Search results for "FINE"
showing 10 items of 1800 documents
High-pressure crystal structure, lattice vibrations, and band structure of BiSbO4
2016
The high-pressure crystal structure, lattice-vibrations HP crystal structure, lattice vibrations, and band , and electronic band structure of BiSbO4 were studied by ab initio simulations. We also performed Raman spectroscopy, infrared spectroscopy, and diffuse-reflectance measurements, as well as synchrotron powder X-ray diffraction. High-pressure X-ray diffraction measurements show that the crystal structure of BiSbO4 remains stable up to at least 70 GPa, unlike other known MTO4-type ternary oxides. These experiments also give information on the pressure dependence of the unit-cell parameters. Calculations properly describe the crystal structure of BiSbO4 and the changes induced by pressur…
Compressibility Systematics of Calcite-Type Borates: An Experimental and Theoretical Structural Study on ABO(3) (A = Al, Sc, Fe, and In)
2014
The structural properties of calcite-type orthoborates ABO(3) (A = Al, Fe, Sc, and In) have been investigated at high pressures up to 32 GPa. They were studied experimentally using synchrotron powder X-ray diffraction and theoretically by means of ab initio total-energy calculations. We found that the calcite-type structure remains stable up to the highest pressure explored in the four studied compounds. Experimental and calculated static geometries (unit-cell parameters and internal coordinates), bulk moduli, and their pressure derivatives are in good agreement. The compressibility along the c axis is roughly three times that along the a axis. Our data clearly indicate that the compressibi…
Effect of pressure on the structural properties and electronic band structure of GaSe
2007
The structural properties of GaSe have been investigated up to 38 GPa by monochromatic X-ray diffraction. The onset of the phase transition from the e-GaSe to a disordered NaCi-type structural motif is observed near 21 GPa. Using the experimentally determined lattice parameters of the layered e-phase as input, constrained ab-initio total energy calculations were performed in order to optimize the internal structural parameters at different pressures. The results obtained for the nearest-neighbor Ga-Se distance agree with those derived from recent EXAFS measurements. In addition, information is obtained on the changes of Ga-Ga and Se-Se bond lengths which were not accessible to a direct expe…
<title>In-situ x-ray absorption fine structure and x-ray diffraction studies of hydrogen intercalation in tungsten oxides</title>
1997
We present in-situ x-ray absorption fine structure (XAFS) (at the W L 3 -edge) and x-ray diffraction (XRD) studies of hydrogen intercalation into stable monoclinic (m-WO 3 ) and metastable hexagonal (h-WO 3 ) and cubic (c-WO 3 ) phases of tungsten oxide. The analysis of XAFS and XRD data allowed us to reconstruct the local environment around tungsten ions in the first coordination shell. The obtained results are compared with the existing structural models.
Fine tuning of thermoelectric performance in phase-separated half-Heusler compounds
2015
Two successful recipes to enhance the thermoelectric performance, namely carrier concentration optimization and reduction of thermal conductivity, have been combined and applied to the p-type (Ti/Zr/Hf)CoSb1−xSnx system. An intrinsic micrometer-scale phase separation increases the phonon scattering and reduces the lattice thermal conductivity. A substitution of 15% Sb by Sn optimizes the electronic properties. Starting from this, further improvement of the thermoelectric properties has been achieved by a fine tuning of the Ti to Hf ratio. The microstructuring of the samples was studied in detail with high-resolution synchrotron powder X-ray diffraction and element mapping electron microscop…
Atomistic simulations of the FeK-edge EXAFS in FeF3using molecular dynamics and reverse Monte Carlo methods
2016
Atomistic simulations of the experimental Fe K-edge extended x-ray absorption fine structure (EXAFS) of rhombohedral (space group ) FeF3 at T = 300 K were performed using classical molecular dynamics and reverse Monte Carlo (RMC) methods. The use of two complementary theoretical approaches allowed us to account accurately for thermal disorder effects in EXAFS and to validate the developed force-field model, which was constructed as a sum of two-body Buckingham-type (Fe–F and F–F), three-body harmonic (Fe–F–Fe) and Coulomb potentials. We found that the shape of the Fe K-edge EXAFS spectrum of FeF3 is a more sensitive probe for the determination of potential parameters than the values of stru…
Crossing the boundary between face-centred cubic and hexagonal close packed: the structure of nanosized cobalt is unraveled by a model accounting for…
2014
The properties of nanostructured cobalt in the fields of magnetic, catalytic and biomaterials depend critically on Co close packing. This paper reports a structural analysis of nanosized cobalt based on the whole X-ray diffraction (XRD) pattern simulation allowed by the Debye equation. The underlying structural model involves statistical sequences of cobalt layers and produces simulated XRD powder patterns bearing the concurrent signatures of hexagonal and cubic close packing (h.c.p. and f.c.c.). Shape, size distribution and distance distribution between pairs of atoms are also modelled. The simulation algorithm allows straightforward fitting to experimental data and hence the quantitative …
Discovery of new boron-rich chalcogenides: Orthorhombic B6X (X=S, Se)
2020
The authors thank T. Chauveau (LSPM) for help with Rietveld analysis, A. Jamali (LRCS) for assistance with SEM measurements, and Drs. Y. Tange (SPring-8) and N. Guignot (SOLEIL) for help in synchrotron experiments that were carried out during beamtimes allocated to proposals 2017A1047 & 2018A1121 at SPring-8 and proposal 20170092 at SOLEIL. Ab initio calculations have been performed using Rurik and Arkuda supercomputers. This work was financially supported by the European Union’s Horizon 2020 Research and Innovation Programme under Flintstone2020 project (grant agreement No. 689279). Z.W. thanks the National Science Foundation of China (grant No. 11604159). A.R.O. thanks the Russian Ministr…
Short and long range order of Half-Heusler phases in (Ti,Zr,Hf)CoSb thermoelectric compounds
2016
Abstract The structural properties of (Ti,Zr,Hf)CoSb thermoelectric Half-Heusler compounds were investigated by synchrotron radiation based techniques. The short-range order, in particular the environment of the Co atoms, was studied by extended X-Ray absorption fine structure spectroscopy and the long range order by powder X-Ray diffraction. Structural models were obtained for the single phase materials TiCoSb0.85Sn0.15, ZrCoSb0.85Sn0.15, and HfCoSb0.85Sn0.15. These models were transferred for the phase-separated material Ti0.5Hf0.5CoSb0.85Sn0.15. As a result, proving that each Half-Heusler phase was well ordered, apart from the intermixing of Ti and Hf on its designated crystallographic l…
New insight into δ-Pu alloy oxidation kinetics highlighted by using in-situ X-ray diffraction coupled with an original Rietveld refinement method
2018
Abstract The reactivity of a δ-Pu alloy was studied under dry oxygen at different temperatures. Phase analysis has shown the presence of α-and β-Pu2O3, PuO2, as well as the destabilisation of the δ-phase. The oxidation kinetics were studied using in-situ X-ray diffraction coupled with an original method of Rietveld refinement enabling an individual monitoring of the growth of each oxide. The results have evidenced a parabolic stage resulting from the thickening of the α-Pu2O3 layer, in which a compressive stress state develops. This stage is followed by the linear growth of a porous PuO2 scale.