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... The diffractograms were obtained from 10° to 100° at a step size of 0.013°, with a time analysis of 67 s at each step, in a graphite monochromator in the plane geometry for diffracted beam. PXRD patterns of the crystalline powders were refined by the Rietveld method [18] using GSAS/EXPGUI software [19,20]. ...
... After the calcination process, no spurious phases were observed for SCSO, CCSO, and BCSO. Diffractogram data were refined by the Rietveld method [18], using GSAS/EXPGUI software [19,20] and are presented in Fig. 1. As can be seen in Table 1, low values of agreement indices for all samples show that the parameters of Rietveld refinements were satisfactory, with weighted profile R-factor (R WP ) below 20% and χ 2 near unity [26]. ...
A series of MCuSi4O10 (M = Ca²⁺, Sr²⁺ and Ba²⁺) electroceramics have been prepared by solid-state reaction and sintered at 1150 (CCSO (CaCuSi4O10)), 1100 (SCSO (SrCuSi4O10)), and 1150 °C (BCSO (BaCuSi4O10)). The structure and dielectric properties of the samples were studied by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), impedance spectroscopy at radiofrequency (RF) and dielectric resonator antenna (DRA) at microwaves. The electroceramics presented values of thermo-activated process and activation energy (Ea) between 0.65 and 1.66 eV. In addition, fitting plots showed the equivalent circuit consisting of two parallel (R/CPE) connected in series, which is associated with the grain and grain boundary electrical contributions. The microwave dielectric properties showed dielectric constant (εr) of 3.47, 5.04, and 5.40 and quality factor (Q x f) of 11,350.00, 11,438.60, and 28,983.00 GHz for CCSO, SCSO, and BCSO, respectively. All the samples have a great potential for microwave applications, especially the CCSO- and BCSO-based DRA, due to the near-zero temperature coefficient of resonant frequency (τf) values (− 2.24 and − 7.41 ppm.°C⁻¹, respectively). The preliminary results indicate that MCuSi4O10 electroceramics are satisfactory for use as a commercial antenna for C- and X-band applications.
... The scanning was done at 200 °C, 400 °C, 600 °C, 800 °C and 1000 °C in the 2 range of 10 to 90° with the same scan rate above. Rietveld refinement (GSAS software [36]) was applied for the obtained XRD patterns. The coefficients of thermal expansion (CTE) were calculated from change of lattice parameters (a, b, c, and β) with increased temperatures. ...
Rare-earth disilicates are promising candidates for thermal and environmental barrier coatings (TEBC) in gas turbines that safeguard SiCf/SiC ceramic matrix composites (CMCs) from thermal degradation and environmental attacks. Here, we report a systematic investigation on novel TEBC material, γ-Y1.5Yb0.5Si2O7. The γ-phase quarter molar ytterbium–doped yttrium disilicate exhibited low thermal conductivity (1.72 W·m⁻¹·K⁻¹ at 1200 °C) and reduced intrinsic thermal expansion (3.17 ± 0.22 × 10⁻⁶ K⁻¹ up to 1000 °C), ensuring promisingly effective thermal insulation and minimized thermal stress with CMC substrates. Using density functional theory (DFT), the heat capacity of γ-Y1.5Yb0.5Si2O7 was predicted higher than that of undoped γ-Y2Si2O7. Comparing these predictions to results calculated using the Neumann–Kopp (NK) rule revealed only minor variations. A metastable CMAS interaction byproduct, cyclosilicate phase Ca3RE2(Si3O9)2, was identified based on energy dispersive X-ray spectrometer (EDS) and electron backscatter diffraction (EBSD) techniques, appearing at 1300 °C but disappearing at 1400 °C. The γ-Y1.5Yb0.5Si2O7 exhibited good CMAS resistance on both dense pellets and sprayed coatings, forming a protective apatite (Ca2RE8(SiO4)6O2) interlayer that effectively hindered CMAS infiltration at evaluated temperatures. The relatively higher Y:Yb atomic ratio (> 3) in the apatite grains indicate differential reactivity with molten CMAS and provides crucial insights into the CMAS corrosion mechanism. These findings highlight the potential of γ-Y1.5Yb0.5Si2O7 as a CMC coating material, emphasizing the need for tailored microstructural optimization as a thermal sprayed coating to enhance long-term performance in extreme gas turbine environments.
... The powder samples were back-loaded on a flat sample-holder, and PXRD patterns were collected over a 2θ angular range of 5-80 • , with 0.0167 • per step and a counting time of 90 s/step. Qualitative analyses were preliminary done employing Match! software, and then the phase amounts were evaluated from PXRD patterns by means of the full profile Rietveld Refinement Method [26], implemented in GSAS software, and with EXPGUI as graphical interface [27]. The micro-Raman measurements were carried out with the LABRAM HR800 instrument (Horiba Jobyn-Yvon) using a 50X objective (0.75 NA, laser spot size about 1 µm) and the 405 nm excitation provided by a solid-state laser produced by Integrated Optics. ...
A R T I C L E I N F O Keywords: Microwave chemistry Carbon capture utilization and storage Magnesium hydroxy-carbonate hydrates X-ray diffraction Raman spectroscopy Electron microscopy A B S T R A C T The water-mediated mineral carbonation represents a promising solution for the capture and the storage of atmospheric CO 2. Even though this reaction might be spontaneous for a number of Mg-and Ca-rich mineral phases, it is characterized by considerable activation barriers. In order to make it effective, associated energy costs related to the achievement of adequate reaction conditions must be minimized. Microwave chemistry is known to provide for substantial increments of the reaction rate for several systems. We applied here microwave chemistry to the process of carbonation of aqueous slurries of brucite, a model system of Mg-rich mineral, subjected to partial pressures of CO 2 as low as 6 bar and to no other additive. The temperature of the reactor was finely varied while the radiation power and the reactor pressure were monitored in real-time. The radiation power was used to estimate the radiation energy budget needed to complete the carbonation process, whereas the reactor pressure was used as a proxy of reaction progression. We show a detailed evolution of the carbonate products obtained in terms of mineral phases, morphological properties, and degree of crystallinity, both as precipitate and as solid residue in the exsiccated supernatant reaction liquid.
... A Rigaku Ultima IV diffractometer was used to probe the crystal phase formed by recording PXRD profiles at a scan rate of 2°/min and 0.02° of the scanning steps. The resulting scheme is then refined by Rietveld refinement using the Chebyshev correction function with three terms (Toby 2001). To record the PXRD profile, X-rays at 40 mA (tube current), λ = 0.15405 nm, and 40 kV (tube voltage) drop on the crystalline nanosample. ...
A strong green emission is detected in a Tb³⁺-activated Ca9Bi(VO4)7 nanocrystals manufactured via the sol–gel route. Trigonal crystal prototypes with the R3c (161) space group were fabricated with unevenly shaped particles with a 41–64 nm diameter. When excited by UV radiation, the photoluminescence band exhibits a strong green-light generation at wavenumbers 18281 cm⁻¹, which is believed to be due to the ⁵D4 → ⁷F5 transition. The various energy transmission phenomena such as radiative lifetime, quantum efficiency, and non-radiative energy losses are also discussed for the synthesized nanophosphor when excited by UV radiation. The maximum observed luminescence intensity was obtained with 5.0 mol% Tb³⁺ doping when excited at 283 nm. There is a concentration quenching effect owing to the d–d exchanges. The CIE coordinates lie in the greenish domain of the chromaticity chart with a CCT value of 5937 K, thus approving their compatibility in LED fabrication for indoor lighting applications.
... X-ray powder diffraction (XRD, Cu K α radiation, Philips X'Pert Pro) was used to determine the crystal structures of the sintered samples. XRD patterns were refined using GSAS [27]. Refined parameters were lattice parameters, instrumental parameters, scale factor, sample displacement and background function. ...
