Published by MDPI

Online ISSN: 2073-4352


Figure 1. Crystal structure oC16-Cmca of Si-VI. (a) A perspective view. The atomic positions 8f and 8d are denoted as red and yellow, respectively. (b) A projection along the a-axis for nets at x=0.5 (red) and x = 0.218 and 0.282 (yellow). The structure can be viewed as an alternating sequence of planar layers formed by square-triangle nets and puckered nearly square layers. The shortest interatomic distances are marked by dark lines (modified from [4]).
Figure 2. Simulated diffraction patterns (left) and constructed Brillouin-Jones zones (right) (a) for Si- oC 16 and (b) for Cs- oC 16 with the data from Table 2. Indices hkl for reflections selected for BZ constructions are indicated on the patterns. The position of 2k F is shown by dotted (red) line. See discussion in the text. 
Electronic Origin of the Orthorhombic Cmca Structure in Compressed Elements and Binary Alloys
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May 2013


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Formation of the complex structure with 16 atoms in the orthorhombic cell, space group Cmca (Pearson symbol oC16) was experimentally found under high pressure in the alkali elements (K, Rb, Cs) and polyvalent elements of groups IV (Si, Ge) and V (Bi). Intermetallic phases with this structure form under pressure in binary Bi-based alloys (Bi-Sn, Bi-In, Bi-Pb). Stability of the Cmca - oC16 structure is analyzed within the nearly free-electron model in the frame of Fermi sphere - Brillouin zone interaction. A Brillouin-Jones zone formed by a group of strong diffraction reflections close to the Fermi sphere is the reason for reduction of crystal energy and stabilization of the structure. This zone corresponds well to the 4 valence electrons in Si and Ge and leads to assume a spd-hybridization for Bi. To explain the stabilization of this structure within the same model in alkali metals, that are monovalent at ambient conditions, a possibility of an overlap of the core and valence band electrons at strong compression is considered. The assumption of the increase in the number of valence electrons helps to understand sequences of complex structures in compressed alkali elements and unusual changes in their physical properties such as electrical resistance and superconductivity.

Figure 2. Mechanism of D band intensity enhancement at armchair edge. (a) A photo-excited electron near the K point; (b) The electron-phonon interaction of an zone-boundary A 1g mode results in the dominance of intervalley backward scattering; (c) The BZ folding leads to the appearance of two special electronic states (with the bonding [red] and antibonding [blue] orbitals): an A 1g mode can be excited from them through a first-order Raman process. In real space, this is represented by the fact that the color of the points does not change while emitting an A 1g mode.
Figure 5. Polar plot for the D band intensity. The parameters for the solid curve are a = 1, b = 1/3, and c = 0, while those for the dashed curve are a = 1 and b = c = 0.
Figure 6. A 3d plot of ReΠ µ (q, ω D ). The variables v F q and µ are given in eV. Note that ReΠ µ (q, ω) does not include the q dependence of the bare frequency.
Figure 7. The phonon dispersion relation near the Dirac point, where two principal wave vectors of the phonons (q 0 and q π ) contribute to the D band. The energy difference between ω D (q 0 ) and ω D (q π ) appears as two peaks in the D band.
The Origin of Raman D Band: Bonding and Antibonding Orbitals in Graphene

November 2012


753 Reads

In Raman spectroscopy of graphite and graphene, the $D$ band at $\sim 1355$cm$^{-1}$ is used as the indication of the dirtiness of a sample. However, our analysis suggests that the physics behind the $D$ band is closely related to a very clear idea for describing a molecule, namely bonding and antibonding orbitals in graphene. In this paper, we review our recent work on the mechanism for activating the $D$ band at a graphene edge.

Figure 1. Schematic illustration of two substitutional magnetic impurities (red circles) embedded in a graphene lattice. Also shown are the high symmetry armchair (A) and zigzag (Z) directions, and the two-atom unit cell and lattice vectors a 1 and a 2. Atoms from the two triangular sublattices are represented by filled and hollow symbols.
Figure 5. The magnetic coupling between two magnetic sites on the same sublattice as a function of their separation, D, along the armchair direction for three different impurity parameterisations: (a) (m = 0.6, δ = 0.0, t ′ = t); (b) (m = 0.6, δ = 5.0t, t ′ = 0.8t) and (c) (m = 0.6, δ = 8.0t, t ′ = 0.6t). The insets show log-log plots where a sign change in the coupling is evident from a dip feature.
Indirect Exchange and Ruderman-Kittel-Kasuya-Yosida (RKKY) Interactions in Magnetically-Doped Graphene

January 2013


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Magnetically-doped graphene systems are potential candidates for application in future spintronic devices. A key step is to understand the pairwise interactions between magnetic impurities embedded in graphene that are mediated by the graphene conduction electrons. A large number of studies have been undertaken to investigate the indirect exchange, or RKKY, interactions in graphene. Many of these studies report a decay rate faster than expected for a 2-dimensional material and the absence of the usual distance dependent oscillations. In this review we summarize the techniques used to calculate the interaction and present the key results obtained to date. The effects of more detailed parameterisations of the magnetic impurities and graphene host are considered, as are results obtained from ab initio calculations. Since the fast decay of the interaction presents an obstacle to spintronic applications, we focus in particular on the possibility of augmenting the interaction range by a number of methods including doping, spin precession and the application of strain.

