High-pressure X-ray diffraction study of SrMoO4 and pressure-induced structural changes (original) (raw)
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Pressure-induced volume collapse and structural phase transitions in SrRuO3
Journal of Solid State Chemistry, 2013
We report on the low temperature (6 K) structural properties of SrRuO 3 under quasi-hydrostatic pressure studied by synchrotron X-ray powder diffraction in a diamond anvil cell. First principle calculations predict a first-order perovskite (Pv) to post-perovskite (pPv) phase transition at ∼40 GPa accompanied by a 1.9% volume collapse. Our results rule out the occurrence of a pPv phase to 54 GPa. Instead, we find a Pv to monoclinic to triclinic sequence of phase transitions. The monoclinic to triclinic phase transition at ∼38 GPa is accompanied by a 3.5% volume collapse. X-ray absorption spectroscopy indicates that this volume collapse is not accompanied by a change in Ru valence state. Our results should help guide improvements to theoretical treatments of this and other correlated d-electron systems based on density functional theory.
Journal of Solid State Chemistry, 2008
The strontium chromium oxide [Sr 2 O 2 ][CrO 2 ] 1.85 misfit layer compound has been synthesised at highpressure and high-temperature conditions. Electron diffraction patterns and high-resolution transmission electron microscopy images along [001] show the misfit character of the different layers composing the structure with a supercell along the incommensurate parameter bE7b 1 E13b 2 . The modulated crystal structure has been refined within the superspace formalism against single-crystal X-ray diffraction data, employing the (3+1)-dimensional superspace group C 0 nmb(0s 2 0)0 0 s. The compound has a composite structure with lattice parameters a 1 ¼ 5.182(1) Å , b 1 ¼ 5.411(1) Å , c 1 ¼ 18.194(3) Å for the first, SrO, subsystem and the same a and c, but with b 2 ¼ 2.925(1) Å for the second, CrO 2 , subsystem. The layer stacking is similar to that of orthorhombic PbS(TiS 2 ) 1.18 , but with a much stronger intersubsytem bonding in the case of the oxide. The intersubsystem lattice mismatch is mainly handled by displacement modulations of the Sr atoms, correlated with modulations of the valence, the coordination and the anisotropic displacement parameters.
High pressure lattice dynamics, dielectric and thermodynamic properties of SrO
Physica B-condensed Matter, 2011
Using density functional theory and density functional perturbation theory we have studied the effects of hydrostatic pressure on lattice dynamics, dielectric and thermodynamic properties of the rocksalt (NaCl) and CsCl phases of SrO. The stability of the NiAs type structure, experimentally confirmed to be stable in BaO, is also investigated. Studying the lattice dynamics of the NaCl and CsCl phases at various pressures, in the range of the phase stability, we have found the lattice dynamical instabilities which govern the phase transitions between NaCl and CsCl phases with increasing and decreasing pressure. By monitoring the behaviour of the found soft modes, we have calculated the transition pressures upon compression and decompression of SrO crystal. Lattice dynamics calculations reveal that the rocksalt and CsCl structures are unstable with respect to the soft transversal acoustic modes at single points of the Brillouin zone, which points to the fact that the transitions are of displacive type. Responses to electric fields and thermodynamic properties at high pressures are also given and discussed. All our results are in a good agreement with experimental data where applicable.
Crystals
In this manuscript, we report the density functional theory-based first principles study of the structural and vibrational properties of technologically relevant M′ fergusonite (P2/c)-structured NdTaO4 and SmTaO4 under compression. For NdTaO4 and SmTaO4, ambient unit cell parameters, along with constituent polyhedral volume and bond lengths, have been compared with earlier reported parameters for EuTaO4 and GdTaO4 for a better understanding of the role of lanthanide radii on the primitive unit cell. For both the compounds, our calculations show the presence of first-order monoclinic to tetragonal phase transition accompanied by nearly a 1.3% volume collapse and an increase in oxygen coordination around the tantalum (Ta) cation from ambient six to eight at phase transition. A lower bulk modulus obtained in the high-pressure tetragonal phase when compared to the ambient monoclinic phase is indicative of the more compressible unit cell under pressure. Phonon modes are calculated for th...
Structural characterisation of the -type, high pressure phase of ruthenium dioxide
Journal of Physics and Chemistry of Solids, 1998
Cubic Pa%type RuOz was prepared from the ambient pressure, rutile-structured phase at 20 GPa and 1100°C in a multianvil device. The structure of this Pa3 phase was refiqed by time-of-flight, neutron powder diffraction on the quenched sample yielding a cell constant a = 4.85892(3) A and an oxygen positioaal parameter u = 0.35 Il5(8). The rutheniup cation is rhombohedrally coordinated with six anions at 1.9!93(4) A and two more distant anions at 2.9552(4) A. The minimum interpolyhedral O-O distance of 2.5045(5) A in this structude is the shortest known in any solid and is shorter than the intrapolyhedral O-O distances, which are of 2.6208(5) A. These short distances are the origin of the ve_ry low compressibility of this oxide phase, which approaches that of diamond. The Raman spectrum of Pa3-type Ru02 is consistent with group-theoretical calculations.