In this study, the effects of different types of Mn precursors (MnO2 and Mn2O3) and sintering temperature on the defect dipole formation, ferroelectric aging and electrical properties were investigated by using Ba0.95Sr0.05TiO3 ceramics as the base. Both Mn precursors were substituted to the Ti-site as 1 mol% and two different sintering temperatures of 1325 and 1400 °C were used to study the effect of grain size. We deduced that slightly higher amounts of Mn²⁺ can be incorporated into the perovskite structure when MnO2 is used as the precursor, by using X-ray diffraction and electron paramagnetic resonance spectroscopy. Mn-doped samples sintered at 1325 °C age faster than those sintered at 1400 °C. Aging caused a decrease in the electrocaloric effect whereas Mn-doping increased it. This study shows that Mn precursor used for the acceptor doping affects the amount of Mn incorporated into the structure and therefore electrical properties of the resulting ceramics.
... Å) operated at 40 kV and 40 mA. The diffractograms were analyzed using the Rietveld method refinement with EXPGUI-GSAS software [32]. FT-IR spectra were obtained using Bruker (Vertex, 70 V) spectrophotometer, by KBr pellet (98%) method, in the spectral region of 400-4000 cm −1 , using an average of 32 scans, with a spectral resolution of 4 cm −1 . ...
In this study, L-threonine containing trivalent europium ions (LTHEu) was successfully grown through the slow evaporation method. The LTHEu single crystal exhibit well-defined facets, with dimensions around 5 × 13 × 4 mm. Structural, thermal, and spectroscopic properties were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, X-ray fluorescence (XRF), thermogravimetric analysis, differential thermal analysis, ultraviolet–visible absorption spectroscopy, and photoluminescence spectroscopy. Rietveld refinement of XRD data showed that the LTHEu crystal crystallizes in an orthorhombic system with P212121-space group. The Eu3+ ions promote an expansion effect on the unit cell volume. XRF measurements confirm the presence of the Eu3+-impurities in the L-threonine matrix. In addition, the LTHEu crystal showed thermal stability for temperatures up to 483 K. Spectroscopic analysis revealed light emission with orange color due to the combination of high-intensity bands related to 5D0→7F1 (orange) and 5D0→7F2 (red) electronic transitions of Eu3+ ions. The new emission for L-threonine crystal doped with Eu3+ observed in this study expands the range of materials with potential for application in optical devices in the visible region.
... The structural analysis was performed by powder X-ray diffraction (XRD) measurements at room temperature using a Panalytical diffractometer (Model: Empyrean) with CuK α (1.54056 Å) radiation in the 2 range between 15° and 90°. The diffraction pattern was refined by GSAS software [45] using the Rietveld method. ...
Structural, magnetic, calorimetric, and magnetocaloric properties of the GdAgGa polycrystalline intermetallic compound are reported. This compound crystallizes with an orthorhombic CeCu2-type structure. Magnetization data reveal a phase transition from a paramagnetic to a ferromagnetic state around Curie temperature (TC) = 30 K and a low-field-dependent anomaly (T*) below 14 K. Features on the time dependence of magnetic relaxation, thermomagnetic irreversibility below T*, absence of a λ-type peak on zero-field heat capacity, and the frequency dependence of imaginary and real components of ac susceptibility indicate a complex magnetic structure, in which a re-entrant spin-glass (RSG) phase coexists with long-range ferromagnetism. The RSG phase arises due to the nonmagnetic atom disorder, which induces a non-uniform ferromagnetic phase. As temperature decreases, such non-uniformity contributes to the development of spin-glass correlation. The applied external magnetic field destabilizes the RSG phase, and the magnetization increases reaching ~ 6.1 µB per Gd ion at T = 2 K for a magnetic field of 50 kOe. Isothermal magnetic entropy change (ΔSM) exhibits a broad curve with its maximum around TC and a long tail over a wide temperature range above TC. The inverse magnetocaloric effect (MCE) for T < 10 K is consistent with antiferromagnetic interactions from the RSG phase. An appreciated magnetic entropy change was observed with a maxima value of ~ 7 J/kg K and a relative cooling power of 264 J/kg for a magnetic field change of 50 kOe. The nature of the magnetic state is a critical factor influencing the GdAgGa compound magnetocaloric effect.
... A good agreement for Rietveld refinement results if the χ 2 (goodness of fit) factors around the 1.206-1.296. According to Toby, the value of χ 2 (chi-squared) is allowed to a maximum of 1.3 [33]. The values in this range provide an Table 1 show that the χ 2 factor is within the range of a good agreement, and the value of the R factor is very small, where this value is also one of the criteria showing good agreement in the Rietveld analysis. ...
Magnetic and microwave absorbing properties of cerium-substituted zinc ferrite synthesized using the milling technique have been studied. Cerium substituted on zinc ferrite was synthesized from ZnO, Ce2O3, and Fe2O3 powders in a mole ratio to the form of ZnCexFe(2−x)O4 (x = 0.01 up to 0.05) by solid-state reaction. The mixture of these compounds was milled using the high energy milling (HEM) technique and sintered at 1200 °C for 5 h. The identification result of the XRD shows that all samples are a single phase that follows the structure of ZnFe2O4. The TEM (Transmission Electron Microscope) image of ZnCexFe(2−x)O4 powders show that all samples have homogenous morphology but not uniform powder with particle sizes of about 100–500 nm. The magnetic properties of the samples were analyzed using a vibrating sample magnetometer (VSM). The result shows ferromagnetic behavior, with the Ms value around 19.37 up to 8.03 emu/g and the Hc value around 134–324 Oe. Microwave absorption ability was measured using VNA (Vector Network Analyzer), and their results indicated that the RL curve was deeper with increasing Ce³⁺ ions concentration. The best RL shows the ZnCexFe(2−x)O4 sample with a value of x = 0.05, i.e., 17.62 dB at a frequency of 10.76 GHz. It means that ZnCe0.5Fe1.95O4 powder can absorb microwaves at 98.26% at a frequency of 10.76 GHz.
... A PXRD circuit was formed using CuKα radiation with 0.15405 nm wavelength, tube current (40 mA), and tube voltage (40 kV) to generate X-rays. The three-term Chebyshev correction function was utilized to refine the background in GSAS [23,24]. ...
A series of Ca9Gd(VO4)7: Dy³⁺ (x = 0.01–0.20) nanophosphor crystals emitting a cool white light were synthesized by solution combustion methodology. The X-ray diffraction patterns were analyzed and processed using Rietveld refinement. The fabricated nanophosphor was found to crystallize in a trigonal crystal lattice with space group R3c(161). The morphological behavior of the prepared nanophosphor was investigated using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The photoluminescence properties of the nanophosphor correspond to cool white emission upon near-ultraviolet (NUV) excitation at 327 nm due to ⁴F9/2 → ⁶H15/2 (bluish) and ⁴F9/2 → ⁶H13/2 (yellowish) radiative relaxations at 487 nm and 576 nm respectively. Also, there is a strong occurrence of double charge transfer from O²⁻ ions to Dy³⁺ and V⁵⁺ ions with the latter being stronger due to the high positive charge of V⁵⁺ ions. Color coordinates (x = 0.2878, y = 0.3259) are consistent with white emission. Auzel's model was implemented to examine the non-radiative relaxation (113.5 ms⁻¹), radiative lifetime (1.4856 ms), and quantum efficiency (83.13%) values. The crystalline and optical behavior of the synthesized cool white emitting nanophosphor facilitates its use in near-UV-based WLEDs and other advanced solid-state lighting.
... These findings are in line with results reported by other publications in the literature [2,40]. The XRD data were refined with the application of the Rietveld method using the GSAS program, EXPGUI package [32,41], and the crystal structures were visualised using the VESTA program [32,42]. ...
