chapter the readers are acquainted with the history of mining and its relation to mineralogy. Mineralogy is explained in terms of geological processes that were active during the formation of the ore deposit. Among these, hydrocarbons present in the host rocks play a very important role during crystallization. The central part of the book is dedicated to the main mineral of the ore deposit, cinnabar. It occurs in a variety of crystal forms, of which the most special are lateral interpenetration twins. The book is written for a broad readership, and will be interesting for geologists, mineralogist and crystallographers, as well as for those interested in the history of mineral collecting in Idria.
    Microstructure development in ZnO ceramics with Bi4Ti3O12 (BIT) additions was studied in dependence of sintering temperature, inversion boundary (IBs) nucleation, heating rate and doping with transition metal oxides (NiO, MnO2 and Co3O4). We demonstrated that one of the essential conditions for homogeneous microstructure development in this system is rapid release and efficient distribution of TiO2, necessary for the formation of Ti-rich (tail-to-tail) IBs in ZnO grains. This can be achieved via the so-called shock-sintering procedure described in this article. Immediate decomposition of BIT to TiO2-rich Bi2O3 liquid phase above 1200°C leads to nucleation of ZnO grains with IBs. Exploiting the growth of ZnO grains with IBs, microstructure development can be easily controlled via the IB-induced grain growth mechanism, previously described in SnO2-doped and Sb2O3-doped ZnO. In contrast to conventional sintering, where erratic nucleation of IBs leads to bimodal grain size distribution, shock-sintering sintering regime produces microstructures with uniform coarse-grain sizes, required for low-voltage varistor ceramics.
    In this study the catalytic activity of Na-rich and MO-containing natural clinoptilolite (MO – nanoparticles of NiO, ZnO, or Cu2O) was studied in the pyrolysis of hardwood lignin. The clinoptilolite samples exhibit different catalytic activities which depend mainly on the type of the nano-oxide. The presence of nano-oxides did not affect the porosity of the clinoptilolite framework but influenced its acidity. However, it seems that acidity of the lattice did not influence the catalytic activity of the clinoptilolite in the pyrolisis of hardwood lignin. The number of Lewis acid sites increased significantly for the ZnO- and Cu2O-containing clinoptilolite whereas for the NiO-sample it did not change appreciably in comparison to the parent zeolite. The amount of phenols in the as-produced bio-oil varies from 39% for ZnO-clinoptilolite, 43% for Na-rich clinoptilolite, to 50 and 54% for Cu2O- and NiO-containing samples, respectively. The highest yield of phenols obtained in the presence of NiO-containing clinoptilolite is ascribed to a synergetic interaction of the clinoptilolite lattice and nano-NiO particles.
    Titanates are suitable for many applications such as oxygen sensing and tunable HTS (high temperature superconducting) microwave filters. The potential advantages of the nanostructured forms have been however scarcely explored compared to other oxides. In this work, the structural and electrical properties of individual iron-doped strontium titanate nanotubes (Fe:SrTiO3) grown by electrophoretic deposition (EPD) were assessed for the first time, showing high stability and reproducibility. This result paves the way to further development of more complex titanate-based devices, as for instance nanostructured oxygen STFO sensors. From experimental data, it was concluded that the polycrystalline form of Fe:SrTiO3 nanotubes is the major limitation to attain high photoconductivity gains when exposed to UV-light.
    Applications involving transparent conducting films (TCFs), such as flat-panel displays and touch screens technologies, are dominated by indium-tin-oxide (ITO). Increasing prices of indium in hand with weaknesses of ITO films make a strong argument for alternative TCFs with competitive characteristics and lower price. Here we demonstrate the potential of highly oriented zinc oxide (ZnO) films grown on glass substrates under low-temperature hydrothermal (HT) conditions at 90 °C from aqueous solutions of Zn-nitrate and Na-citrate. Formation of a continuous ZnO seed-layer with proper thickness, grain size, connectivity, and orientation of seed-grains on glass is shown to be essential to achieve conditions for the growth of highly oriented (0001), smooth, transparent, and conductive ZnO films according to the spatially confined oriented growth (SCOG) mechanism. The film grown on homogeneous seed-layer with grain size of about 20 nm showed optical transmittance of up to 82% and relatively low resistivity for undoped ZnO ceramic in order of few 100 Ω sq−1. Such characteristics are explained by highly oriented crystalline texture and high coalescence of ZnO crystals in these films.
    NiFe2O4 and ZnFe2O4 ferrites have been prepared by soft mechanochemical synthesis. The formation of spinel phase and crystal structure of sintered powders were analyzed by X-ray diffraction, Raman spectroscopy, and transmission microscopy. In order to confirm phase formation and cation arrangement, Mössbauer measurements were done. Investigation of the magnetization as a function of magnetic field confirms an expected change of the degree of inversion in the spinel structure with the sintering. The electrical DC/resistivity/conductivity was measured in the temperature range of 298-423 K. Impedance spectroscopy was performed in the wide frequency range (100 Hz-10 MHz) at different temperatures.
    Recent studies of {110} twin boundaries in natural pyrite (FeS2) indicated that twinning is triggered by the presence of Cu during crystal growth. Here we investigated the formation sequence of Fe-sulphides produced by the chemical vapor transport (CVT) method at 600°C in an evacuated quartz tube using Fe- and Cu-halides and elementary S as the reaction precursors. Depending on the mobility of elements different Fe-sulphides crystallized through gradually decreasing temperature zones. At the higher temperature zones, where metal ions are present in abundance, the main reaction product is FeS in form of pyrrhotite-3 T. The main characteristic of this pyrrhotite is the presence of {111} layers cubic FeS coherently intergrown with the {0001} layers of the hosting hexagonal FeS. While the hosting structure corresponds to distorted troilite (nickeline-type structure) with octahedrally coordinated Fe2+ ions, iron in cubic FeS either remains in octahedral coordination (rocksalt-type structure) or is translated to tetrahedral interstices (sphalerite-type structure). HRTEM analysis suggests that Fe2+ ions in the cubic sequences remain in the octahedral sites, suggesting a new, cubic close-packed, rocksalt-type structure of FeS. Cubic FeS shows a high density of twins and SFs in the {111} planes. Pyrite crystallized in the temperature zone between 500 and 450 °C, where the concentration of metal ions is depleted. With a decreasing temperature its morphology changes from {111}→{210}→{100}. Doping with copper did not result in twinning of pyrite, suggesting that different thermodynamic conditions are present in the natural environment. Using the natural seed crystal we showed that the twin boundaries are continued across the interface into the CVT grown epitaxial pyrite, whereas the marcasite-type SFs terminate at the interface.
