0000000000171945
AUTHOR
A. K. Tyagi
High-pressure study of ScVO4by Raman scattering andab initiocalculations
We report results of experimental and theoretical lattice-dynamics studies on scandium orthovanadate up to 35 GPa. Raman-active modes of the low-pressure zircon phase are measured up to 8.2 GPa, where the onset of an irreversible zircon-to-scheelite phase transition is detected. Raman-active modes in the scheelite structure are observed up to 16.5 GPa. Beyond 18.2 GPa we detected a gradual splitting of the ${E}_{g}$ modes of the scheelite phase, indicating the onset of a second phase transition. Raman symmetries, frequencies, and pressure coefficients in the three phases of ScVO${}_{4}$ are discussed in the light of ab initio lattice-dynamics calculations that support the experimental resul…
High pressure phase transitions in NdVO4
Raman-scattering measurements on NdVO4 suggest a pressure-induced zircon to monazite phase transition beyond 5.9 GPa. The monazite phase undergoes a second phase transition to a yet unknown phase at 18.1 GPa. Lattice-dynamics calculations well support the experimental findings and predict a possible orthorhombic structure for the post-monazite structure of NdVO4.
In situ high-pressure synchrotron X-ray diffraction study of the structural stability in NdVO4 and LaVO4
Abstract Room-temperature angle-dispersive X-ray diffraction measurements on zircon-type NdVO 4 and monazite-type LaVO 4 were performed in a diamond-anvil cell up to 12 GPa. In NdVO 4 , we found evidence for a non-reversible pressure-induced structural phase transition from zircon to a monazite-type structure at 6.5 GPa. Monazite-type LaVO 4 also exhibits a phase transition but at 8.6 GPa. In this case the transition is reversible and isomorphic. In both compounds the pressure induced transitions involve a large volume collapse. Finally, the equations of state and axial compressibilities for the low-pressure phases are also determined.
Corundum type indium oxide nanostructures: ambient pressure synthesis from InOOH, and optical and photocatalytic properties
A simple, cost effective, surfactant free and scalable synthesis of rhombohedral In2O3 (rh-In2O3) nanostructures with controllable size and shape has been developed under ambient pressure by thermal dehydration of InOOH nanostructures. The InOOH nanostructures have been prepared by solvothermal reaction between indium nitrate hydrate with tetramethylammonium hydroxide (TMAH) in anhydrous methanol at 140 °C without any surfactant. The structure and morphology of the nanostructures have been characterized in detail by X-ray powder diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM). The studies reveal that highly crystalline nanostructures of In…
Experimental evidence for pressure-driven isostructural and symmetry-breaking phase transitions on Bi14CrO24
Abstract We performed in situ X-ray diffraction experiments on Bi 14 CrO 24 under pressure up to 17.4 GPa. We discovered two reversible phase transitions that take place at 7.3 and 12.1 GPa. The first transition is isostructural and the second-transition involves a tetragonal-monoclinic symmetry reduction. Both transitions involve a small volume collapse indicating that they have a first-order character. For the three observed phases we determined a P – V equation of state. All of them are highly compressible having bulk moduli that range from 64 to 70 GPa. We also determined the axial compressibilities for difference phases, being the response of the structures to pressure anisotropic. Thi…
High-pressure lattice-dynamics of NdVO4
High-pressure Raman-scattering measurements and ab initio calculations on NdVO4 have been carried out up to 30 GPa. Our combined experimental and theoretical study confirms that beyond 5.9 GPa NdVO4 undergoes an irreversible zircon to monazite transition. The coexistence of zircon and monazite phases is experimentally observed up to ~8 GPa (which agrees with the theoretical transition pressure), stabilizing the monazite phase as a single phase around 10 GPa. Calculations additionally predict the existence of a second high-pressure phase transition at 12.4 GPa. This reversible phase transition has been experimentally observed beyond 18.1 GPa and remains stable up to 30 GPa. The post-monazite…