Monovalent-doped Pr0.75Na0.05K0.20Mn1–xFexO3 (x = 0–0.04) manganites were prepared using conventional solid-state reaction method to study the effect of Fe³⁺ substitution on magnetic and electrical properties and magnetoresistance (MR) effect. An X-ray diffraction measurement analysed using the Rietveld refinement method revealed that all the samples crystallised in orthorhombic structure with Pnma space group with a slight increase in unit cell volume from 230.44 (x = 0) to 231.27 Å (x = 0.04). Fe substitution at x = 0.02 reduced metal–insulator transition temperature from 122 (x = 0) to 80 K. At x = 0.04, the sample exhibited insulating properties in the whole measured temperature region, indicating a weakened double exchange mechanism. The decrease of Curie temperature, TC for all samples from 140.73 (x = 0) to 131.59 K (x = 0.02) and 126.87 K (x = 0.04) indicates weakened ferromagnetic interaction between Mn ions, which may be due to competition between antiferromagnetic and ferromagnetic interaction in the Fe-substituted samples. The increase in hopping energy is attributed to the reduction of available hopping sites because of the reduction of Mn³⁺ concentration due to Fe substitution. Fe substitution improved intrinsic MR as evidenced by the increase of MR peak value from 22 to 40% for x = 0 and x = 0.02, respectively, while high concentration of Fe at x = 0.04 increased the extrinsic MR effect. The findings indicate that the MR behaviour can be tuned from intrinsic to extrinsic MR because of Fe substitution at the Mn site.
Graphical abstract
The present work reports the antitumor activity and a comprehensive study of the Cu(II) complex with 1,10-phenanthroline and l-tyrosine, synthesized by slow solvent evaporation method. X-ray powder diffraction (XRPD) showed that the complex crystallizes in a monoclinic structure with P21/c-space group. All IR- and Raman-active bands were assigned and vibrational properties were evaluated under solvation effects from quantum chemical calculations using density functional theory (DFT). Additionally, optimized geometry, electrostatic potential surface, spatial distribution, and energies of molecular orbitals HOMO and LUMO, as well as chemical reactivity indexes, were obtained using PBE1PBE theoretical level. Antitumor activity of the complex was evaluated through cytotoxic tests in vitro in tumor cell lines PC3 and SNB-19, presenting IC50 equal to 1.5 μM and 2.9 μM, respectively. Additionally, ADME parameters were evaluated to study the drug-like properties of the synthesized complex. Therefore, our findings suggest that the complex presents a promising antitumor activity, with the potential to be used in cancer chemotherapy treatment.
Subducting sedimentary layer typically contains water and hydrated clay minerals. The stability of clay minerals under such hydrous subduction environment would therefore constraint the lithology and physical properties of the subducting slab interface. Here we show that pyrophyllite (Al2Si4O10(OH)2), one of the representative clay minerals in the alumina-silica-water (Al2O3-SiO2-H2O, ASH) system, breakdowns to contain further hydrated minerals, gibbsite (Al(OH)3) and diaspore (AlO(OH)), when subducts along a water-saturated cold subduction geotherm. Such a hydration breakdown occurs at a depth of ~135 km to uptake water by ~1.8 wt%. Subsequently, dehydration breakdown occurs at ~185 km depth to release back the same amount of water, after which the net crystalline water content is preserved down to ~660 km depth, delivering a net amount of ~5.0 wt% H2O in a phase assemblage containing δ-AlOOH and phase Egg (AlSiO3(OH)). Our results thus demonstrate the importance of subducting clays to account the delivery of ~22% of water down to the lower mantle.
Carbonates are viewed as the principal oxidized carbon carriers during subduction, and thus the stability of subducted carbonates has significant implications for the deep carbon cycle. Here we investigate the high pressure-temperature behaviors of rhodochrosite in the presence of iron up to ∼34 GPa by in-situ X-ray diffraction and ex-situ Raman spectroscopy. At relatively low temperature below ∼1 500 K, MnCO3 breaks down into MnO and CO2. Upon heating to ∼1 800 K, however, the MnCO3-Fe0 reactions occur with the formation of Mn3O4, FeO and reduced carbon. A ‘three-stage’ reaction mechanism is proposed to understand the kinetics of the carbon-iron-manganese redox coupling. The results suggest that Fe0 can serve as a reductant to greatly affect the stability of rhodochrosite, which implies that the effect of Fe-metal should be seriously considered for the high pressure-temperature behaviors of other predominant carbonates at Earth’s mantle conditions, particularly at depths greater than ∼250 km.
Materials with low thermal conductivity usually have complex crystal structures. Herein we experimentally find that a simple crystal structure material AgTlI2 (I4/mcm) owns an extremely low thermalconductivityof0.25W/mK at room temperature. To understand this anomaly, we perform in-depth theoretical studies based on ab initio molecular dynamics simulations and anharmonic lattice dynamics. We find that the unique atomic arrangement and weak chemical bonding provide a permissive environment for strong oscillations of Ag atoms, leading to a considerable rattling behaviour and giant lattice anharmonicity. This feature is also verified by the experimental probability density function refinement of single-crystal diffraction. The particularly strong anharmonicity breaks down the conventional phonon gas model, giving rise to non-negligible wavelike phonon behaviours in AgTlI2 at 300 K.
Intriguingly, unlike many strongly anharmonic materials where a small propagative thermal conductivity is often accompanied by a large diffusive thermal conductivity, we find an unusual coexistence of ultralow propagative and diffusive thermal conductivities in AgTlI2 based on the thermal transport
unified theory. This study underscores the potential of simple crystal structures in achieving low thermal conductivity and encourages further experimental research to enrich the family of materials with ultralow thermal conductivity.
The evolution of metallurgy is a fundamental aspect related to the knowledge of the technological level of ancient civilizations, for which the information was mostly part of an oral tradition. The ancient, preserved artefacts are the only keepers of this long gone knowledge. Most advanced non-invasive techniques provide us the key to access it. Neutron techniques are nowadays the only available approach for revealing, non-destructively and with good spatial resolution, the morphological and microstructural properties within the whole volume of densely composed artefacts such as bronze statues. Application of neutron methods allows us to learn about ancient artefact manufacturing methods and to study at a very detailed level the current conservation status in their different parts. As part of a research project dedicated to the study of ancient Asian bronzes led by the Rijksmuseum Metal Conservation Department, four statues from the Rijksmuseum Asian collection were analysed using non-invasive neutron techniques. In this work, we present the investigation of a South Indian bronze statuette depicting Shiva in the form of Chandrasekhara (AK-MAK-1291, c. 1000–1200 A.D.) by means of white beam tomography, energy-selective neutron imaging (performed on CONRAD-2 at HZB, DE, and on FISH at TU-Delft, NL), and neutron diffraction (on ENGIN-X at ISIS, UK). The application of neutron imaging revealed the inner structure of the statue and allowed us to investigate the conservation state and potential cracking on the surface and in the bulk, to understand the interconnection of the different sections of the statue, and to obtain clues about the manufacturing processes. These morphological and microstructural results were employed to guide neutron diffraction analyses that allowed us to precisely characterize compositional differences, the presence of dendrites and columnar growth peak structures related to casting. This work is a complete non-invasive analytical investigation on an archaeological bronze artefact, providing outstanding results: from a quantitative analysis of the composition and microstructure to an in-depth morphological analysis capable of unveiling details on the ancient casting methods of the statue.
Electrical resistivity measurements on oriented FeTiO3 ilmenite using single crystals at high pressures proves that FeTiO3 ilmenite shows anisotropic electrical resistivity. The resistivity in the direction perpendicular to the c-axis decreased monotonously with increasing pressure. In contrast, the resistivity in the parallel direction to the c-axis initially decreased and slightly increased with increasing pressure above 6 GPa. It then resumed decreasing above 8 GPa. The hallow-shape of the curvature was observed. Neutron and synchrotron X-ray diffraction experiments provided an accurate picture of the pressure-induced changes of the FeTiO3 ilmenite structure. FeTiO3 transforms neither into perovskite nor LiNbO3 phase under pressures up to 28 GPa. However, different compression curves were observed for both FeO6 and TiO6 octahedra below 8 GPa. FeO6 is more compressible and flexible than TiO6. Among Fe–Fe, Ti–Ti and Fe–Ti interatomic distances, the shortest Fe–Ti distance presents the highest electrical restivity and electron mobility according to Fe²⁺Ti⁴⁺ and Fe³⁺Ti³⁺ by electron super-exchange mechanism, which is enhanced during compression. At high pressure, the electron configuration of Fe²⁺ (3d⁶) is more strongly changed than Ti⁴⁺ (3d⁰) and the former cation is the emphasized by Jahn–Teller effect in the ligand field of C3v molecular symmetry. The anisotropic electrical resistivity and non-uniform structure change of Fe–Ti interatomic distance can be explained by possible spin transition. The spin transition of FeKβ from high-spin to intermediate-spin state is possible in the electronic state change of FeTiO3.