Metals on Graphene: Interactions, Growth Morphology, and Thermal Stability

March 2013


366 Reads


Cai-Zhuang Wang





The nucleation and growth of Fe on graphene is highly unusual. Constantly increasing in island density with coverage is observed by experiment which indicates the presence of strong adatom predominantly repulsive interactions. We study Fe adatoms interactions on graphene by first-principles calculations and showed that the interactions between Fe adatoms consist of a short-range attraction and long-range repulsions. By investigating the adsorption energies and diffusion barriers for Fe adatoms on graphene, we also predict that Fe on graphene exhibit a three-dimensional growth mode. Fe nanostructures on graphene are also shown be stable against aggregation. The predictions from first-principles calculations are consistent with experimental observations.

Skull Melting Growth and Characterization of (ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 Crystals

January 2020


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(ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 crystals have been grown by directional melt crystallization in a cold crucible. The chemical and phase compositions of the crystals have been characterized using energy dispersion X-ray spectroscopy (EDX), Raman scattering spectroscopy and transmission electron microscopy (TEM). The X-ray photoelectron emission method has been used for determining the valence state of the Ce ions. We show that directional melt crystallization produces an inhomogeneous ceria distribution along the crystal length. The as-grown crystals are mixtures of cubic and rhombohedral zirconia modifications. The rhombohedral phase has an inhomogeneous distribution along crystal length. Melt crystallization does not produce single-phase cubic (ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 crystals. The formation of the phase structure in the crystals for different synthesis methods has been discussed.

Figure 1. Polarized light microstructure images of as-grown crystals: (a) 9ScSZ, (b) 9Sc0.5YbSZ, and (c) 9Sc1YbSZ.
Figure 2. Raman spectra of as-grown and as-annealed (a) 9ScSZ, (b) 9Sc0.5YbSZ, and (c) 9Sc1YbSZ crystals.
Figure 3. (a) Conductivity of test crystals vs temperature in Arrhenius coordinates and (b) Conductivity of test crystals vs. Yb 2 O 3 concentration.
Figure 4. Conductivity of as-grown and as-annealed (a) 9ScSZ, (b) 9Sc0.5YbSZ, and (c) 9Sc1YbSZ crystals as a function of temperature.
Figure 5. 1173 K conductivity of crystals as-grown and as-annealed at 1000 C for 400 h.
Phase Stability and Transport Properties of (ZrO2)0.91−x(Sc2O3)0.09(Yb2O3)x Crystals (x = 0–0.01)

January 2021


131 Reads

Phase stability and transport properties of (ZrO2)0.91−x(Sc2O3)0.09(Yb2O3)x crystals (x = 0–0.01) have been studied before and after air annealing at 1000 °C for 400 h. The crystals have been grown by radio frequency (RF) heating in a cold crucible. The microstructure, phase composition, and electrical conductivity of the crystals have been studied using optical microscopy, X-ray diffraction, Raman spectroscopy, and impedance spectroscopy. Phase stability and degradation of ionic conductivity of the crystals upon long-term high-temperature heat treatment have been discussed. We show that the stabilization of ZrO2 co-doped with 9 mol.% Sc2O3 and 1 mol.% Yb2O3 provides transparent uniform crystals with the pseudocubic t″ phase structure having high phase stability. Crystals of this composition had the highest conductivity in the entire temperature range. Long-term high-temperature annealing of these crystals did not lead to conductivity degradation.

Figure 6. (a) Temperature-dependent P-E loops, (b) temperature-dependent ferroelectric polarization, (c) P-E loops for 100 k cycles, and (d) ferroelectric polarization of the (Ba 0.6 Sr 0.3 Ca 0.1 )TiO 3 ·0.03(Bi 2 O 3 ·3TiO 2 ) ceramics after 100 k cycles.
High-Permittivity and Bias-Voltage-Insensitive (Ba,Sr,Ca)TiO3·0.03(Bi2O3·3TiO2) Ceramics with Y5U Specification
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November 2023


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Class II ceramics are a material with high permittivity but low reliability of their capacitance and bias voltage due to high the temperature sensitivity of their dielectric permittivity. In this work, a BST-based (Ba0.9−xSrxCa0.1)TiO3·0.03(Bi2O3·3TiO2) (x = 0.2, 0.25, 0.3, 0.35, 0.4) composition with Y5U characteristics was investigated through compositional control to develop high-permittivity and voltage-stable ceramic compositions. Sr doping can increase the breakdown strength (Eb) but decreases the Curie temperature (Tc). The composition at x = 0.3 can obtain optimal comprehensive electrical properties, with high permittivity of 4206, low dielectric loss of ~0.009, and moderate breakdown strength (Eb) of 77.6 kV/cm, which meets Y5U specifications. Typically, a low bias-voltage dependence of capacitance is confirmed with a variation rate of 7.64% under 20 kV/cm. This strategy provides a promising candidate for high-permittivity Class II ceramic dielectrics that can be used in this field.