    Barium strontium titanate was obtained by hydrothermal treatment of barium strontium titanate citric precursor solution, previously prepared by complex polymerization method. The thermally induced phase evolution was followed at various temperatures up to 800 °C using thermogravimetric and differential thermal analysis, X-ray diffraction analysis, and Raman spectroscopy. Microstructural characterization of barium strontium titanate powders was performed by scanning and transmission electron microscopy. The proposed synthesis route has been proven as a better and faster method for barium strontium titanate powder preparation as compared to the conventional complex polymerization route. The method was found efficient for production of low agglomerated, fine, nanosized barium strontium titanate powder with well defined stoichiometry, and sub-micron particle size. The results of structural and microstructural characterization showed the complete crystallization of carbonate-free barium strontium titanate powder at 700 °C with an average size of crystallites below 50 nm.
    Nickel ferrite, NiFe2O4 has been prepared by a soft mechanochemical route from mixture of (1) Ni(OH)2 and α-Fe2O3 and (2) Ni(OH)2 and Fe(OH)3 powders in a planetary ball mill for varying duration. Soft mechanochemical reaction leading to formation of the NiFe2O4 spinel phase was followed by X-ray diffraction, Raman and infrared spectroscopy, TGA, scanning and transmission microscopy. The spinel phase formation was first observed after 4 h of milling and its formation was completed after 25 h in the both cases. The synthesized NiFe2O4 ferrite has a nanocrystalline structure with a crystallite size of about 20 and 10 nm respectively for the cases (1) and (2). The final grain size in the system (1) is about twice as large as that in the system (2), what is a consequence of different reaction paths in these two processing routes. There are five Raman and four IR active modes. Mössbauer spectroscopy studies implied on the possible cation distribution between the tetrahedral and octahedral sites in formed NiFe2O4 spinel structure. We were able to estimate the degree of inversion at most 0.82 in the case (1) and 0.66 in the case (2).
    A recent study of (111) twins in MgAl 2 O 4 spinel crystals from Mogok (Burma) implied that twinning could be triggered by the presence of Be during crystal growth. Here we demonstrate that twinning in spinel is in fact chemically induced and is not a consequence of an accidental attachment of crystals. The growth conditions were reproduced in a tube furnace at 1200 uC by liquid-phase assisted reaction of Al 2 O 3 and MgO with the addition of BeO, while PbF 2 was used as melt-forming agent. BeO does not only cause abundant {111} twinning of spinel, but also complex topotaxial overgrowths of BeMg 3 Al 8 O 16 taaffeite when the concentration of BeO exceeds 12.5 mol%. A HRTEM study of the spinel–taaffeite interface confirmed the following epitaxial relationship: [11 ¯ 0]?{111} sp I[112 ¯ 0]?{0001} taf . The basic structural unit, observed on (111) twin boundary in spinel (i.e. Be 2+ replacing for Mg 2+ on the interfacial tetrahedral interstices), is identical to hexagonal close-packed (hcp) sequences observed in ternary taaffeite compounds, suggesting that twinning is probably a preparatory stage of polytype formation. The formation {111} twins in spinel is explained in the context of twin-induced exaggerated grain growth mechanism. This phenomenon can be exploited for the production of spinel crystals with complex morphologies.
    Platinum copper alloy nanoparticle catalysts supported on graphitized carbon with and without partial crystal ordering were synthesized and tested for oxygen reduction and methanol oxidation reaction for potential use in direct methanol fuel cells and proton exchange membrane fuel cells. The activity enhancement by at least a factor of 2 is possible when Pm-3m phase is present in the nanoparticle with respect to the pure Fm-3m phase. A significance of Pt-skin type catalysts concept is explained for lowering the platinum content.
    There is an increasing technological demand for magnetic nanocrystals with special morphologies and controlled sizes. Several approaches are used for the synthesis of magnetite crystals with irregular or octahedral shapes; however, the room-temperature synthesis of nanocrystals with specific morphologies is not yet established. Here, we describe the synthesis of magnetite crystals (100–300 nm) at a relatively low temperature (~70 °C) from organic precursors, including Fe(II) oxalate or Fe(II) sulfate, and study the effects of ethylene glycol and tetraethylene glycol on the final physical and chemical properties of the crystals. The magnetite crystals formed from different precursor materials (sulfate or oxalate green rust) show specific morphological and textural features. We show that octahedral magnetite crystals can be produced from Fe(II) oxalate via a simple co-precipitation process. Using different kinds and amounts of polyols, various types of particle morphologies and nanocrystal textures can be produced, including hexagonal-shaped clusters of elongated crystals and porous and solid, large, rounded polycrystalline aggregates.
    Flat panel display technology seems to be an ever-expanding field developing into a multibillion dollar market. A set of technical solutions involve a transparent conducting film (TCF) that is today still dominated by indium-tin-oxide (ITO). In a race to find alternatives that would avoid the indium pitfalls, mainly due to its increasing price and limited natural availablity, replacement materials have been extensively investigated. This work demonstrates that by exploiting basic principles of crystal growth in geometrically constrained conditions, zinc oxide (ZnO) could easily be utilized for this purpose. ZnO layers were grown on inexpensive glass substrates via low-temperature citrate-assisted hydrothermal (HT) method. It was shown that in the nucleation stage the crystal growth can be efficiently controlled by spatially confined oriented growth (SCOG) mechanism to produce smooth and dense (0001) oriented polycrystalline ZnO films with superb optical properties. Our products show optical transparency of 82% and surprisingly low sheet resistance for undoped ZnO, only in the order of few 100 Ω sq−1. We believe that a very high degree of self-organization between the ZnO crystals in our polycrystalline films grown under controlled SCOG conditions is main reason for the highest so far reported transparency to conductivity ratio for undoped ZnO thin film ceramics.
    Nanocrystalline iron sulfides form in diverse anoxic environments where sulfide is present and dissolved iron is available. The initial precipitate is either referred to as nanocrystalline mackinawite (FeS) or amorphous FeS. This material may then transform to greigite (Fe3S4) and, finally, to pyrite (FeS2). Iron sulfide nanocrystals also form and convert inside the cells of some magnetotactic bacteria. We synthesized iron sulfide from hydrous solutions near room temperature and studied its properties and conversion to mackinawite and greigite. The results were used for obtaining a better understanding of the structure of the initial precipitate, and for interpreting the similarities and differences between the mechanisms of iron sulfide formation and conversions in anoxic sediments and in magnetotactic bacteria.
    Lanthanum nickelate (LNO) is a perovskite oxide material with metallic conductivity in a wide temperature range which makes it suitable for application as electrode material for thin films. In this paper LNO thin films were prepared by polymerizable complex method from the diluted citrate solutions. Precursor solutions were spin coated onto Si-substrates with amorphous layer of SiO2 . Deposited layers were thermally treated from the substrate side with low heating rate (1 °/min) up to 700 °C and finally annealed for 10 hours. Results of AFM and FESEM showed that films are very smooth (Ra = 4 nm), dense, crack-free and with large square-shaped grains (170 nm). According to FESEM and TEM results the obtained four-layered film was only 65 nm thin. EBSD and XRD analyses confirmed polycrystalline microstructure of the films without preferential orientation. It was concluded that the presence of SiO 2 layer on Si substrate prevents epitaxial or oriented growth of LNO.