Nickel-rich LiNixCoyMn1−x−yO2 cathode materials have been studied to increase the energy density of lithium-ion batteries due to their high capacity and low cost. However, the complex side reaction in the electrode/electrolyte interphase and cracks inside the secondary particles would decrease the stability of crystalline structure and interface, which further affects the cycling life. Here, a thermodynamically stabilized interface was constructed on the surface of single crystalline nickel-rich cathode material via an acid solution treatment. Structural characterization results confirm the enhanced structural reversibility during electrochemical cycling. Electrochemical data suggests accelerated kinetics for lithium ion diffusion process after treatment. Consequently, modified nickel-rich material delivers significantly enhanced capacity from 131.0 mAh/g for pristine material to 266.2 mAh/g at 0.1 C rate and improved cycling stability. These results suggest it is a moderate method for optimizing the available capacity of high-Ni cathode materials.
Graphical Abstract
Recently, topological insulators (TIs) KHgX (X = As, Sb, Bi) with hourglass-shaped dispersion have attracted great interest. Different from the TIs protected by either time-reversal or mirror crystal symmorphic symmetry tested in previous experiments, these materials were proposed as the first material class whose band topology relies on nonsymmorphic symmetries. As a result, KHgX shows many exotic properties, such as hourglass-shaped electronic channels and three-dimensional doubled quantum spin Hall effects. To date, high-pressure experimental studies on these nonsymmorphic TIs are minimal. Here, we carried out high-pressure electrical measurements up to 55 GPa, together with high-pressure X-ray diffraction measurements and high-pressure structure prediction on KHgAs. We found a pressure-induced semiconductor-metal transition between ~16 and 20 GPa, followed by the appearance of superconductivity with a Tc of ~3.5 K at approximately 21 GPa. The superconducting transition temperature was enhanced to a maximum of ~6.6 K at 31.8 GPa and then slowly decreased until 55 GPa. Furthermore, three high-pressure phases within 55 GPa were observed, and their crystal structures were established. Our results showed the high-pressure phase diagram of KHgAs and determined the pressure-induced superconductivity in nonsymmorphic TIs. Thus, our study can be used to facilitate further research on superconductivity and topologically nontrivial features protected by nonsymmorphic symmetries.
The Li-excess disordered rock salt cathode material, Li1.2Ni0.2Ti0.6O2, was synthesized via the sol–gel method to investigate the impact of different sintering temperatures on its structure, morphology, and electrochemical performance. X-ray diffraction (XRD) analysis revealed a cubic rock salt structure for the material. Raman spectroscopy indicated the presence of short-range-ordered domains of Li2TiO3 and LiNiO2 in the samples. The XPS results confirmed the existence of an oxygen vacancy structure on the sample’s surface. Morphological observations demonstrated that micron-scale secondary particles agglomerated with nanoscale primary particles, resulting in a nano-microstructure formation. Electrochemical testing conducted at room temperature within a voltage range of 1.5 ~ 4.8 V showed that the sample sintered at 600 °C exhibited the highest specific discharge capacity of approximately 304.4 mAh g⁻¹ at 20 mA g⁻¹. The influence of surface structure on electrochemical properties in disordered rock salt cathode materials is elucidated through interactions between small primary particles and surface oxygen vacancies.
A solid-phase metallurgy combined with spark plasma sintering technology was used to prepare U3Si2 pellets. The thermal conductivity and oxidation behavior of the pellets were studied. The pellets were highly dense (> 98% theoretical density) and had an ultra-high phase purity. The thermal conductivity of the U3Si2 pellets increased linearly with temperature from 300 to 973 K. By further annealing the pellets at 300 °C in air for two hours, the oxidation onset temperature was increased from 490 to 520 °C. A mechanism of pore passivation was proposed to account for the enhanced oxidation resistance.
The current manuscript deals with the magnetic property changes induced by substituting nickel in place of cobalt in Co2TiO4 by preparing the samples from a single-step calcination process. Monophasic cubic spinels bearing the compositions Co1.80Ni0.20TiO4, Co1.40Ni0.60TiO4, and CoNiTiO4 were formed, and higher nickel contents of more than 50 mol% in Co2–2xNi2xTiO4 resulted in biphasic products consisting of spinel and NiO. The successful structural refinements of the X-ray diffraction patterns in the Fd-3 m space group revealed a gradual decrease in the lattice parameter with increasing nickel content. Raman spectra augmented the stabilization of cubic spinel, exhibiting all the fingerprint modes. Optical transitions corresponding to Ti³⁺, Co²⁺, and Ni²⁺ were noted in the UV–visible spectra of nickel-substituted samples. XPS analysis of CoNiTiO4 confirmed the presence of Co²⁺, Ni²⁺, Ti⁴⁺ (77%), and Ti³⁺ (23%). Both the temperature and field-dependent magnetic measurements were performed on the nickel-substituted samples. While Co1.80Ni0.20TiO4, Co1.40Ni0.60TiO4 remained paramagnetic at 100 K, CoNiTiO4 showed ferromagnetic ordering. At 2 K, all three samples showed ferromagnetic hysteresis. In the temperature-dependent measurements, all samples show divergence in the zero field-cooled and field-cooled conditions, showing negative magnetization. Higher magnetic fields shifted the temperature at which the divergence occurred in the case of CoNiTiO4. The spin-only magnetic moment values decreased due to the gradual increase in nickel content, which had weaker magnetizing power than cobalt.
In this paper, the results of studying the formation conditions, crystal structure, thermal, spectral, and optical properties, as well as the electronic band structure of cobalt-doped zinc glycolate Zn1 − xCox(OCH2CH2O) (0˂x ≤ 0.2) are presented. Using X-ray powder diffraction data, it was shown that solid solutions are obtained by partial substitution of cobalt for zinc, while maintaining the crystal structure of Zn(OCH2CH2O). The vibrational spectra of Zn1 − xCox(OCH2CH2O) are identical to those of Zn(OCH2CH2O) and correlate completely with the results of structural analysis. As a result of heating in air at 600–900 °C, glycolate Zn1xCox(OCH2CH2O), where 0˂x ≤ 0.1, turns into oxide of the composition Zn1 − xCoxO with wurtzite structure, whose powders have a deep green color (Rinman’s green). The UV-Vis-NIR spectra of Zn1 − xCoxO contain bands typical of Co2+ ion transitions in the tetrahedral environment. When Zn1 − xCox(OCH2CH2O) is heated in helium atmosphere, composites (1-x)ZnO:xCo:nC are formed that include a phase with wurtzite structure, metallic cobalt, and elemental carbon. The electronic band structure, optical characteristics, and isosurfaces of wave functions of pure and cobalt-doped zinc glycolate and oxide were calculated. This allowed us to establish the reasons for the increase in the band gap width in glycolate compared to the oxide and its decrease during doping.