Figure 3. X-ray diffraction patterns of samples with the amount of antimony: (a) Wide Range, (b) Narrow Range.
Electrical properties of samples with the amount of antimony.
Crystal Structure and Electrical Characteristics of (0.965)(Li0.03(Na0.5K0.5)0.97)(Nb1−xSbx)O3−0.035(Bi0.5Na0.5)0.9(Sr)0.1ZrO3 Ceramics Doped with CuO, B2O3, and ZnO

July 2021


62 Reads

Recently, the need has arisen to enhance the piezoelectric properties and temperature stability of (Na,K)NbO3 system ceramics. The (0.965)(Li0.03(Na0.5K0.5)0.97)(Nb1−xSbx)O3−0.035 (Bi0.5Na0.5)0.9(Sr)0.1ZrO3 ceramics were newly manufactured using the sintering aids of CuO, B2O3, and ZnO as a function of antimony substitution, and the their crystal structure and electrical characteristics were analyzed. The grain size was apparently refined as the amount of antimony increased. The dielectric constant was enhanced and Curie temperature was decreased due to the content of the antimony substitution. The x = 0.07 sample sintered at 1060 °C presented the best electrical characteristics, which were bulk density = 4.488 g/cm3, piezoelectric constant d33 = 330 pC/N, electromechanical coupling factor kp = 0.427, mechanical coupling factor Qm = 61, and dielectric constant εr = 2521. We believe that the x = 0.07 sample is the best material for piezoelectric speakers.

Actual composition, lattice parameter, T c , Hc 2 and carrier density of In x Sn 1−x Te crystals, note that the actual composition was normalized to Te content.
Actual composition, lattice parameter, Tc, Hc2 and carrier density of InxSn1−xTe crystals, note that the actual com- position was normalized to Te content.
Synthesis of Superconducting InxSn1−xTe (0.04 < x < 0.1) Large Single Crystal by Liquid Transport Method

April 2021


8 Reads

In this work, a new crystal growth technique called the liquid transport method was introduced to synthesize single crystals of a topological superconductor candidate, InxSn1−xTe (IST). Crystals with the size of several millimeters were successfully synthesized, and were characterized by X-ray diffraction, scanning electron microscopy with energy-dispersive spectroscopy as well as electronic transport measurements. Lattice parameters decreased monotonously with the increase of indium content while hole density varied in reverse. Superconductivity with the critical temperature (Tc) around 1.6 K were observed, and the hole densities were estimated to be in the order of 1020 cm−3. The upper critical fields (Bc2) were estimated to be 0.68 T and 0.71 T for In0.04Sn0.96Te and In0.06Sn0.94Te, respectively. The results indicated that the quality of our crystals is comparable to that grown by the chemical vapor transport method, but with a relatively larger size. Our work provides a new method to grow large single crystals of IST and could help to solve the remaining open questions in a system that needs large crystals, such as a superconducting pairing mechanism, unconventional superconductivity, and so on.

Figure 9. The {001} pole figures after high-temperature annealing with different decarbonization annealing times of (a) 3 min, (b) 5 min and (c) 7 min.
Content of main texture of decarbonized annealing samples (%).
Texture content after 850 • C high-temperature annealing with different decarbonization annealing times.
Magnetic properties after high-temperature annealing with different decarbonization annealing times.
Effect of Holding Time of Decarbonization Annealing on Recrystallization in Fe-3.2%Si-0.047Nb% Low-Temperature Oriented Silicon Steel

October 2021


57 Reads

In this study, the effects of decarburization annealing time on the primary recrystallization microstructure, the texture and the magnetic properties of the final product of 0.047% Nb low-temperature grain-oriented silicon steel were investigated by means of OM, EBSD and XRD. The results show that when the decarburization annealing condition is 850 °C for 5 min, the uniform fine primary recrystallization microstructure can be obtained, and the content of favorable texture {111} <112> is the highest while that of unfavorable texture {110} <112> is the lowest, which is mostly distributed near the central layer. At the same time, there are the most high-energy grain boundaries with high mobility in the primary recrystallization microstructure of the sample annealed at 850 °C for 5 min, and the ∑9 boundary has the highest percentage of grain boundaries. The samples with different decarburization annealing time were annealed at high temperature. It was found that perfect secondary recrystallization occurred after high-temperature annealing when the decarburization annealing condition was 850 °C for 5 min. The texture component was characterized by a single Goss texture, and the size of the Goss grain reached 4.6 mm. Under such annealing conditions, the sample obtained shows the optimal soft magnetic properties of B800 = 1.89 T and P1.7/50 = 1.33 w/kg.