    The morphology, size and growth of anatase TiO2 crystals have been studied using a transmission electron microscope (TEM) and X-ray powder diffraction (XRD). The material was prepared by hydrothermal synthesis from aqueous suspension of amorphous TiO2 at temperatures from 40 to 200 °C and times up to 200 h. The size of the crystals increased with the synthesis temperature and time from around 6 to 20 nm. From high-resolution TEM images shape of crystals was reconstructed. It was found that in the initial stages of growth anatase crystals adopt uncommon morphologies, which were combination of basic crystallographic forms typical for anatase, however these forms were not developed symmetrically as determined by the surface energy values for these particular planes. The asymmetry and abnormal growth into rod-like and wedge-shaped crystals was most probably a consequence of inhomogeneous supply of building material due to high competition among numerous (relatively) rapidly growing randomly oriented nanocrystals. This leads to highly non-equilibrium conditions in the initial growth stages. Close to equilibrium at higher temperatures and times all crystals tend to adopt simple bipyramidal morphology.
    Phase transformations in minerals are important indicators of geochemical and thermodynamic changes during crystal growth. Initial stages of phase transformations can be recognized by the formation of thermodynamically or chemically induced planar defects, such as twin, antiphase, or inversion boundaries in the affected crystals. Based on the principles of crystal chemistry, some early scientists suggested that the atomic structure of the twin boundary must be related to the existing polymorphic modification of the major phase. The confirmation of this hypothesis was not possible until the development of modern electron microscopy techniques, which enabled a direct insight into the local structure and chemistry of twin boundaries at the atomic scale. Our studies of twins and other translational defects in minerals have shown that their formation is chemically induced by specific dopants that stabilize the particular polytypic structure. Inherent anisotropy imposed by the chemically induced transformation fault (e.g. growth twin) causes exaggerated growth of the crystal parallel to the fault plane as long as geochemical and thermodynamic conditions favour the forma-tion of faulted stacking. These initial growth stages dictated by the growth of the chemically induced fault are clearly reflected in the final morphology of the crystals and can be recognized by the so-called twin-plane re-entrant angles and the additional symmetry elements that can be observed on such crystals. Because of commonly complex geochemical conditions minerals incorporate an assortment of foreign elements that are present during crystal growth, only one of these elements, however is responsible for the faulted stacking (e.g. twinning). In order to identify the elements that trigger twinning in minerals we developed new techniques that enable atomic-scale determination of the interfacial crystal chemistry. The investigations of twinning in minerals represents one of the fundamental scientific challenges that offers possibilities for true understanding of the basic building principles of solids and fundamentals of phase trans-formations in minerals.
    Secondary carbonate precipitates (dripstones) formed on concrete surfaces in four different environments--Mediterranean and continental open-space and indoor environments (inside a building and in a karstic cave)--were studied. The fabric of dripstones depends upon water supply, pH of mother solution and carbonate-resulting precipitation rate. Very low δ(13)C (average-28.2‰) and δ(18)O (average-18.4‰) values showed a strong positive correlation, typical for carbonate precipitated by rapid dissolution of CO(2) in a highly alkaline solution and consequent disequilibrium precipitation of CaCO(3). The main source of carbon is atmospheric or biogenic CO(2) in the poorly ventilated karstic cave, which is reflected in even lower δ(13)C values. Statistical analysis of δ(13)C and δ(18)O values of the four groups of samples showed that the governing factor of isotope fractionation is not the temperature, but rather the precipitation rate.
    Nanocrystalline iron sulfides form in diverse anoxic environments. The initial precipitate is commonly referred to as nanocrystalline mackinawite (FeS) or amorphous FeS. In order to better understand the structure of the initial precipitate and its conversion to mackinawite and greigite (Fe3S4), we studied synthetic iron sulfide samples that were precipitated from hydrous solutions near room temperature. The transformation of precipitated FeS was followed in both aqueous and dry aging experiments using X-ray powder diffraction (XRD) and scanning and transmission electron microscopy (SEM/TEM) and selected-area electron diffraction (SAED).
    In ceramic materials, special boundaries play the key role in crystal growth. They introduce an abrupt structural and chemical anisotropy, which is readily reflected in an unusual microstructure evolution, whereas their local structure affects the physical properties of polycrystalline materials. These effects, however, can be exploited to tailor the electronic and optical properties of the materials, as demonstrated in this review. The presented topic is related to a preparatory stage of phase transformations, manifested through the evolution of chemically induced structural faults. In non-centrosymmetric structure of ZnO, inversion boundaries (IBs) are the most common type of planar faults that is triggered by the addition of the specific IB-forming dopants (Sb 2O 3, SnO 2, TiO 2). In addition to conventional TEM techniques, new methods were developed to resolve crystallography and atomic-scale chemistry of IBs. The absolute orientation of the polar c-axes on both sides of an IB was determined by micro-diffraction, providing the most reliable identification of crystal polarity in non-centrosymmetric crystals. To determine sub-monolayer quantities of dopants on the IB, we developed a special technique of analytical electron microscopy using concentric electron probe (CEP) in EDS or EELS mode, providing more accurate and precise results than any other technique. Knowing the local crystal chemistry of IBs, we were able to design experiments to identify their formation mechanism. IBs nucleate in the early stage of grain growth as a dopant-rich topotaxial 2D reaction product on Zn-terminated surfaces of ZnO grains.
    Die Umgebung von Cerknica ist schon seit Jahrhunderten aufgrund von Funden wasserklarer Quarz-Kristalle, die man wegen ihres schönen Glanzes und ihres kurzprismatischen Habitus 'Zirknitzer-Diamanten' genannt hat, bestens bekannt. Der hohe Glanz, der für Quarz nicht gerade typisch ist, scheint Folge des Kristallwachstums aus kohlenwasserstoffenreichen Losungen zu sein. Neben diesen sogenannten 'Diamanten' findet man in der Umgebung von Cerknica noch eine Reihe von zepter-, pagoden- und fensterartigen sowie 'dachförmigen' Kristallen. Manche Quarze sind durchsichtig und rauch ig gefärbt. Sie können aber auch ganz schwarz sein und weisen dann zahlre iche Bitumen-Einschlüsse auf. Es gibt auch Quarze mit Fluideinschluss-Libellen und mit Einschlüssen von Dolomit-Kristallen.
    Tin selenides SnSe X (x=1,2) were synthesized from tin and selenium powder precursors by high-energy milling in the planetary ball mill Pulverisette 6 (Fritsch, Germany). The orthorhombic tin selenide SnSe and the hexagonal tin diselenide SnSe 2 phases were formed after 4 min and 5 min of milling, respectively. Specific surface area of both selenides increased with increasing time of mechanochemical synthesis. The particle size distribution analysis demonstrated that the synthesized products contain agglomerated selenide particles consisting of numerous idiomorphic tin selenide crystals, measuring from 2 to more than 100 nm in diameter, which were also documented by TEM. UV-Vis spectrophotometry confirmed that tin selenide particles do not behave as quantum dots.