The low-temperature thermoelectric performance of Bi-rich n-type Mg3(Bi,Sb)2 was limited by the electron transport scattering at grain boundaries, while removing grain boundaries and bulk crystal growth of Mg-based Zintl phases are challenging due to the volatilities of elemental reactants and their severe corrosions to crucibles at elevated temperatures. Herein, for the first time, we reported a facile growth of coarse-grained Mg3Bi2-xSbx crystals with an average grain size of ~800 μm, leading to a high carrier mobility of 210 cm² · V⁻¹ · s⁻¹ and a high z of 2.9 × 10−3 K⁻¹ at 300 K. A Δ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta$$\end{document}T of 68 K at Th of 300 K, and a power generation efficiency of 5.8% below 450 K have been demonstrated for Mg3Bi1.5Sb0.5- and Mg3Bi1.25Sb0.75-based thermoelectric modules, respectively, which represent the cutting-edge advances in the near-room temperature thermoelectrics. In addition, the developed grain growth approach can be potentially extended to broad Zintl phases and other Mg-based alloys and compounds.
Strong green-emission is observed in the new Tb3+ activated Sr6Y2Al4O15 nanocrystalline material series fabricated via solution combustion methodology. A monoclinic crystal framework with space group I4/mcm (140) having irregularly shaped grains with an average size of 49 nm is formed. Morphological aspects are examined via scanning and transmission electron microscopy (SEM and TEM). On near-UV excitation, the photoluminescence spectrum presents a fair green-light production at 18382 cm-1 wavenumbers reliable with the 5D4→7F5 electronic transition. The energy transfer phenomena are also discussed. The highest luminous intensity is observed for 5.0 mol% of Tb3+ composition with 282 nm excitation wavelength. d-d exchanges authorized the presence of the concentration quenching phenomenon. Diffuse reflectance spectroscopy was taken into use to explore the energy band gap which lies in the semiconductor domain. The CIE coordinates lay in the greenish zone of the chromaticity scheme, thus confirming their latent contention in pc-WLED fabrication and other advanced photonic applications.
Strong green-emission is observed in the new Tb3+ activated Sr6Y2Al4O15 nanocrystalline material series fabricated via solution combustion methodology. A monoclinic crystal framework with space group I4/mcm (140) having irregularly shaped grains with an average size of 49 nm is formed. On near-UV excitation, the photoluminescence spectrum presents a fair green-light production at 18382 cm-1 wavenumbers reliable with the 5D4→7F5 electronic transition. The CIE coordinates lay in the greenish zone of the chromaticity scheme, thus confirming their latent contention in pc-WLED fabrication and other advanced photonic applications.
In this study, two ionic modification strategies on trirutile MgTiTa2O8 ceramics, including Mg site non-stoichiometry (Mg1+xTiTa2O8) and (Al1/2Nb1/2)⁴⁺ ionic doping (MgTi1−y(Al1/2Nb1/2)yTa2O8), were adopted to improve the microwave dielectric properties. The results show that a small doping content does not change the crystal structure type, indicating that the trirutile MgTiTa2O8 solid solutions can be formed. On the one hand, the increase of sintering decreases the porosities of microstructures, which benefit the dielectric constant and Q×f value; however, excessive sintering temperature leads to abnormal growth of grain, deteriorating the uniformity of grain growth and then increases the dielectric loss. On the other hand, the variations of the dielectric constant are dominated by the ionic polarizability intrinsically, while the Q×f value is positively correlated with the packing fraction value. The two modification strategies both benefit the Q×f value with improvements of about 21% and 30% in Mg1+xTiTa2O8 and MgTi1−y(Al1/2Nb1/2)yTa2O8 ceramics, respectively. In summary, excellent microwave dielectric properties of MgTi1−y(Al1/2Nb1/2)yTa2O8 (y = 0.10) system are obtained when sintered at 1350 °C: εr = 43.58, Q×f = 24,565 GHz, τf = 100.37 ppm/°C.
Herein, the 0.725BiFeO3−0.275BaTi1−xHfxO3 + 1 mol% MnO2 ceramics (x = 0, 0.01, 0.05, 0.10; abbreviated as 0Hf, 0.01Hf, 0.05Hf, 0.10Hf, BF-BTH) were prepared with the conventional technique. Pure perovskite structure of the BF-BTH was obtained with the R and T phases. The bond length and bond angle of ceramics enlarged when doped by Hf, resulting in a distorted structure of the R phase. The introduction of Hf increased the content of the R phase and structural distortion, leading to the enhanced remanent polarization from 14.7787 µC/cm² for 0Hf to 23.0335 µC/cm² for 0.10Hf. Therefore, although the coercive field gradually increased, the piezoelectric response was not significantly deteriorated. The d33 value of the BF-BTH showed higher values (130 pC/N to 116 pC/N) over a wide range of components ranging from x = 0 to 0.10. Furthermore, Hf⁴⁺ effectively reduced the dielectric loss of ceramics (~ 15.6%). Hf⁴⁺-doped BiFeO3-based ceramics provided a clue for reducing dielectric loss and keeping the piezoelectric properties with a wide range of components.
Inorganic sulfide solid-state electrolytes, especially Li6PS5X (X = Cl, Br, I), are considered viable materials for developing all-solid-state batteries because of their high ionic conductivity and low cost. However, this class of solid-state electrolytes suffers from structural and chemical instability in humid air environments and a lack of compatibility with layered oxide positive electrode active materials. To circumvent these issues, here, we propose Li6+xMxAs1-xS5I (M=Si, Sn) as sulfide solid electrolytes. When the Li6+xSixAs1-xS5I (x = 0.8) is tested in combination with a Li-In negative electrode and Ti2S-based positive electrode at 30 °C and 30 MPa, the Li-ion lab-scale Swagelok cells demonstrate long cycle life of almost 62500 cycles at 2.44 mA cm⁻², decent power performance (up to 24.45 mA cm⁻²) and areal capacity of 9.26 mAh cm⁻² at 0.53 mA cm⁻².
We present chemical and mineralogical data on a megacryst of a unique carbonate-bearing fluorapatite from altered Tertiary volcanics of the Veneto Volcanic Province (VVP) in the western Lessini Mountain range (Veneto, northern Italy). The cm-sized specimen was identified and characterized by scanning electron microscope (SEM), X-ray powder diffraction (XRPD), micro-Raman spectroscopy and electron probe microanalyses. Major and trace elements of the carbonate-bearing fluorapatite are consistent with the crystallization at depth from a nelsonitic melt or an evolved alkaline melt derived from a mantle source metasomatized by carbonate-rich fluids. The Sr and Nd isotopic composition fits with the lavas and xenoliths from the VVP showing a DM-HIMU affinity with addition of a crustal, possibly carbonate, component. Our data are in agreement with a recent geodynamic model for the hybridization of the VVP mantle triggered by breakdown of carbonates within the subducting Tethyan oceanic slab. Cronstedtite, chabazite-Ca, calcite associated with reaction rims of amphibole and secondary carbonate-rich fluorapatite within the megacryst originated from low temperature hydrothermal alteration of the volcanics. Cronstedtite is the first occurrence in the VVP area.
Cerium is the most abundant metal of rare-earth elements. It can be used to make materials such as phosphors and alloys, that have applications in various applied fields (like electronics, magnetics and heterogeneous catalysis) and devices (like catalytic converters and gas mantles). Cerium-Based Materials: Synthesis, Properties and Applications presents detailed knowledge about cerium materials. Starting with the history of cerium-based materials, it gives an introduction to the synthesis of chemicals like cerium oxides and composites. This is followed by information about characterization of cerium nanoparticles and industrial applications of cerium-based materials, with a focus on catalysis, biomedical engineering and pharmaceutical chemistry. This book is an essential reference for researchers and chemical engineers who want a summary of cerium materials and its applications.