Crystal Structure of Bismuth-Containing Samarium Iron–Aluminium Borates Sm1−xBixFe3−yAly(BO3)4 (x = 0.05–0.07, y = 0–0.28) in the Temperature Range of 25–500 K

July 2023


61 Reads

Structural features of new mixed bismuth-containing samarium iron–aluminium borate single crystals Sm1−xBixFe3−yAly(BO3)4 (x = 0.05–0.07, y = 0–0.28) were studied using X-ray diffraction analysis based on aluminium content and temperature in the range 25–500 K. The crystals were grown using the solution-in-melt technique with Bi2Mo3O12 in a flux. The composition of the single crystals was analyzed using energy-dispersive X-ray fluorescence and energy-dispersive X-ray elemental analysis. Temperature dependencies of Sm1−xBixFe3−yAly(BO3)4 unit-cell parameters were studied. Negative thermal expansion was identified below 100 K and represented by characteristic surfaces of the thermal expansion tensor. (Sm,Bi)–O, (Sm,Bi)–(Fe,Al), (Fe,Al)–(Fe,Al), and (Fe,Al)–O interatomic distances decreased with the addition of aluminium atoms. An increase in the (Fe,Al)–(Fe,Al) intrachain bond length at low temperatures in the magnetically ordered state weakened this bond, whereas a decrease in the (Fe,Al)–(Fe,Al) interchain distance strengthened super-exchange paths between different chains. It was found that the addition of aluminium atoms influenced interatomic distances in Sm1−xBixFe3−yAly(BO3)4 much more than lowering the temperature from 293 K to 25 K. The effect of aluminium doping on magnetoelectric properties and structural symmetry of rare-earth iron borates is also discussed.

Figure 1. (a) Evolution of the neutron diffraction patterns of 0.06LiNbO 3 -0.94K 0.5 Na 0.5 NbO 3 (KNNL6) as a function of temperature from 290 to 773 K. hkl reflections are indexed based on a cubic perovskite structure. Inset is a perovskite structure of KNNL6. The arrows mark changes in hkl peak profiles, which indicate phase transitions. (b) Neutron diffraction patterns of {400} reflections as a function of temperature. The x-axis refers to the wavevector Q.
Figure 6. Atomic displacement and octahedral distortion as a function of temperature: (a) Nb fractional displacement along 100 S 100 and [001] (S 001 ) directions, and (b) net Nb fractional displacement as a function of temperature from 290 to 773 K. (c) Octahedral distortion parameter as a function of temperature from 290 and 773 K for the local and average structures. Note that open blue symbols represent parameters obtained from average Rietveld refinement, while the closed pink symbols represent parameters obtained from PDF refinement in the r range of 1.7-10 Å. (d,e) Illustration of the NbO6 octahedron in the average structure at 290 (left top) and 773 K (right top), respectively. (f,g) Illustration of the NbO6 octahedron in the local structure at 290 (left bottom) and 773 K (right bottom), respectively. The indicated Nb-O bond lengths in (d-g) are in the Angstroms (Å).
Structural parameters, fractional atomic coordinates, and equivalent isotropic displacement parameters (U iso in Å 2 ) from the Rietveld refinement and PDF fit (1.7-10 Å) results of neutron data of KNNL6 at various temperatures. Rietveld and PDF Refinement of KNNL6 at 773K
A Structural Study of 0.06LiNbO3-0.94K0.5Na0.5NbO3 from Neutron Total Scattering Analysis

April 2021


104 Reads

The structure of ferroelectric 0.06LiNbO3-0.94K0.5Na0.5NbO3 (KNNL6) was investigated by the neutron total scattering method in the temperature range of 290–773 K. The Rietveld analysis using the powder neutron diffraction data in the range of 290–773 K indicates transition from a two-phase (monoclinic and tetragonal) mixture at room temperature to tetragonal and cubic phases at higher temperatures. However, characterization of the local structure by the pair distribution function (PDF) method indicates that the local structure (r ≲ 10 Å) stays monoclinic over the same temperature range. Besides, the local oxygen octahedral distortion exhibits smaller changes with temperature than what is observed for the long-range average structure.

Figure 1. Measured (a) and calculated (c) powder diffraction patterns of Cs8Tl11Cl0.8; Measured (b) and calculated (d) powder diffraction patterns of Cs8Tl11Br0.9 (diffractograms generated by the program STOE WinXPOW adapted from [22], with permission from ? 1887 STOE.
Figure 6. The unit cell of Cs8Tl11Br0.9 shows the two characteristic components: Tl11 clusters and the distorted cubic arrangement around the halide atom.
Structural chemistry of halide including thallides A8 Tl11 X1−n (A = K, Rb, Cs; X = Cl, Br; n = 0.1–0.9)

