Search results for "ICAD"
showing 10 items of 1297 documents
High-Pressure Raman Study of Fe(IO3)3: Soft-Mode Behavior Driven by Coordination Changes of Iodine Atoms
2020
[EN] We report high-pressure Raman spectroscopy studies of Fe(IO3)(3) up to nearly 21 GPa that have been interpreted with the help of density functional theory calculations, which include the calculation of phonon dispersion curves and elastic constants at different pressures. Zero-pressure Raman-active mode frequencies and their pressure dependences have been determined. Modes have been assigned and correlated to atomic movements with the help of calculations. Interestingly, in the high-frequency region, there are several modes that soften under compression. These modes have been identified as internal vibrations of the IO3 coordination polyhedron. Their unusual behavior is a consequence o…
Crystal Chemistry of CdIn2S4, MgIn2S4, and MnIn2S4 Thiospinels under High Pressure
2012
We report X-ray diffraction measurements in CdIn2S4, MgIn2S4, and MnIn2S4 thiospinels at room temperature and high pressures. The pressure dependences of the structural parameters have been determined and compared to those from theoretical calculations. It is found that the three thiospinels have similar bulk moduli (B-0) between 75 and 80 GPa (B-0' similar to 3). The degree of inversion of these thiospinels has also been determined. The three thiospinels undergo a phase transition toward a defect LiTiO2-type structure above 9.5, 8.3, and 6.8 GPa in CdIn2S4, MgIn2S4, and MnIn2S4, respectively. Interestingly, the low- and high-pressure phases belong to the same symmetry group (Fd-3m), the tr…
High-pressure polymorphs of TbVO4: A Raman and ab initio study
2013
Raman measurements on TbVO4 show the occurrence of three pressure-induced phase transitions. The first one, an irreversible transition from the zircon to the scheelite structure, occurs beyond 6.7 GPa. In addition, two reversible transformations take place at 26.7 and 34.4 GPa. The last transition was never reported before. The experimental findings are supported by structural and lattice-dynamics calculations that helped us to identify the post-scheelite phase as a monoclinic fergusonite structure. According to the calculations, the third transition involves a symmetry increase. An orthorhombic structure is proposed for the phase found above 34.4 GPa. The results have been compared with pr…
Structural and vibrational study of pseudocubic CdIn2Se4 under compression
2014
We report a comprehensive experimental and theoretical study of the structural and vibrational properties of a-CdIn2Se4 under compression. Angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy evidence that this ordered-vacancy compound with pseudocubic structure undergoes a phase transition (7 GPa) toward a disordered rocksalt structure as observed in many other ordered-vacancy compounds. The equation of state and the pressure dependence of the Raman-active modes of this semiconductor have been determined and compared both to ab initio total energy and lattice dynamics calculations and to related compounds. Interestingly, on decreasing pressure, at similar to 2 GPa, CdIn2Se…
Quasi-hydrostatic X-ray powder diffraction study of the low- and high-pressure phases of CaWO4 up to 28 GPa
2014
We have studied CaWO4 under compression using Ne as pressure-transmitting medium at room temperature by means of synchrotron X-ray powder diffraction. We have found that CaWO4 beyond 8.8 GPa transforms from its low-pressure tetragonal structure (scheelite) into a monoclinic structure (fergusonite). The high-pressure phase remains stable up to 28 GPa and the low-pressure phase is totally recovered after full decompression. The pressure dependence of the unit-cell parameters, as well as the pressure volume equation of state, has been determined for both phases. Compared with previous studies, we found in our quasi-hydrostatic experiments a different behavior for the unit-cell parameters of th…
Experimental and Theoretical Study of Bi2O2Se Under Compression
2018
[EN] We report a joint experimental and theoretical study of the structural, vibrational, elastic, optical, and electronic properties of the layered high-mobility semiconductor Bi2O2Se at high pressure. A good agreement between experiments and ab initio calculations is observed for the equation of state, the pressure coefficients of the Raman-active modes and the bandgap of the material. In particular, a detailed description of the vibrational properties is provided. Unlike other Sillen-type compounds which undergo a tetragonal to collapsed tetragonal pressure-induced phase transition at relatively low pressures, Bi2O2Se shows a remarkable structural stability up to 30 GPa; however, our res…
Complex high-pressure polymorphism of barium tungstate
2012
We have studied BaWO 4 under compression at room temperature by means of x-ray diffraction and Raman spectroscopy. When compressed with neon as a pressure-transmitting medium (quasihydrostatic conditions), we found that BaWO 4 transforms from its low-pressure tetragonal structure into a much denser monoclinic structure. This result confirms our previous theoretical prediction based on ab initio calculations that the scheelite to BaWO 4-II transition occurs at room temperature if kinetic barriers are suppressed by pressure. However, our experiment without any pressure- transmitting medium has resulted in a phase transition to a completely different structure, suggesting nonhydrostaticity may…
Synthesis of a novel zeolite through a pressure-induced reconstructive phase transition process
2013
et al.
Experimental and theoretical study of dense YBO3 and the influence of non-hydrostaticity.
2021
[EN] YBO3 is used in photonics applications as a host for red phosphors due to its desirable chemical stability, high quantum efficiency and luminescence intensity. Despite its fundamental thermodynamic nature, the isothermal bulk modulus of YBO3 has remained a contentious issue due to a lack of comprehensive experimental and theoretical data and its vibrational modes are far from being understood. Here, we present an experimental-theoretical structural and vibrational study of YBO3. From structural data obtained from synchrotron X-ray diffraction data and ab initio calculations, we have determined the YBO3 bulk modulus, isothermal compressibility tensor and pressure-volume (P-V) equation o…
Lattice dynamics study of nanocrystalline yttrium gallium garnet at high pressure
2014
This work reports an experimental and theoretical lattice dynamics study of nanocrystalline Y3Ga5O12 (YGG) garnet at high pressures. Raman scattering measurements in nanocrystalline Tm3+-doped YGG garnet performed up to 29 GPa have been compared to lattice dynamics ab initio calculations for bulk garnet carried out up to 89 GPa. Good agreement between the theoretical vibrational modes of bulk crystal and the experimental modes measured in the nanocrystals is found. The contribution of GaO4 tetrahedra and GaO6 octahedra to the different phonon modes of YGG is discussed on the basis of the calculated total and partial phonon density of states. Symmetries, frequencies, and pressure coefficient…