    In semiconducting materials special boundaries play the key role in crystal growth. They introduce an abrupt structural and chemical anisotropy, which is readily reflected in an unusual microstructure evolution, whereas their local structure affects the physical properties of semiconducting materials. These effects, however, can be exploited to tailor the electronic and optical properties of the materials, as demonstrated in this review. The presented topic fits in the field of preparatory stage of phase transformations, manifested through evolution of chemically induced structural faults. In the noncentrosymmetric structure of ZnO, inversion boundaries (IBs) are the most common type of planar faults that can be triggered by the addition of specific spinel-forming dopants (Sb2O3, SnO2, TiO2). In addition to conventional HRTEM techniques several new methods were developed to resolve crystallography and atomic-scale chemistry of IBs. The absolute orientation of the polar c-axes on both sides of the IB was determined by a novel quantitative microdiffraction method, providing a reliable identification of crystal polarity in noncentrosymmetric crystals. To determine sub-monolayer quantities of dopants on the IB, we developed a special technique of analytical electron microscopy using concentric electron probe (CEP) in EDS or EELS mode, providing more accurate and precise results than any other available technique. Knowing the local crystal chemistry of IBs we were able to design experiments to identify their formation mechanism. IBs nucleate in the early stage of grain growth as a dopant-rich topotaxial 2D reaction product on Zn-terminated surfaces of ZnO grains. Soon after their nucleation, ZnO is epitaxially grown on the inherent 2D phase in an inverted orientation, which effectively starts to dictate anisotropic growth of the infected crystallite. In very short time the grains with IBs dominate the entire microstructure in ZnO ceramics via IB-induced exaggerated grain growth mechanism. This phenomenon was used to design physical properties of ZnO-based varistor ceramics, whereas the bottom-up approach demonstrated here provides the basic tool for microstructural engineering of functional materials in virtually any system that is prone to formation of special boundaries.
    Es gibt sicher nicht viele Mineraliensammler, die noch nichts über die vom Mt. Malosa in Malawi stammenden, herrlichen Aegirine gehört haben, die mit glänzendem Rauchquarz und weiteren Pegmatitmineralien vergesellschaftet sind. Größere Mengen an Stufen tauchten Ende der 1990er-Jahre auf dem Mineralienmarkt auf, als der italienische Forscher und Mineraliensucher Mario Picciani von Lilongwe aus das systematische Sammeln von Mineralien am Berg Malosa organisierte. In den letzten zehn Jahren wurde dadurch der Mt. Malosa als Weltklasse-Fundort für attraktive Vergesellschaftungen von Syenitpegmatit-Mineralien bekannt. Die Reportage nimmt uns mit auf die abenteuerliche Reise zum Mt. Malosa im Juli 2010.
    Manganese ferrite, MnFe2O4 have been prepared by a soft mechanochemical route from mixture of (a) Mn(OH)2 and α-Fe2O3 and (b) Mn(OH)2 and Fe(OH)3 powders in a planetary ball mill. The mixture was activated for varying duration. Soft mechanochemical reaction leading to formation of the MnFe2O4 spinel phase was followed by X-ray diffraction, Raman spectroscopy, scanning and transmission microscopy and magnetization measurements. The spinel phase formation was first observed after 12h of milling and its formation was completed after 25h in both cases. The synthesized MnFe2O4 ferrite has a nanocrystalline structure with a crystallite size of about 40 and 50nm respectively for cases (a) and (b). There are five Raman active modes. Measurements after 25h of milling show magnetization values of 70.4emu/g and 71.1emu/g respectively for cases (a) and (b). In order to understand better the whole process of phase formation, Mössbauer measurements were done.
    Zinc oxide nanopowders were synthesized by the sol–gel method from an ethanol solution of zinc acetate dihydrate. Detailed structural and microstructural investigations were carried out using x-ray diffraction, Raman spectroscopy, thermogravimetric and differential thermal analyses, as well as high-resolution transmission electron microscopy (TEM) and field-emission scanning electron microscopy. The intermediate compound of the reaction was layered zinc hydroxide acetate that further transforms into hexagonally shaped ZnO crystalline nanoplates (dm = 4 nm), which aggregate into larger spherical particles. According to the TEM analysis the ZnO nanoparticles were self-assembled into larger particles with the same orientation, i.e. aligned lattice planes of the particles. A further solvothermal treatment resulted in hexagonal, prismatic ZnO mesocrystals.
    In this work, we report on the integration of individual BaTiO(3) nanorods into simple circuit architectures. Polycrystalline BaTiO(3) nanorods were synthesized by electrophoretic deposition (EPD) of barium titanate sol into aluminium oxide (AAO) templates and subsequent annealing. Transmission electron microscopy (TEM) observations revealed the presence of slabs of hexagonal polymorphs intergrown within cubic grains, resulting from the local reducing atmosphere during the thermal treatment. Electrical measurements performed on individual BaTiO(3) nanorods revealed resistivity values between 10 and 100 Ω cm, which is in good agreement with typical values reported in the past for oxygen-deficient barium titanate films. Consequently the presence of oxygen vacancies in their structure was indirectly validated. Some of these nanorods were tested as proof-of-concept humidity sensors. They showed reproducible responses towards different moisture concentrations, demonstrating that individual BaTiO(3) nanorods may be integrated in complex circuit architectures with functional capacities.
    We have studied the formation of BiMnO3 (BMO) nanocrystalline perovskite powder produced by high-energy milling of the constituent oxides. The crystal structure and the amount of crystalline and amorphous phases in the powder as a function of the milling time were determined with XRPD using Rietveld refinement. BMO perovskite formed directly from highly activated nano-sized constituent oxides after 240min of milling and subsequently grew during prolonged milling. The morphology, structure, and chemical composition of the powder were investigated by SEM and TEM. A clear ferromagnetic transition was observed at T C ~66K for a sample milled for 240min and increased with milling time. The magnetic hysteresis behavior is similar to that of a soft ferromagnet. The magnetic properties of the obtained BMO powders were found to change as a function of milling time in a manner consistent with variations in the nanocomposite microstructure. KeywordsMilling–X-ray methods–TEM–Magnetic properties–Bismuth manganite–Nanocomposites
    The present communication reports an interesting observation on stepwise development of crystallinity along with change in elemental composition of the HAp crystals, precipitated on SS 316L substrates (4mm×5mm×1mm) by biomimetic route. The SS 316L substrates were incubated up to 6 days in simulated body fluid (SBF) at 37°C with a periodic replacement of freshly prepared SBF at 48h intervals. X ray diffraction (XRD) analysis of coated substrates revealed phase pure hydroxyapatite (HAp) as the only phase present in the coating. Transmission electron microscopy (TEM) images of the coating showed a gradual transformation of core shell type spherical HAp crystal into elongated forms over a period of 6 days of incubation of SS 316L substrate in SBF. The elemental composition of the deposited HAp phase was also changed with increase in exposure time of SS 316L to SBF as indicated by the energy dispersive spectra (EDS) of coated substrates.