August 2018


99 Reads

A8Tl11 (A = alkali metal) compounds have been known since the investigations of Corbett et al. in 1995 and are still a matter of current discussions as the compound includes one extra electron referred to the charge of the Tl117− cluster. Attempts to substitute this additional electron by incorporation of a halide atom succeeded in the preparation of single crystals for the lightest triel homologue of the group, Cs8Ga11Cl, and powder diffraction experiments for the heavier homologues also suggested the formation of analogous compounds. However, X-Ray single crystal studies on A8Tl11X to prove this substitution and to provide a deeper insight into the influence on the thallide substructure have not yet been performed, probably due to severe absorption combined with air and moisture sensitivity for this class of compounds. Here, we present single crystal X-Ray structure analyses of the new compounds Cs8Tl11Cl0.8, Cs8Tl11Br0.9, Cs5Rb3Tl11Cl0.5, Cs5.7K2.3Tl11Cl0.6 and K4Rb4Tl11Cl0.1. It is shown that a (partial) incorporation of halide can also be indirectly determined by examination of the Tl-Tl distances, thereby the newly introduced cdd/cdav ratio allows to evaluate the degree of distortion of Tl117− clusters.

Structural parameters of BST x (x = 0.1, 0.3 and 0.7) obtained from Rietveld analysis of XRD patterns.
The remanent polarization Pr and coercive field Ec of BSTx (x = 0.1, 0.3 and 0.7) ferroelectric capacitors.
High energy storage density and energy storage efficiency of BST x -based capacitors.
Phase Transition and Energy Storage Density in Lead-Free Ferroelectric Ba1−xSrxTiO3 (x = 0.1, 0.3, and 0.7) Capacitors

April 2023


35 Reads

Structure, phonon, and energy storage density in Sr2+-substituted lead-free ferroelectric Ba1−xSrxTiO3 (BSTx) for compositions x = 0.1, 0.3, and 0.7 were investigated using X-ray diffraction, Raman, and ferroelectric polarization measurements as a function of temperature. The samples were tetragonal for x = 0.1 with a large c/a ratio. The tetragonal anisotropy was decreased upon increasing x and transforming to cubic for x = 0.7. The changes in structural and ferroelectric properties were found to be related to the c/a ratios. The temperature-dependent phonon spectroscopy results indicated a decrease in tetragonal–cubic phase transition temperature, Tc, upon increasing x due to a reduction in the lattice anisotropy. The intensity of ~303 cm−1 E(TO2) mode decreased gradually with temperature and finally disappeared around the tetragonal ferroelectric to cubic paraelectric phase at about 100 ℃ and 40 ℃ for x = 0.1 and 0.3, respectively. A gradual reduction in the band gap Eg of BSTx with x was evident from the analysis of UV-visible absorption spectra. The energy storage density (Udis) of the ferroelectric capacitors for x = 0.7 was ~0.20 J/cm3 with an energy storage efficiency of ~88% at an applied electric field of 104.6 kV/cm. Nearly room temperature transition temperatures TC and reasonably fair energy storage density of the BSTx capacitors were found.

Studies of Optical, Dielectric, Ferroelectric, and Structural Phase Transitions in 0.9[KNbO3]-0.1 [BaNi1/2Nb1/2O3−δ]

December 2021


84 Reads

The compound 0.9[KNbO3]-0.1[(BaNi1/2Nb1/2O3−δ] (KBNNO), a robust eco-friendly (lead-free) ferroelectric perovskite, has diverse applications in electronic and photonic devices. In this work, we report the dielectric, ferroelectric, and structural phase transitions behavior in the KBNNO compound using dielectric, X-ray diffraction, and Raman studies at ambient and as a function of temperature. Analyses of X-ray diffraction (XRD) data at room temperature (rtp) revealed the orthorhombic phase (sp. Gr. Amm2) of the compound with a minor secondary NiO cubic phase (sp. Gr. Fm3m). A direct optical band gap Eg of 1.66 eV was estimated at rtp from the UV–Vis reflectance spectrum analysis. Observation of non-saturated electric polarization loops were attributed to leakage current effects pertaining to oxygen vacancies in the compound. Magnetization studies showed ferromagnetism at room temperature (300 K) in this material. XRD studies on KBNNO at elevated temperatures revealed orthorhombic-to-tetragonal and tetragonal-to-cubic phase transitions at 523 and 713 K, respectively. Temperature-dependent dielectric response, being leaky, did not reveal any phase transition. Electrical conductivity data as a function of temperature obeyed Jonscher power law and satisfied the correlated barrier-hopping model, indicating dominance of the hopping conduction mechanism. Temperature-dependent Raman spectroscopic studies over a wide range of temperature (82–673 K) inferred the rhombohedral-to-orthorhombic and orthorhombic-to-tetragonal phase transitions at ~260, and 533 K, respectively. Several Raman bands were found to disappear, while a few Raman modes such as at 225, 270, 289, and 831 cm−1 exhibited discontinuity across the phase transitions at ~260 and 533 K.