In this work, A-site Nd doped BaTiO3 ceramics in the form of Ba1−xNd2x/3TiO3 with a wide substitution level range of x = 0–0.2 have been prepared via solid-state reaction method. Powder X-ray diffraction results reveal that Nd is completely incorporated into the BaTiO3 lattice in all specimens. Further analyses based on Rietveld refinement suggest that tetragonal and pseudo-cubic phases coexist in Ba1−xNd2x/3TiO3 ceramics with x ≤ 0.06, and the amount of tetragonal phase is raised with the increase of x value. When x value is larger than 0.08, only pseudo-cubic is observed. The generated \(V^{\prime\prime}_{{{\text{Ba}}}}\), \({\text{Nd}}_{{{\text{Ba}}}}^{\cdot }\) and \(V_{{\text{O}}}^{{\cdot \cdot }}\) defects, which are identified by X-ray photoelectron spectra, make the grain size displays a tendency of decrease first mainly due to the pining effect, and then increase ascribed to the accelerate of mass diffuse. By introducing such wide range of substitution level, Ba1−xNd2x/3TiO3 ceramics with colossal dielectric constant (x = 0.08), temperature-stable dielectric properties (x = 0.15), especially relaxor behavior (x = 0.20) noticed for the first time, are, respectively, received, which is closely related to the variation of phases and defects induced by the addition of Nd. This study may provide a special idea to modify BaTiO3 to satisfy diversified applications by single element with a wide doping range, and could lay the foundation of future works focusing on the various potential applications of Ba1−xNd2x/3TiO3 ceramics.
A novel low-fired NaCaLa(MoO4)3 ceramic was synthesized via a conventional solid-state reaction method. The sintering behavior, phase structure, morphology, and microwave dielectric properties of ceramic were systematically investigated. NaCaLa(MoO4)3 compound was confirmed to be a single-phase with a tetragonal scheelite structure of I41/a space group. The sintering temperature will affect the cationic ordering of NaCaLa(MoO4)3 ceramics, thereby affecting the quality factor. NaCaLa(MoO4)3 ceramics exhibited a high relative density above 98% in the all sintering ranges, especially the maximum relative density reached 98.34%. The theoretical dielectric constant and packing fraction were calculated based on the refined parameters. The calculations for the chemical bonds of NaCaLa(MoO4)3 ceramics show that NaCaLa–O bond and Mo–O bond have the upper hand in dielectric constant and quality factor, respectively. NaCaLa(MoO4)3 ceramic sintered at 825 °C demonstrates foremost microwave dielectric properties with low εr = 10.72, high Q × f = 49,495 GHz, and τf = − 49 ppm/°C. Momentously, NaCaLa(MoO4)3 ceramic had a good compatibility with Ag powder, suggesting that it is a potential candidate for LTCC applications.
The dielectric ceramics of Ca1−xCuxSiO3 (x = 0 − 0.025) were prepared by solid-phase reaction method. The effects of Cu doping on phase composition, crystal structure, and dielectric properties of CaSiO3 ceramics were investigated. XRD results indicated that appropriate content of Cu doping could suppress impurity phases and obtain pure α-CaSiO3 calcined powders. After sintering, α-CaSiO3 phase was the main phase accompanied with a small quantity of impurity phases in undoped ceramics, which transformed to the single β-CaSiO3 phase after Cu doping. The phase transformation could be attributed to the change of the geometric position of SiO4 tetrahedron. SEM images showed that grain morphology changed from irregular and loose particles to dense lath by Cu doping. The Ca0.985Cu0.015SiO3 ceramics sintered at 1125 °C exhibited excellent dielectric properties: εr = 5.22, Q × f = 18,948 GHz, τf = − 63 ppm/°C, and these make the ceramics promising for use in microwave applications.
A key strategy to design environmental barrier coatings focuses on doping multiple rare-earth principal components into β-type rare-earth disilicates (RE2Si2O7) to achieve versatile property optimization. However, controlling the phase formation capability of (nRExi)2Si2O7 remains a crucial challenge, due to the complex polymorphic phase competitions and evolutions led by different RE 3+ combination. Herein, by fabricating twenty-one model (REI0.25 REII0.25REIII0.25REIV0.25)2Si2O7 compounds, we find that their formation capability can be evaluated by the ability to accommodate configurational randomness of multiple RE 3+ cations in β-type lattice while preventing the β-to-γ polymorphic transformation. The phase formation and stabilization are controlled by the average RE 3+ radius and the deviations of different RE 3+ combinations. Subsequently, based on high-throughput density-functional-theory calculations, we propose that the configurational entropy of mixing is a reliable descriptor to predict the phase formation of β-type (nRExi)2Si2O7. The results may accelerate the design of (nRExi)2Si2O7 materials with tailored compositions and controlled polymorphic phases.
Cubic energy materials such as thermoelectrics or hybrid perovskite materials are often understood to be highly disordered1,2. In GeTe and related IV–VI compounds, this is thought to provide the low thermal conductivities needed for thermoelectric applications¹. Since conventional crystallography cannot distinguish between static disorder and atomic motions, we develop the energy-resolved variable-shutter pair distribution function technique. This collects structural snapshots with varying exposure times, on timescales relevant for atomic motions. In disagreement with previous interpretations3–5, we find the time-averaged structure of GeTe to be crystalline at all temperatures, but with anisotropic anharmonic dynamics at higher temperatures that resemble static disorder at fast shutter speeds, with correlated ferroelectric fluctuations along the <100>c direction. We show that this anisotropy naturally emerges from a Ginzburg–Landau model that couples polarization fluctuations through long-range elastic interactions⁶. By accessing time-dependent atomic correlations in energy materials, we resolve the long-standing disagreement between local and average structure probes1,7–9 and show that spontaneous anisotropy is ubiquitous in cubic IV–VI materials.
The main objective is to prepare cerium containing aluminium-free siliceous MCM-22 (AF-CeMCM-22) catalyst by in-situ hydrothermal method, its characterization, and catalytic application for the conversion of biomass model components. Powder XRD, FTIR, and BET surface area were used to study the microstructure of the samples. The powder XRD patterns showed a distinguished MCM-22 framework structure with a uniform dispersion of cerium ions in the MCM-22 framework. SEM images of the cerium AF-CeMCM-22 showed a spherical morphology formed out of platelet flakes which have a surface area in the range of 173-145 m2g1. 29Si NMR and DR-UV-Vis studies confirmed the well-condensed nature of the silica framework in MCM-22 and the presence of cerium ions as Ce(IV) in the extra framework environment. The resultant AF-CeMCM-22 was found to be a promising catalyst for the conversion of isoeugenol to vanillin at 60 ℃ in presence of H2O2 (oxidant) with a selectivity of 71%. Further, the activity is retained for several cycles.
Background
Zeolites and zeolite like microporous materials are well known as potential heterogeneous acid catalysts, whose discovery has made a significant impact in the petroleum, petrochemical and fine chemical industries. ]. In recent years, zeolite, zeolites like molecular sieves, and inorganic oxide-based heterogeneous catalysts played a significant role in biomass valorization to receive value-added chemicals. Thus we focused on utilization of zeolite for biomass transformation.
Objective
Preparation of Cerium containing aluminium-free siliceous MCM-22 (AF-CeMCM-22) by the in-situ hydrothermal method and explore its importance on biomass transformation.
Method
Powder XRD, FTIR and BET surface area were used to study the microstructure of the samples. SEM and FE-SEM were used to study morphology, TGA was used to evaluate the thermal stability, and 29Si NMR and DR-UV-Vis were used to study the environment of the MCM-22 framework. The prepared and confirmed material was used for the oxidation of levulinic acid over the liquid phase setup. Gas chromatography was used to evaluate the catalytic study, such as conversion and selectivity; also, GCMS was used for the confirmation of products.
Low-temperature and low-field magnetocaloric materials with high magnetocaloric effect (MCE) performance have important prospects in applications such as gas liquefaction. A series of polycrystalline Er1−xYxCr2Si2 (0 ≤ x ≤ 0.8) samples were successfully synthesized by arc melting, showing giant low-field MCE. For the sample with x = 0.1, the compound shows the best MCE performance, with the appropriate working temperature down to 2 K. Furthermore, the maximum value of magnetic entropy change ((−ΔSM)max) and adiabatic temperature change ((ΔTad)max) under the field change of 0–1 T are calculated to be 19.2 J kg−1 K−1 and 4.3 K correspondingly. The value of (−ΔSM)max is the largest ever reported for intermetallic MCE materials below 20 K. The characteristic of magnetic phase transition is verified to be of second order on basis of Arrott plots, mean field theory and rescaled universal −ΔSM curves. The physical mechanism indicates that the great enhancement of (−ΔSM)max as large as 15.9% due to 10% Y substitution originates from the larger saturation magnetic moments and the smaller saturated magnetic fields.