    Nanoparticles of NiO, ZnO and Cu2O crystallize when the Ni-, Zn- and Cu-exchanged natural clinoptilolite, respectively, are dehydrated by heating in air at 550°C. The dehydration of Mn-exchanged clinoptilolite does not lead to the crystallization of manganese oxide but affects the crystallinity of the host clinoptilolite lattice, which becomes amorphous. The NiO, ZnO and Cu2O nanoparticles are found to be randomly dispersed in the clinoptilolite matrix. The particle size varies from 2 to 5nm and exceeds the aperture of the clinoptilolite channel (approximately 0.4nm), suggesting that the crystallization of the oxide phases takes place on the surfaces of clinoptilolite microcrystals.
    The structure of the unusual `hemimorphic' wulfenite crystals from the Mežica mine (Slovenia) was refined in the noncentrosymmetric space group I̅4 using a Pb/Mo exchange disorder model with the approximate composition Pb0.94Mo0.06MoO4. Pb atoms in the 2b positions are substituted by Mo at about 12%. The crystal is shown to be twinned by inversion. Hemimorphism may result from short-range chemical ordering of the metal atoms at the 2b positions.
    Mechanochemical synthesis of tin diselenide, SnSe2, was performed by high-energy milling of tin and selenium powder in a planetary ball mill. The mechanosynthesized product was characterized by X-ray diffraction, 119SnMAS NMR and 119Sn Mössbauer spectroscopy, which confirmed the presence of the hexagonal SnSe2 phase after 100 min of milling. The size and morphology of tin diselenide particles were studied by specific surface area measurements, and transmission electron microscopy. The specific surface area of powders was found to increase with increasing time of mechanochemical synthesis. Electron diffraction revealed reflections that correspond to hexagonal SnSe2 modification. TEM observations show that the mechanochemical preparation route results in the formation of nanosized thick barrel-shaped SnSe2platelets. SnSe2nanoparticles show good absorption in the visible region of the UV-Vis optical spectrum and they evidence direct and indirect types of transitions in the lattice.
    An electron-microscopy investigation was performed on BaTiO3 nanorods that were processed by sol–gel electrophoretic deposition (EPD) into anodic aluminium oxide (AAO) membranes. The BaTiO3 nanorods grown within the template membranes had diameters ranging from 150 to 200nm, with an average length of 10–50μm. By using various electron-microscopy techniques we showed that the processed BaTiO3 nanorods were homogeneous in their chemical composition. The BaTiO3 nanorods were always polycrystalline and were composed of well-crystallized, defect-free, pseudo-cubic BaTiO3 grains, ranging from 10 to 30nm. No intergranular phases were observed between the BaTiO3 grains. A low-temperature hexagonal polymorph that is coherently intergrown with the BaTiO3 perovskite matrix was also observed as a minor phase. When annealing the AAO templates containing the BaTiO3 sol in an oxygen atmosphere the presence of the hexagonal polymorph was diminished.
    ZnO grain-growth kinetics was studied in the ZnO+1 mol% Bi2O3 system with the addition of 0.1 and 0.5 mol% SnO2 between 950° and 1300°C. It was found that inversion boundaries (IBs) are the major factor influencing the ZnO grain growth in this system. After the nucleation of the IBs in the ZnO grains, these grains grow exaggeratedly and anisotropically in the direction of the inherent IB, causing a plate-like development of these grains. At 950°C, the IB-induced grain-growth mechanism is characterized by a low grain-growth exponent (N) of 2, from 15 to 240 min of sintering. At higher temperatures (1100°–1300°C), the IB-induced grain growth is finished already after approximately 15 min and the N-value is even lower, ranging from 1.7 (1100°C) to 1.4 (1300°C), with the apparent energy for ZnO grain growth of ∼148 kJ/mol. After the impingement of the plate-like ZnO grains with IBs, further growth follows the Ostwald-ripening mechanism, which is an incomparably slower growth process. In this growth stage, the N-value increases to ∼3.5 and the apparent grain-growth energy is increased to ∼353 kJ/mol (1100°–1300°C). After long sintering times, the samples reach an equilibrium microstructure comprised of only ZnO grains with IBs. During this stage, the grain growth is virtually stopped, which is reflected in very high N-values of 20 and more.
    Any future fusion reactor will require a structurally sound vacuum chamber that is able to withstand the attack of hydrogen produced in the transmutation reactions, while at the same time exhibiting the rapid decay of any induced radioactivity. However, the Eurofer '97 steel, which has already been chosen for the DEMO reactor, although possessing reduced activation, remains very susceptible to hydrogen. In this study we have looked at the effectiveness of thin, TiAlN coatings with respect to the permeability of hydrogen at 400 °C. Our results reveal that the coating forms a columnar structure, with evidence of epitaxy at the substrate–coating interface, and that this coating can produce a permeation reduction factor for hydrogen of up to 20,000. This is substantially higher than any other coating reported for this type of steel. Furthermore, the relatively low costs associated with such films and the breadth of knowledge that already exists about their characteristics suggest that such a combination of a TiAlN coating and the Eurofer '97 steel could be a very promising material for reactor technologies.
    A novel approach to tailoring the microstructure and electrical characteristics of ZnO-based varistor ceramics via inversion-boundary (IB) induced grain growth ZnO-based varistors with exceptional current-voltage (I-U) nonlinearity are widely used in the over-voltage protection of electrical equipment and devices at voltages ranging from a few volts to several hundred kilo-volts. Their breakdown voltage is strongly influenced by the average ZnO grain size: a coarse-grained microstructure results in a low breakdown voltage for the ceramics, while a fine-grained microstructure is required for a high breakdown voltage. The grain size in high-voltage varistor ceramics is controlled by the addition of a spinel-forming additive, typically Sb2O3 . The concept of grain-growth inhibition due to the reduced grain-boundary mobility caused by the pinning effect of the spinel particles largely defines the composition of the ZnO-based varistor ceramics with additions of 7 to 10 wt.% of varistor dopants to the ZnO. Spinel-forming dopants such as Sb2O3 , TiO2 and SnO2 also result in the formation of inversion boundaries (IBs) in the ZnO grains. We have identified an IB-induced grain-growth mechanism which primarily controls the microstructure development, while the role of the spinel is subordinated. This understanding enabled us to prepare varistor ceramics with excellent I-U nonlinearity and breakdown voltages, ranging from 120V/mm to 350V/mm with the amount of varistor dopants added to the ZnO reduced to only about 3 wt.%.