Journal of Synchrotron Radiation, 2008
The crystal and local atomic structure of monoclinic ReO 2 (-ReO 2 ) under hydrostatic pressure up to 1.2 GPa was investigated for the first time using both X-ray absorption spectroscopy and high-resolution synchrotron X-ray powder diffraction and a home-built B 4 C anvil pressure cell developed for this purpose. Extended X-ray absorption fine-structure (EXAFS) data analysis at pressures from ambient up to 1.2 GPa indicates that there are two distinct Re-Re distances and a distorted ReO 6 octahedron in the -ReO 2 structure. X-ray diffraction analysis at ambient pressure revealed an unambiguous solution for the crystal structure of the -phase, demonstrating a modulation of the Re-Re distances. The relatively small portion of the diffraction pattern accessed in the pressure-dependent measurements does not allow for a detailed study of the crystal structure of -ReO 2 under pressure. Nonetheless, a shift and reduction in the (011) Bragg peak intensity between 0.4 and 1.2 GPa is observed, with correlation to a decrease in Re-Re distance modulation, as confirmed by EXAFS analysis in the same pressure range. This behavior reveals that -ReO 2 is a possible inner pressure gauge for future experiments up to 1.2 GPa.
Influence of La doping on elastic and thermodynamic properties of SrMoO3
Journal of Alloys and Compounds, 2011
The elastic and thermodynamic properties for Sr1−xLaxMoO3 (x = 0.0, 0.05, 0.1, 0.15, and 0.2) with temperature have been investigated, probably for the first time, by using modified rigid ion model (MRIM). The computed results on the elastic constants (C11, C12, and C44) are the first report on them. Using these elastic constants we have computed other elastic properties such as B, β, G′, G, E, σ, B/G ratio, Cauchy pressure (C12 − C44) and Lame's parameters (μ, λ). We have also reported the thermodynamic properties such as ϕ, f, θD, θD1, υ0, υ1, γ, and α. The values of Young's modulus, shear modulus and compressibility for SrMoO3 are in good agreement with the available experimental data. The concentration (x) dependence of θD in Sr1−xLaxMoO3 suggests that increased La doping drives the system effectively away from the strong electron–phonon coupling regime. Specific heat is reported in the wide temperature range and compared with the respective experimental data available i...
High-pressure study of the Sr2CoWO6 ordered double perovskite tungstate oxide
Journal of Molecular Structure, 2008
Using synchrotron radiation and Raman spectroscopy and a diamond anvil cell we measured the pressure dependence of the lattice parameters and Raman modes of polycrystalline Sr 2 CoWO 6 . Angle-dispersive X-ray diffraction patterns were indexed and showed that at 2.2 GPa, the material transforms from the I4/m tetragonal structure to the P2 1 /n monoclinic structure. For pressure values between 2.2 and 12.7 GPa only monoclinic symmetries were found. We had difficulties with the convergence of the profile matching of the diffractogram taken at 12.7 GPa, indicating that the second phase-transition took place. To get more informations about these structural changes, an in-situ Raman spectroscopic study was conducted to explore the pressure-induced phase-transition sequence of Sr 2 CoWO 6 to pressures of 40.8 GPa at room-temperature. Group theory yields nine Raman-active modes for Sr 2 CoWO 6 (I4/m), all the predicted bands are observed at ambient conditions (phase I). The experimental results indicate that structural changes are observed at 2.15 and 11.15 GPa, which we attribute to phase transitions; thus, giving rise to two new phases, named as phase II and phase III, respectively. In the 9.33-14.84 GPa interval a coexistence of phases II and III is observed.
Pressure Induce Variations in the Lattice Constant and Energy Gap of SrThO3
JOURNAL OF NANOSCOPE (JN)
SrThO3 belong to stable perovskites family. Some theoretical works have been performed on this compound. However the pressure effect in the pressure range 0 to 30 GPa was never conducted. This work highlights the importance of the hydrostatic compression on the lattice constant and energy bandgap of the compound. Lattice parameter is found to decrease with increasing pressure. SrThO3 comes out as a direct band gap material. We discussed the effect of pressure on the energy band gap and got to know that overall energy band gap decreases as pressure increases. Finally we discussed the density of states of SrThO3 and plotted it against energy.
American Mineralogist, 2003
The crystal structure of synthetic kosmochlor, NaCrSi 2 O 6 , was studied using single crystal X-ray diffraction at high pressure. A four-pin diamond anvil cell, with 4:1 methanol:ethanol pressure medium, was used to achieve pressures to 9.28 GPa. Unit-cell data were collected at 20 pressures, and intensity data were collected at 13 of these pressures. Fitting the P-V data to a third-order Birch-Murnaghan equation yields V 0 = 418.84(3) Å 3 , K 0 = 134(1) GPa-1 , and K 0 ' = 2.0(3). Anisotropic compression was observed with unit strain axial ratios of 1:1.82:2.08. The CrO 6 octahedron has a bulk modulus K 0 = 90(16) GPa-1 , while the SiO 4 tetrahedron has K 0 = 313(55) GPa-1 , both with K 0 ' ∫ 4. An o-type rotation of the O3-O3-O3 linkage was observed with pressure, with-O3-O3-O3 decreasing from 172.8(2)∞ to 166.1(7)∞. Compression in kosmochlor is related to the stacking directions of distorted cubic closest packed O atom monolayers. Unit strain ellipsoids for diopside, hedenbergite, spodumene (C2/c and P2 1 /c), LiScSi 2 O 6 (C2/c and P2 1 /c), clinoenstatite, orthoenstatite, and Mg 1.54 Li .23 Sc .23 Si 2 O 6 (Pbcn and P2 1 cn) were generated and discussed in terms of closest packing systematics. A relationship between the anisotropy of compression of olivines and pyroxenes is established. A strategy to determine not only the direction of a stress field in deformed rocks, but also an estimate of the magnitude of stress is discussed in terms of comparing the anisotropy of olivine and pyroxene.