Main acquisition and structure refinement parameters for Me β-Ca 3 (PO 4 ) 2 tricalcium phosphate (β-TCP) (FMLQ = full matrix least squares; Pearson VII [34]).
Semi-quantitative EDS analyses for Ca 2.90 Me 0.10 (PO 4 ) 2 (Me = Mn, Ni, Cu) samples expressed in wt % (CaO, MeO, P 2 O 5 ) and atoms per formula unit (Ca, Me, P). Crystal formula is based on five cations.
Refined fractional atomic coordinates, Wyckoff site, isotropic displacement atomic parameters, and occupancy factors for Ca 2.9 Ni 0.1 (PO 4 ) 2 .
New Ca2.90(Me2+)0.10(PO4)2 β-tricalcium Phosphates with Me2+ = Mn, Ni, Cu: Synthesis, Crystal-Chemistry, and Luminescence Properties

June 2019


228 Reads

C a 2.90 M e 0.10 2 + ( P O 4 ) 2 (with Me = Mn, Ni, Cu) β-tricalcium phosphate (TCP) powders were synthesized by solid-state reaction at T = 1200 °C and investigated by means of a combination of scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, and luminescence spectroscopy. SEM morphological analysis showed the run products to consist of sub spherical microcrystalline aggregates, while EDS semi-quantitative analysis confirmed the nominal Ca/Me composition. The unit cell and the space group were determined by X-ray powder diffraction data showing that all the compounds crystallize in the rhombohedral R3c whitlockite-type structure, with the following unit cell constants: a = b = 10.41014(19) Å, c = 37.2984(13) Å, and cell volume V = 3500.53(15) Å3 (Mn); a = b = 10.39447(10) Å, c = 37.2901(8) Å; V = 3489.22(9) Å3 (Ni); a = b = 10.40764(8) Å, c = 37.3158(6) Å, V = 3500.48(7) Å3 (Cu). The investigation was completed with the structural refinement by the Rietveld method. The FTIR spectra are similar to those of the end-member Ca β-tricalcium phosphate (TCP), in agreement with the structure determination, and show minor band shifts of the (PO4) modes with the increasing size of the replacing Me2+ cation. Luminescence spectra and decay curves revealed significant luminescence properties for Mn and Cu phases.

Tetragonal-to-Tetragonal Phase Transition in Lead-Free (KxNa1-x)NbO3 (x=0.11 and 0.17) Crystals

June 2014


515 Reads

Lead free piezoelectric crystals of (KxNa1-x)NbO3 (x = 0.11 and 0.17) have been grown by the modified Bridgman method. The structure and chemical composition of the obtained crystals were determined by X-ray diffraction (XRD) and electron probe microanalysis (EPMA). The domain structure evolution with increasing temperature for (KxNa1-x)NbO3 (x = 0.11 and 0.17) crystals was observed using polarized light microscopy (PLM), where distinguished changes of the domain structures were found to occur at 400 degrees C and 412 degrees C respectively, corresponding to the tetragonal to tetragonal phase transition temperatures. Dielectric measurements performed on (K0.11Na0.89)NbO3 crystals exhibited tetragonal to tetragonal and tetragonal to cubic phase transitions temperatures at 405 degrees C and 496 degrees C, respectively.

Figure 6a shows the isotropic Co-L 2,3 XAS spectrum of Sr 4 Co 3 O 7.5+x Cl 2 taken at room temperature together with those of Sr 2 CoO 3 Cl [17], EuCoO 3 [17], and CoO serving as HS-Co 3+ , LS-Co 3+ , and HS-Co 2+ references. It is well known that the soft XAS at the Co-L 2,3 edges is very sensitive to the spin, orbital and valence states of the ion [14,17,21,22]. As shown in Figure 6a, the center of gravity of the L 2,3 white lines of Sr 4 Co 3 O 7.5+x Cl 2 locates at the same photon energies as observed for the Co 3+ reference samples Sr 2 CoO 3 Cl and EuCoO 3 , thus, indicating the presence of a Co 3+ valence state in Sr 4 Co 3 O 7.5+x Cl 2 . The absence of any pronounced spectral feature at 777.8 eV indicates a negligible amount of Co 2+ impurities in Sr 4 Co 3 O 7.5+x Cl 2 . Furthermore, the multiplet spectral feature of Sr 4 Co 3 O 7.5+x Cl 2 is very different from that of EuCoO 3 , implying the different electronic structures of these two compounds. On the other hand, the spectral features at both the Co-L 3 and the Co-L 2 edges of the Sr 4 Co 3 O 7.5+x Cl 2 are almost identical to those of the HS-Co 3+ reference sample Sr 2 CoO 3 Cl, which indicates the presence of a high-spin Co 3+ state in Sr 4 Co 3 O 7.5+x Cl 2 . More spectroscopic evidence for the HS nature of the Co 3+ ions in the Sr 4 Co 3 O 7.5+x Cl 2 can be found from the O-K XAS spectrum.
Crystal Growth and Physical Properties of Sr4Co3O7.5+xCl2 Single Crystals (x ∼ 0.14)