    Quasicrystalline (i-phase) Ti–Zr–Ni samples were obtained using the melt-spinning technique, where the Ti/Zr ratio ranged from 1 to 3, while the Ni content remained nearly constant, varying between 17 and 20at. %. We replaced the Zr with 3 and 5at. % of Cu in order to test the i-phase-forming ability of the samples, which were all subsequently hydrided from the gas phase at 45bar and 300°C for 1000min. We then made XRD analyses of the as-spun and loaded samples in order to determine the influence of the composition and the absorbed hydrogen content on the cell parameter of the i-phase. An almost linear decrease of this parameter with the ([Ti]+[Cu])/[Zr] ratio was found for the as-prepared and hydrided samples, where the slope of the linear fit is preserved after hydrogenation, but with about 6% higher values due to the expansion of the quasilattice. XPS analyses of the melt-spun i-Ti45Zr35Ni17Cu3 revealed an oxide-layer thickness of 4nm. A TEM investigation revealed that the size of the i-phase grains on the wheel side of the ribbon was approximately five times smaller than on the bright side, as a result of the higher cooling rate and the resulting faster nucleation rate.
    We report on an unusual crystallization phenomenon that results in the self-assembly of sub-micron tubules of crystalline SrTiO3. The deposition of the tubular structures was done in the pores of anodized aluminum oxide templates by the electrophoretic deposition of SrTiO3 sols and subsequent annealing. Homogeneous nucleation inside the pores produces a critical number of crystallites leading to their self-organization when the nanocrystals reach sizes that equal the mean free distances between the nuclei. Due to steric constraints the crystals start to organize in order to most efficiently fill the available surface of the pore walls. This process leads to the formation of domains containing a large number of idiomorphic SrTiO3 nano-cubes that are self-aligned into almost perfect cube-on-cube and cube-to-wall registry, which makes up the walls of the tubules. The described mechanism shows the ability of nanocrystals with well defined morphologies to adapt spatial constraints and self-organize into desired geometries.
    X-ray powder-diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), infrared spectroscopy (IR), thermogravimetry (TG) and mass spectroscopy (MS) were performed to investigate the composition and the crystal structure of tetra-barium di-niobate (V) Ba 4Nb2O9. The TG, MS and IR studies revealed that the compound is a hydrated oxycarbonate. Assuming that the carbonate stoichiometrically replaces oxygen, the composition of the low-temperature α-modification, obtained by slow cooling from 1100 °C, corresponds to Ba4Nb2O8.8(CO3) 0.2·0.1H2O, while the quenched high-temperature γ-modification has the Ba4Nb2O 8.42(CO3)0.58·0.38H2O composition. The α-phase has a composite incommensurately modulated structure consisting of two mutually interacting [Ba]∞ and the [(Nb,□)O3]∞ subsystems. The composite modulated crystal structure of the α-phase can be described with the lattice parameters a=10.2688(1) , c=2.82426(8) , q=0.66774(2)c (*) and a superspace group R3̄m(00γ)0s. The HRTEM analysis demonstrates the nanoscale twinning of the trigonal domains parallel to the {1 0 0} crystallographic planes. The twinning introduces a one-dimensional disorder into the [(Nb,□)O3]∞ subsystem, which results in an average P6̄2c crystal structure of the α-phase. Possible places for the carbonate group in the structure are discussed using a comparison with other hexagonal perovskite-based oxycarbonates.
    Multilayers formed from weak polyions of polyallylamine (PAH) and polyacrylic acid (PAA), possessing ion-exchangeable carboxylic groups were used to bind the metal cations within the film. By subsequent wet chemical reaction process of the incor-porated metal ions, pure zinc sulfide (ZnS) with a narrow size distribution was formed wit-hin the PEMs. The size and concentration of the inorganic nanoparticles in polyion matrix were controlled by the concentration of metal – binding carboxylic acid groups as determi-ned by the multilayer assembly pH. Furthermore, the metal cation loading and reaction met-hodology could be repeatedly cycled to increase the size and volume density of the nano-particles. Furthermore, the polyelectrolyte multilayer films were used as templates for the ceramic (TiO2) thin film fabrication with a modified sol-gel reaction. Since the multilayer assembly is performed from the polyion aqueous solutions, the multilayers contain some water that, after infiltration of the organometallic precursor, enables in-situ reaction of hydrolysis and condensation reaction. After calcination, nanocrystalline TiO2 thin films with thickness, controllable by the number of the polyion layers in the matrix, were formed. With the in-situ synthesis approach of inorganic nanstructures in polyelectrolyte multilayer matrix, the ability of obtaining the control over the film thickness and size of the inorganic particles has enabled the tuning of the optical properties of as fabricated inorganic-organic composite films, as well as nanocrystalline ceramic films.
    A novel experimental setup for studying the initial stages of formation and growth of MgAl2O4 spinel on an α-Al2O3 substrate has been devised. Nanometer-scale cubes of MgO formed by Mg combustion were deposited on (0001)-oriented single crystals of alumina by holding the specimen near burning Mg metal. Some of the Al2O3 was pre-thinned to electron transparency and annealed to remove the specimen preparation damage before depositing MgO particles; while cross-section specimens were prepared by focused ion beam from bulk specimens. Spinel-forming reactions were carried out in a furnace at temperatures from 1000 to 1100 °C. Our experiments were designed to acquire some insights into how selection of surfaces and temperatures influence the interaction of oxide nanoparticles with substrates, a scenario applicable for a number of technologies.
    The Mo–Ni–O powders were electrodeposited from ammonium sulfate containing electrolytes with dif-ferent Mo/Ni ion concentration ratios. The phase composition of these powders was investigated using TEM, EDS and XRD analysis. The TEM analysis showed that two types of particles were present in the pow-ders: amorphous and crystalline. For crystalline particles it was found that two phases, MoO3 and MoNi4 prevail in all powders, while the NiO phase was detected in the powder electrodeposited at Mo/Ni = 0.3/1. These findings are in good agreement with our previous results where MoO3 , MoNi4 and NiMoO4 phases were detected in the recrystallized Mo–Ni–O powders. In this work we discovered that the NiMoO4 phase was formed by solid state reaction between NiO and MoO3 at elevated temperature.
    Idrija (früher auch „Idria") zählt bei den Mineraliensammlern zu den bedeutendsten Fundstellen für schöne Cinnabarit-Kristalle und gediegenes Quecksilber. Der Legende nach hat ein Böttcher (Fassbinder) im Jahre 1490 in der Nähe der heutigen Kirche der Heiligen Dreifaltigkeit sein neues Fass im Wasser tränken wollen und es deswegen über Nacht an eine nahe Quelle gebracht. Früh am Morgen fand er auf dem Boden des Fasses eine merkwürdige schwere, silberne Flüssigkeit. Seinen Fund brachte er zu einem Goldschmied nach Škofja Loka (Bischofslaak), der ihn gleich als Quecksilber erkannte. Die Nachricht über den sensationellen Fund verbreitete sich rasch und so kamen Bergleute aus Friaul, Kärnten und Tirol nach ldrija. In dem damals nahezu unbesiedelten Tal entwickelte sich im 16. Jahrhundert eine Bergbaustadt, die nach dem Quecksilber (lat. Hydrargyrum) den Namen Hydria bekam. Mit seiner 500-jährigen Geschichte reiht sich das Bergwerk ldrija in die weltbekannten Sehenswürdigkeiten der Natur- und Technikgeschichte ein.