P2-Na0.67Mn0.5Fe0.5O2 has been thought to be one of the potential cathode materials for sodium-ion batteries because of its economic efficiency and high specific capacity (260 mAh g⁻¹). However, its practical applicability was limited by rapid capacity degradation and poor rate performance. In this work, the Spherical Ce-modified Na0.67Mn0.5Fe0.5O2 materials were successfully synthesized by the hydrothermal method, which simultaneously realized Ce doping and CeO2 coating. During the high-temperature calcination process, a section of Ce was doped into the lattice, and the stronger Ce–O bonding reduces the TMO2 layer spacing and enhanced the structural stability of the material, in addition, the larger radius of Ce⁴⁺ provides a larger interlayer gap for the diffusion of sodium ions and reduces the migration potential of Na⁺. The other section of Ce was coated on the material surface in the form of CeO2, which protects the electrode from electrolyte erosion and avoids side reactions. Electrochemical tests demonstrated that the 3 wt% Ce-modified FM sample (FM-3) displays good cycling performance and rate capability, with a capacity retention of 61.8% after 100 cycles at 1 C, compared to just 52.6% for the pristine sample (FM-0). Even at 2 C, the FM-3 has a discharge-specific capacity of 99.7 mAh g⁻¹, whereas FM-0 only has 79.6 mAh g⁻¹. An efficient modification technique for creating high-performance sodium-ion battery cathode materials is presented in this work.
The effects of non-stoichiometry on the phase composition, crystal structure, and dielectric properties of Mg2 + xAl4 + ySi5 + zO18 ceramics were systematically studied. The stoichiometry deviation of Mg2 + xAl4 + ySi5 + zO18 ceramics leads to a change in the [MgO6] oxygen octahedron and symmetry of crystal structure, which has a significant impact on their dielectric properties. The theoretical polarizability improves linearly with the increase of stoichiometric ratio deviation, resulting in a slight increase of permittivity from 4.93 to 5.08. The center symmetry of the [(Si4Al2)O18] hexagonal ring in Mg2 + xAl4 + ySi5 + zO18 ceramics plays a crucial role in determining the Q×f value. The enhanced center symmetry of [(Si4Al2)O18] hexagonal ring from asymmetric structure to centrosymmetric structure improves the Q×f values of Mg2 + xAl4 + ySi5 + zO18 ceramics. The reduction of τf value is correlated to the decrease of Mg–O bond value and the increase of [MgO6] oxygen octahedral distortion. The Mg2.2Al4Si5O18 ceramic presents excellent dielectric properties at 1440 °C for 4h: εr = 4.97, Q×f = 100,268 GHz, and τf = −12.07ppm/ °C.
BaTi1-x(Sb0.5Nb0.5)xO3 ceramics (0.01 ≤ x ≤ 0.3) were prepared by solid-state reaction method. The effect of co-substituting Ti4+ with Sb3+ and Nb5+ on its crystal structure, microstructure, and dielectric properties was studied. When 0.01 ≤ x ≤ 0.1, a single-phase barium titanate solid solution can be obtained; when 0.15 ≤ x ≤ 0.25, a small amount of unknown second phase was appeared; and when the composition (x) increases to 0.3, a large amount of unknown second phases are precipitated. The main crystal phase of BaTi1-x(Sb0.5Nb0.5)xO3 ceramics has a change of tetragonal to cubic with the increase of x. As x increases from 0.1 to 0.25, the dielectric constant decreases from 1264 to 214, the dielectric loss decreases from 0.253% to 0.046% (1 MHz, 25 °C), the capacitance temperature coefficient changes from − 7897 to − 1657 ppm/ °C, and the insulation resistivity is greater than 1012 Ω cm. This means that BaTi1-x(Sb0.5Nb0.5)xO3 (x = 0.1 ~ 0.25) ceramics can be suitable for temperature-compensated ceramic capacitors.
We report on sintering, structural, morphological, electrical, and magnetic characterization of the superconducting FeSe0.88. The sample was prepared by the solid-state reaction method at 600 °C in an evacuated borosilicate tube. X-ray diffractograms revealed the formation of two not superconducting minor impurity phases, Fe7Se8 and FeSe, both with hexagonal structures. Resistivity measurement showed that the onset superconducting temperature occurs at Tconset ~ 8.6 K. Magnetic measurements were performed at high temperature and showed that the FeSe0.88 compound presents a ferromagnetic–paramagnetic phase transition at ~ 875 K.
High-pressure high-temperature syntheses that involve volatile-bearing aqueous fluids are typically accomplished by enclosing the samples in gas-tight welded shut noble-metal capsules, from which the bulk volatile content must be extracted to be analyzed with mass spectroscopy, hence making the analysis non-replicable. Here we describe a novel non-destructive method that ensures the identification and the quantitative estimate of the volatiles directly in the sealed capsule, focusing on fluid H2O–CO2 mixtures equilibrated with graphite at conditions of geological interest (1 GPa, 800 °C). We used a high-energy (77 keV) synchrotron X-ray radiation combined with a cryostat to produce X-ray diffraction patterns and X-ray diffraction microtomographic cross-sections of the volatile-bearing samples down to –180 °C, thus encompassing the conditions at which crystalline phases-solid CO2 and clathrate (CO2 hydrate)-form. The uncertainty of the method is < 15 mol%, which reflects the difference between the volatile proportion estimated by both Rietveld refinement of the diffraction data and by image analysis of the microtomograms, and the reference value measured by quadrupole mass spectrometry. Therefore, our method can be reliably applied to the analysis of frozen H2O–CO2 mixtures and, moreover, has the potential to be extended to experimental fluids of geological interest containing other volatiles, such as CH4, SO2 and H2S.
The coexistence of superconductivity and topology holds the potential to realize exotic quantum states of matter. Here we report that superconductivity induced by high pressure in three thallium-based materials, covering the phase transition from a normal insulator (TlBiS2) to a topological insulator (TlBiSe2) through a Dirac semimetal (TlBiSeS). By increasing the pressure up to 60 GPa, we observe superconductivity phase diagrams with maximal Tc values at 6.0-8.1 K. Our density-functional theory calculations reveal topological surface states in superconductivity phases for all three compounds. Our study paves the path to explore topological superconductivity and topological phase transitions.
In this study, Ce0.95−xDyxCa0.02Bi0.03O2−δ (x = 0, 0.05, 0.10, 0.15, and 0.20) electrolyte powders were synthesized via the sol–gel method. Phase structure, surface chemical state and defect, micromorphology, direct band gap, thermal expansion, and electrical properties were characterized using X-ray diffraction (XRD), X-ray photoelectron and Raman spectroscopy, field emission scanning electron microscopy (FESEM), UV–Visible spectroscopy, thermal dilatometer, and AC impedance spectroscopy, respectively. XRD results confirmed formation of a single phase with cubic fluorite structure for all samples. XPS study and Raman spectroscopy analysis revealed the existence of oxygen vacancies in all the compositions. The estimated concentration of oxygen vacancies first increased and then decreased with the increase of Dy3+ doping content. The oxygen vacancy concentration was found to be highest for Ce0.85Dy0.1Ca0.02Bi0.03O1.915 composition among all the samples. FESEM analysis revealed a high density in the microstructure of all samples, and the average grain size of the sample x = 0.10 was larger than that of the other samples. UV–Vis spectroscopy showed the minimized direct band gap for Ce0.85Dy0.10Ca0.02Bi0.03O1.915. Impedance spectroscopy measurements revealed the highest total electrical conductivity and the lowest activation energy for the same composition Ce0.85Dy0.1Ca0.02Bi0.03O1.915, i.e., 3.53 × 10−2 S/cm at 700 °C and 0.79 eV, respectively. Linear thermal expansion results of all the samples showed moderate thermal expansion coefficients (TECs). Therefore, Ce0.85Dy0.1Ca0.02Bi0.03O1.915 is expected to be used as an electrolyte material for intermediate-temperature solid oxide fuel cells (IT-SOFCs).