November 2019


121 Reads

We report on the single crystal growth and physical properties of the triple-layer cobalt oxychloride Sr 4 Co 3 O 7 . 5 + x Cl 2 (x∼ 0.14) with 4-3-10 Ruddlesden–Popper type structure that was synthesized by a KCl-SrCl 2 flux method. The crystal structure was determined by means of single crystal X-ray diffraction. In this quasi two dimensional (2D) material two pyramidal CoO 5 layers and a central Co oxide layer with random oxygen deficiencies are forming the layered Co oxide blocks. These blocks are separated by Cl − -ions which are interacting via Van der Waals forces, thus, enhancing the quasi 2D nature of this compound. The soft X-ray absorption spectra at the Co-L 2 , 3 edge and O-K edge indicate that Co ions are in high spin +3 state which is in agreement with the single crystal X-ray diffraction measurements that indicate basically pyramidal oxygen environments for the Co 3 + ions in this compound.

Figure 4. The typical J–V curves of the perovskite solar cells based on (FAPbI3)0.85(MAPbBr3)0.15 using different molar ratios of MACl additives. 
CH3NH3Cl Assisted Solvent Engineering for Highly Crystallized and Large Grain Size Mixed-Composition (FAPbI3)0.85(MAPbBr3)0.15 Perovskites

September 2017


683 Reads

High-quality mixed-cation lead mixed-halide (FAPbI3)0.85(MAPbBr3)0.15 perovskite films have been prepared using CH3NH3Cl additives via the solvent engineering method. The UV/Vis result shows that the addition of additives leads to enhanced absorptions. XRD and SEM characterizations suggest that compact, pinhole-free and uniform films can be obtained. This is attributable to the crystallization improvement caused by the CH3NH3Cl additives. The power conversion efficiency (PCE) of the F-doped SnO2 (FTO)/compact-TiO2/perovskite/Spiro-OMeTAD/Ag device increases from 15.3% to 16.8% with the help of CH3NH3Cl additive.

Figure 6. Relationship between the low-cycle fatigue life and strain amplitude of the TiAl alloy (a) and the life prediction results by the Manson-Coffin model (b).
Figure 8c,d show the typical fracture surfaces of the fatigue specimens at 400 °C. The dimple becomes sharper and more irregular, grain boundary separation also occurs, and the trans-granular fracture of equiaxed grains becomes more significant with increasing strain amplitude. In the lamellar colony, the trans-lamellar fracture is dominant entirely. Under a small strain amplitude, the characteristics of inter-lamellar fracture are more obvious at the edge of the dimple. Under a high strain amplitude, the inter-lamellar fracture becomes occasionally visible, and inter-lamellar separation becomes obvious. All fracture morphologies of the strain-controlled fatigue specimens indicate that the fracture mechanism of the TiAl alloy has a high dependency on the temperature. The plasticity of the material at 750 °C is more significant, while the characteristics of brittle fracture are more prominent at 400 °C, which can reasonably explain the distinction in the cyclic mechanical behavior of the TiAl alloy at different temperatures. Furthermore, the fracture morphologies of fatigue specimens also demonstrate that the fracture mechanism of the TiAl alloy could be transformed with the load amplitude despite the temperature.
EDS results of the element contents on the fracture of specimens at different tempera- tures.
High Temperature Fatigue Behavior and Failure Mechanism of Ti-45Al-4Nb-1Mo-0.15B Alloy

November 2022


37 Reads

Strain-controlled low cycle fatigue experiments were carried out on the TiAl alloy Ti-45Al-4Nb-1Mo-0.15B at 400 °C and 750 °C to reveal the cyclic mechanical behavior and failure mechanism. The TiAl alloy presents stable cyclic characteristics under fatigue loading at elevated temperatures. No obvious cyclic softening or cyclic hardening was manifested during experiments. The cyclic stress–strain relationship is well described by the Ramberg–Osgood equation. The fatigue lifetime at different temperatures has a log-linear relationship with the total strain ranges. The fracture morphology indicates the main fracture mode of fatigue specimens at 400 °C is a brittle fracture, while there is a ductile fracture at 750 °C. Meanwhile, the trans-lamellar fracture is dominant for the lamellar microstructure and the percentages of the inter-lamellar fracture decreases with the strain amplitude.

Melt treatment parameters under different conditions.
Practical chemical composition of the test alloy (wt. %).
Effects of ESMT on Microstructure and Mechanical Properties of Al-8Zn-2Mg-1.5Cu-0.15Sc-0.15Zr Cast Alloy in Squeeze Casting Process

July 2022


33 Reads

Al-8Zn-2Mg-1.5Cu-0.15Sc-0.15Zr alloy with high-strength performance as well as good castability has been developed. In this study, effects of electromagnetic stirring melt treatment (ESMT) on microstructure and mechanical properties of the alloy in the squeeze casting process were investigated. The results show that solidification structure and mechanical properties are significantly improved by ESMT; compared with the conventional squeeze casting, the average grain size decreases from 112 μm without ESMT to 53 μm with ESMT. Meanwhile coarse primary Al3(Sc, Zr) particles unavoidably occurred in cases without ESMT disappear, and segregation degree of the main elements of Zn, Mg, Cu are greatly alleviated; the tensile strength increases from 590 MPa to 610 MPa, and the elongation increases from 9% to 11%. The structure refinement and homogenization should owe to uniform temperature and composition distribution by ESMT under squeeze casting with rapid solidification.