    Ultrathin PZT film was prepared using a chemical solution deposition method from polymeric citrate precursors. The PZT solution was spin-coated on an amorphous silica layer formed on a Si(100) substrate. The films were thermally treated from the substrate side with a low heating rate (1°/min) up to 700 °C and finally annealed for 10 h. Ultrathin PZT films without microstructural instability were prepared in spite of high temperature and long annealing time. AFM and HRTEM investigations revealed the formation of a well-developed dense microstructure consisting of spherical crystallites (4–7 nm). Low roughness (2.2 nm) of a ∼26 nm thick layer was obtained for a two-layered PZT film. The grazing incidence X-ray diffraction (GIXRD) measurements confirmed the polycrystalline structure of ultrathin PZT films. Also, GIXRD and electron energy dispersive X-ray (EDS) analysis showed that compositional variations were smaller than expected, in spite of the long annealing time.
    Thermogravimetrical analysis has been used to study the kinetics of thermal deamination of bis(ethylenediamine)nickel(II)-containing aluminophosphate (Ni–CHA) which is a precursor of nickel(II)-containing chabazite-like AlPO4-34. The deamination occurs as a single–step kinetic process which is best described by the contracting cylinder model. The obtained activation energy of 200kJ/mol is mainly a reflection of the strong Ni–N coordination bond. The thermal decomposition of Ni–CHA results in the deposition of crystalline NiO particles homogeneously dispersed in the AlPO4-34 lattice. Average particle size was found to be about 5nm. The study confirms that the thermal decomposition of amine complexes of Ni(II) encapsulated inside the microporous aluminophosphate host can be a suitable method for obtaining fine nano-oxide particles.
    BaO-rich phases with the nominal compositions Ba6NbxW3−xO15−x/2 (x=1, 2), 9L-Ba9Nb2W4O26, 12-layered (12L)-Ba4Nb2WO12, and 27L-Ba9Nb6WO27 were synthesized as polycrystalline powders using solid-state techniques and characterized by X-ray powder diffractometry and transmission electron microscopy. Of these powders only the 5L2-Ba6NbxW3−xO15−x/2 (x=2) and 9L-Ba9Nb2W4O26 were obtained as single-phase materials. The formation of Ba6NbxW3−xO15−x/2 (x=1, 2) started with the occurrence of binary compounds. Thus, 5L1-Ba6NbxW3−xO15−x/2 (x=1) appeared over binary Ba4Nb2O9 in contrast to 5L2-Ba6NbxW3−xO15−x/2 (x=2), which formed through a reaction between Ba5Nb4O15 and other barium–tungsten oxides. 5L2-Ba6NbxW3−xO15−x/2 (x=2) appeared in two different polymorphs structurally related to the hexagonal Ba6Ta2WO14 and the orthorhombic β-Ba4Nb2O9. The structural refinement of the high-temperature 5L2-Ba6NbxW3−xO15−x/2 (x=2) was carried out using the space group P3m1. The fitted parameters of the hexagonal unit cell corresponded to aH=6.030(1) Å and cH=12.44(1) Å. Additional reflections of variable intensity and strong, diffuse scattering in the electron diffraction patterns indicated a strong structural disorder. The formation of 9L-Ba9Nb2W4O26, 12L-Ba4Nb2WO12, and 27L-Ba9Nb6WO27 started with the reaction between the binary compounds and continued over a series of intermediate hexagonal perovskite-type phases lying on the Ba3W2O9–Ba5Nb4O15 tie line.
    Schöne Hyalophan-Stufen aus Busovaca finden sich in den meisten der bedeutenden Mineraliensammlungen der Welt. Der aktuelle Neufund von Zagradski potok oberhalb Busovaca (Zentral-Bosnien) ist vergleichbar mit den besten Hyalophan-Funden Anfang der l950er Jahre, als die Lokalität bei Prospektionsarbeiten auf optische Quarz-Kristalle entdeckt wurde.
    Mechanochemical synthesis of lead selenide PbSe nanocrystals was performed by high-energy milling of lead and selenium powders in a planetary ball mill. The structure properties of synthesized lead selenide were characterized by XRD analysis that confirmed crystalline nature of PbSe nanocrystals. Calculated average size of PbSe crystallites was 37 nm. The methods of particle size distribution analysis, specific surface area measurement, SEM and TEM were used for the characterization of surface and morphology of PbSe nanocrystals. SEM analysis revealed agglomerates of PbSe particles. However, HRTEM analysis confirmed perfect stoichiometric PbSe cubes with NaCl structure as well. UV-VIS-NIR spectrophotometry was used to confirm the blue shift of the small particles occurring in the powder product obtained by the mechanochemical synthesis.
    A polyelectrolyte multilayer (PEM) fabricated by the layer-by-layer (LbL) self-assembly of weak polyions of polyacrylic acid (PAA) and polyallylamine (PAH) was applied as a matrix for the in situ nucleation and growth of pure and Mn-doped ZnS nanocrystallites. The nucleation and growth is initiated by the adsorption and binding of the metal ions to the ionized carboxylic groups of the weak polyions within the matrix, followed by the subsequent precipitation of semiconductor nanocrystallites with Na(2)S. Transmission electron microscopy (TEM), atomic force microscopy (AFM) and UV-vis spectroscopy were employed to establish the growth characteristics of the spherical ZnS nanocrystallites in the polyion matrix. The conformational arrangement of polyion chains induced by variation in the assembly pH is the key parameter that affects the structural and morphological characteristics of ZnS nanocrystallites. Repeating the reaction cycle resulted in an increase in the volume density of ZnS nanoparticles and further growth of the initially formed particles by the Ostwald ripening mechanism. The surface passivation of the ZnS nanocrystallites within the polyion matrix enables the enhanced radiative emission of ZnS composite films in the UV range, whereas by doping the ZnS, nanocrystallites show emission characteristic of the manganese ions in the visible region.
    Polymorphic phase transitions in Ba4Nb2O9 were studied by thermal analyses, high-temperature transmission electron microscopy and X-ray powder diffractometry. Two stable polymorphs were isolated, low-temperature -modification and high-temperature -modification, with the endothermic phase transition at 1176°C. The → transformation is accompanied by the formation of a 120° domain structure, which is a consequence of hexagonal→orthorhombic unit cell reconstruction. Reheating the presintered -Ba4Nb2O9 results in the formation of a metastable ′-modification (formerly known as β-polymorph) in the temperature range between 360° and 585°C, before the → transformation at 800°C. Above ∼490°C Ba4Nb2O9 becomes moderately sensitive to a loss of BaO. In air the surface of Ba4Nb2O9 grains decomposes to nanocrystalline Ba5Nb4O15 and BaO, which instantly reacts with atmospheric CO2 to form BaCO3. Surface reaction delays → transformation up to 866°C in air. In vacuum the loss of BaO is even more enhanced and consequently the formation of minor Ba3Nb2O8 phase is observed above 1150°C.