Magnetic and structure transitions of Mn3–xFexO4 solid solutions under extreme conditions are clarified by neutron time-of-flight scattering diffraction and X-ray Mössbauer measurement. The ferrimagnetic-to-paramagnetic transition temperature (100 °C) of Mn2FeO4 spinel is different from the tetragonal-to-cubic structure transition temperature (180 °C). The structure transition temperature decreases with increasing pressure. The transition is not coupled with the magnetic transition. Synchrotron X-ray Mössbauer experiments have revealed the pressure effects on the distribution of Fe²⁺ and Fe³⁺ at the tetrahedral and octahedral sites in the spinel structure. Ferrimagnetic MnFe2O4 and Mn2FeO4 spinels show sextet spectral features with hyperfine structure elicited by internal magnetic fields. Cubic MnFe2O4 spinel and tetragonal Mn2FeO4 transform to high-pressure orthorhombic postspinel phase above pressures of 18.4 GPa and 14.0 GPa, respectively. The transition pressure decreases with increasing Mn content. The postspinel phase has a paramagnetic property. Mn2O10 dimers of two octahedra are linked via common edge in three dimentional direction. The occupancy of Fe²⁺ in the tatrahedral site is decreased with increasig pressure, indicating more oredered structure. Consequently, the inverse parameter of the spinel structure is increased with increasing pressure. The magnetic structure refinements clarify the paramagnetic and ferrimagnetic structure of MnFe2O4 and Mn2FeO4 spinel as a function of pressure. The magnetic moment is ordered between A and B sites with the anti-parallel distribution along the b axis. The nuclear tetragonal structure (aN, aN, cN) has the ferrimagnetic structure but the orthorhombic magnetic structure has the ferrimagnetic structure with the lattice constants (aM, bM, cM). The magnetic moment is ordered between A and B sites with the anti-parallel distribution along the bM axis.
A sharp focus of current research on superconducting superhydrides is to raise their critical temperature Tc at moderate pressures. Here, we report a discovery of giant enhancement of Tc in CeH9 obtained via random substitution of half Ce by La, leading to equal-atomic (La,Ce)H9 alloy stabilized by maximum configurational entropy, containing the LaH9 unit that is unstable in pure compound form. The synthesized (La,Ce)H9 alloy exhibits Tc of 148–178 K in the pressure range of 97–172 GPa, representing up to 80% enhancement of Tc compared to pure CeH9 and showcasing the highest Tc at sub-megabar pressure among the known superhydrides. This work demonstrates substitutional alloying as a highly effective enabling tool for substantially enhancing Tc via atypical compositional modulation inside suitably selected host crystal. This optimal substitutional alloying approach opens a promising avenue for synthesis of high-entropy multinary superhydrides that may exhibit further increased Tc at even lower pressures.
Tutton salts have been extensively explored in recent decades due to their attractive physical and chemical properties, which make them potential candidates for thermochemical heat storage systems and optical technologies. In this paper, a series of new mixed Tutton salts with the chemical formula (NH 4 ) 2 Mn 1–x Zn x (SO 4 ) 2 (H 2 O) 6 is reported. Crystals are successfully grown by the solvent slow evaporation method and characterized by powder X-ray diffraction (PXRD) with Rietveld refinement. In particular, the crystal structure of the mixed (NH 4 ) 2 Mn 0.5 Zn 0.5 (SO 4 ) 2 (H 2 O) 6 crystal is solved through PRXD data using the DICVOL06 algorithm for diffraction pattern indexing and the Le Bail method for lattice parameter and spatial group determination. The structure is refined using the Rietveld method implemented in TOPAS® and reported in the Cambridge Structural Database file number 2104098. Moreover, a computational study using Hirshfeld surface and crystal void analyses is conducted to identify and quantify the intermolecular interactions in the crystal structure as well as to determine the amount of free space in the unit cell. Furthermore, 2D-fingerprint plots are generated to evaluate the main intermolecular contacts that stabilize the crystal lattice. Density functional theory is employed to calculate the structural, thermodynamic, and electronic properties of the coordination [Zn(H 2 O) 6 ] ²⁺ and [Mn(H 2 O) 6 ] ²⁺ complexes present in the salts. Molecular orbitals, bond lengths, and the Jahn–Teller effect are also discussed. The findings suggest that in Mn-Zn salts several properties dependent on the electronic structure can be tuned up by modifying the chemical composition.
Ultraviolet-C light has significant application prospects in the fields of disinfection, air purification, etc. Herein, an effective UVC upconversion phosphor Y2SiO5:Pr3+ was successfully prepared, as evidenced by the XRD results. The diffuse reflection spectra of Y2SiO5: Pr3+ phosphors presented two distinct absorption bands corresponding to the electron transitions of 3H4 → 3P2 and 3H4 → 1D2, and the Eg was determined to be 4.22 eV for the Y2SiO5 host, which is very close to the Eg (4.172 eV) calculated by DFT. Under the excitation of 460 nm laser, two emission peaks centered at ~247 nm and ~ 258 nm were found in the range of 230-280 nm, which are attributed to the transitions of 4f5d → 3H4 and 4f5d → 3H5 of Pr3+ ions. With the help of temperature-dependent emission spectra, the phosphor demonstrated impressive thermal stability up to 150 °C. These findings indicate that the Y2SiO5: Pr3+ phosphor has the potential application in disinfection.
Due to environmentally friendly operation and on-site productivity, electrocatalytic singlet oxygen (¹O2) production via O2 gas is of immense interest in environment purification. However, the side-on configuration of O2 on the catalysts surface will lead to the formation of H2O, which seriously limits the selectivity and activity of ¹O2 production. Herein, we show a robust N-doped CuO (N–CuO) with Pauling-type (end-on) adsorption of O2 at the N–Cu–O3 sites for the selective generation of ¹O2 under direct-current electric field. We propose that Pauling-type configuration of O2 not only lowers the overall activation energy barrier, but also alters the reaction pathway to form ¹O2 instead of H2O, which is the key feature determining selectivity for the dissociation of Cu–O bonds rather than the O–O bonds. The proposed N dopant strategy is applicable to a series of transition metal oxides, providing a universal electrocatalysts design scheme for existing high-performance electrocatalytic ¹O2 production.
High pressure induces dramatic changes and novel phenomena in condensed volatiles1,2 that are usually not preserved after recovery from pressure vessels. Here we report a process that pressurizes volatiles into nanopores of type 1 glassy carbon precursors, converts glassy carbon into nanocrystalline diamond by heating and synthesizes free-standing nanostructured diamond capsules (NDCs) capable of permanently preserving volatiles at high pressures, even after release back to ambient conditions for various vacuum-based diagnostic probes including electron microscopy. As a demonstration, we perform a comprehensive study of a high-pressure argon sample preserved in NDCs. Synchrotron X-ray diffraction and high-resolution transmission electron microscopy show nanometre-sized argon crystals at around 22.0 gigapascals embedded in nanocrystalline diamond, energy-dispersive X‑ray spectroscopy provides quantitative compositional analysis and electron energy-loss spectroscopy details the chemical bonding nature of high-pressure argon. The preserved pressure of the argon sample inside NDCs can be tuned by controlling NDC synthesis pressure. To test the general applicability of the NDC process, we show that high-pressure neon can also be trapped in NDCs and that type 2 glassy carbon can be used as the precursor container material. Further experiments on other volatiles and carbon allotropes open the possibility of bringing high-pressure explorations on a par with mainstream condensed-matter investigations and applications. The nanostructured diamond capsule process with the inert gases solid argon and neon is demonstrated, where the trapped volatile gases could sustain their high-pressure states without confinement of conventional high-pressure vessels, opening up the possibility of in-depth investigations of high-pressure phenomena.
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