Figure 1. Effects of ageing time on room temperature mechanical properties of Al-5Cu-0.8Mg-0.15Zr-0.2Sc(-0.5Ag) (a) tensile strength; (b) elongation at break.
Steady-state creep rates of peak-aged Al-5Cu-0.8Mg-0.15Zr-0.2Sc(-0.5Ag) under the same conditions.
Effects of Ag on High-Temperature Creep Behaviors of Peak-Aged Al-5Cu-0.8Mg-0.15Zr-0.2Sc(-0.5Ag)

July 2023


18 Reads

The tensile creep of Al-5Cu-0.8Mg-0.15Zr-0.2Sc(-0.5Ag) was tested at 150–250 °C and 125–350 MPa, and the effect of Ag on the high-temperature creep of Al-Cu-Mg alloys was discussed. After the addition of Ag, the high-temperature creep performances of the alloy were significantly improved at 150 °C/300 MPa and 200 °C/(150 MPa, 175 MPa). Then, constitutive relational models of the alloy during high-temperature creep were built, and the activation energy was calculated to be 136.65 and 104.06 KJ/mol. Based on the thermal deformation mechanism maps, the high-temperature creep mechanism of the alloy was predicted. After the addition of Ag, the creep mechanism of the alloy at 150 °C transitioned from lattice diffusion control to grain boundary diffusion control. At 250 °C, the mechanism was still controlled by grain boundary slip, but as the stress index increased and after Ag was added, the alloy fractures lead to the formation of dimples, thus improving the high-temperature creep performance.

Texture and Microstructure Evolution of Ultra-High Purity Cu-0.1Al Alloy under Different Rolling Methods

September 2021


64 Reads

The microstructure and texture distribution of ultra-high purity Cu-0.1Al alloy target play a key role in the quality of the sputtering film. The Cu-0.1Al alloy sheets were processed by unidirectional (UR) and cross rolling (CR), and X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) technologies were adopted to observe the texture and microstructure evolution. XRD results reveal that the texture types vary greatly in UR and CR due to the change of strain path. As the strain increases to 90%, S texture occupies the most, followed by copper texture in the UR sample, while brass texture dominates the most in the CR sample. Additionally, the orientation density of texture does not increase significantly with the increase of strain but shows a downward trend both in UR and CR modes. EBSD analysis demonstrates that compared with UR, the deformation microstructure in CR is more uniform, and the layer spacing between the deformation bands is smaller, which can reduce the local-region stress concentration. After the completion of recrystallization, the difference in average grain size between the UR and CR-annealed samples is not significant, and the recrystallized grains become much finer with the increase of strain, while more equiaxed grains can be observed in CR-annealed samples.

Figure 5. Microstructures of Col (a-d) and Mech (e-h) PMN-10PT samples from combined SEM (a, b, e) and TEM (c, d, fh) techniques. Circles in (a) point out the triple-junction points (TJP), magnified in (b-d), where secondary phases of Mgand Pb-silicates crystallized. Arrows in (e) point out the MgO grains at the grain boundaries and trapped MgO inclusions in the matrix grains. Panel (f) shows clear TJPs of the Mech sample. Panels (g) and (h) are TEM images of MgO inclusions.
Chemical composition and the standard deviation (STDEV) of the Col and the Mech ceramics, determined by WDXS.
Influence of Synthesis-Related Microstructural Features on the Electrocaloric Effect for 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 Ceramics

April 2021


112 Reads

Despite having a very similar electrocaloric (EC) coefficient, i.e., the EC temperature change divided by the applied electric field, the 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 (PMN-10PT) ceramic prepared by mechanochemical synthesis exhibits a much higher EC temperature change than the columbite-derived version, i.e., 2.37 °C at 107 °C and 115 kV/cm. The difference is due to the almost two-times-higher breakdown field of the former material, 115 kV/cm, as opposed to 57 kV/cm in the latter. While both ceramic materials have similarly high relative densities and grain sizes (>96%, ≈5 μm) and an almost correct perovskite stoichiometry, the mechanochemical synthesis contributes to a lower level of compositional deviation. The peak permittivity and saturated polarization are slightly higher and the domain structure is finer in the mechanochemically derived ceramic. The secondary phases that result from each synthesis are identified and related to different interactions of the individual materials with the electric field: an intergranular lead-silicate-based phase in the columbite-derived PMN-10PT and MgO inclusions in the mechanochemically derived ceramic.

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