    Iron oxide and sulfide nanoparticles are ubiquitous in soils and sediments and play important roles in a number of environmental processes. Some iron minerals, including ferrihydrite and mackinawite, almost exclusively form as nanominerals. Their structures and chemical compositions may vary and are difficult to study. We used analytical transmission electron microscopy (TEM), including electron energy-loss spectroscopy (EELS), electron diffraction and electron crystallography for the structural characterization of synthetic iron oxide and sulfide nanocrystals.
    In the present work we propose a simple, one-step hydrothermal process for the direct crystallisation of an anatase layer, up to 2 μm thick, and with high bonding strength, on a Ti6Al4V alloy without any surface pretreatment. The samples were processed at different pH values with or without the addition of TiO2 or Ti(OH)4 , resulting in different morphologies of anatase crystals and different thicknesses of the oxide layer. The thickest, uniform, well-bonded nanocrystalline anatase layer was obtained with a hydrothermal treatment in a TiO2 suspension, whereas treating the samples in an aqueous solution led to the formation of a thin layer of {001}-oriented anatase crystallites. The layers were characterised using the SEM, TEM, XRD and XPS techniques to study their crystallinity and composition. Aluminium was absent from all the layers, while a low, equilibrium amount of vanadium remained incorporated in the anatase structure after the hydrothermal treatment with the addition of Ti4+ ions.
    Perovskite-based ceramics within the BaO–(Nb, Ta)2O5 system possess excellent microwave dielectric properties, which make them suitable for applications in communication systems. The polymorphic phase transitions and the stability of the individual polymorphs of tetra-barium di-niobate (V) (Ba4Nb2O9) were studied at different temperatures Ba4Nb2O9 ceramics were prepared via a conventional solid-state reaction route. Three Ba4Nb2O9 polymorphs were isolated. These include a hexagonal (α) and two orthorhombic (γ, β) modifications. Transmission electron microscopy (TEM) revealed an intergranular BaO-rich amorphous phase and nano-crystalline Ba5Nb4O15 in all the polymorphs, most abundantly in the α-modification. Superstructure ordering in the α-modification was confirmed by electron diffraction methods. The α-Ba4Nb2O9 was observed to be stable in the temperature range 560–1160°C; below 560°C the stable polymorph is β-Ba4Nb2O9, while above 1160°C the only stable polymorph is γ-Ba4Nb2O9.
    Scanning electron microscopy (SEM) with cathodoluminescence (CL) detection can draw a map of electronic states and chemical bonding in the specimen. The energy of CL photons gives information of Band Gap of semiconductors or Highest Occupied Molecular Orbital (HOMO)-Lowest Unoccupied MO (LUMO) of organic materials. Our new spectrometric full-color CL microscope [1] obtains CL spectra of each observing point and draws full-color CL micrograph and SEM image of 512 x 512 pixels in 8 s. The block diagram of the system is shown in Fig. 1.
    In polycrystalline materials - both metals and ceramics - understanding and controlling the microstructure is very important since vital physical properties, critical for applications, are strongly influenced by the average grain size, the grain size distribution and the porosity. The influence of the microstructure is very straightforward in the case of the exceptional current-voltage nonlinearity of ZnO-based varistor ceramics, which is closely related to the ZnO grain size: a coarse-grained microstructure results in a low breakdown voltage for the ceramics, while a fine-grained microstructure is required for a high breakdown voltage. The grain size in high-voltage varistor ceramics is controlled by the addition of a spinel-forming additive, typically Sb2O3. The grain-growth inhibition is due to the reduced grain-boundary mobility caused largely by the pinning effect of the spinel particles and defines the approach to the preparation of ZnO-based varistor ceramics, and hence also the composition. Spinel-forming dopants such as Sb2O3, TiO2 and SnO2 also result in the formation of inversion boundaries (IBs) in the ZnO grains. We have identified an IB-induced grain-growth mechanism and showed that it controls microstructure development, while the role of the spinel is subordinated. Fundamental research that revealed the true nature of the grain growth in varistor ceramics enabled us to take an entirely new approach to tailoring either a coarse- or fine-grained microstructure for ZnO-based ceramics, and will significantly alter the preparation of varistors for all voltage ranges.
    Our study focused on the formation of Ti40Zr40Ni20 and Ti45Zr35Ni17Cu3 icosahedral (i-phase) quasicrystals directly from the melt and their subsequent characterization and high-pressure hydrogenation. The samples were produced in an inert-gas melt-spinning device from a series of arc-melted precursors. By varying the wheel speeds we were able to produce a range of crystallographic structures, from amorphous, through quasicrystalline, to crystalline. The ribbon thickness showed the expected reduction with wheel speed, from 120 um to 30 um, while the Ms exhibited a surprisingly modest change with wheel speed. The XRD analysis showed that depending on the cooling rate it was possible to freeze the icosahedral phase directly from the melt, without any subsequent heat-treatment. Using the same procedure to test the range of formation wheel speeds for a comparable system we also produced samples containing up to 3 at% copper. Using transmission electron microscopy we have confirmed that the ribbons contain nanosized particles of Ti40Zr40Ni20 icosahedral phase imbedded in an amorphous matrix with the same composition. The average particle size of the i-phase was approximately 20 nm. The 5-fold symmetry was confirmed by selected-area electron diffraction and high-resolution TEM having the crystallite oriented close to the symmetry axis. Both our X-ray diffraction measurements and the TEM observations have provided direct evidence for the quasicrystalline ordering of Ti40Zr40Ni20 by rapid quenching from the melt. To test the hydrogen-absorption properties of the icosahedral phase we crushed ribbons into finer particles to provide fresh, new surfaces to aid hydrogen dissociation at the metal surface. The uptake of hydrogen was found to be critically dependent on the surface state of the Ni–Ti–Zr ribbons; even modest exposure to the atmosphere produced a protective layer of oxide on the surface that practically prevented any hydrogen being taken up by the icosahedral phase. The concentration of hydrogen in the i-phase was determined from the shift in the XRD peaks. The calculated expansion of aq was 6% and the corresponding [H]/[M] value was 1.5.
    Im Dorf Dobrova bei Dravograd (ehemals Unterdrauburg) liegt die weltbekannte klassische Fundstelle des Dravits,einem Mineral aus der Turmalin-Gruppe. Braune Dravit-Kristalle im hellgrünen Glimmerschiefer kennt man von diesem Fundort seit fast 200 Jahren. Der Dravit ist auch das erste Mineral, das seinen Namen einer heute in Slowenien liegenden Fundstelle verdankt; heute ist Dravit von vielen Vorkommen weltweit bekannt.
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