Study of Phase Transformation in BaTe2O6 by in Situ High-Pressure X-ray Diffraction, Raman Spectroscopy, and First-Principles Calculations.

Abstract

Structural and vibrational properties of orthorhombic BaTe2O6, a mixed valence tellurium compound, have been investigated by in situ synchrotron X-ray diffraction (XRD) studies up to 16 GPa and Raman spectroscopy up to 37 GPa using a diamond-anvil cell. The structure of orthorhombic BaTe2O6 has layers of [Te2O6]2–, formed by TeO6 octahedra and TeO5 square pyramids and Ba2+ ions stacked alternately along the ⟨010⟩ direction. A reversible pressure-induced structural transformation from the ambient orthorhombic (Cmcm) to a monoclinic (P21/m) structure is observed in both XRD and Raman spectroscopic investigations around 10 GPa. Ab initio calculations using density functional theory (DFT) corroborate this phase transition as well as the transition pressure. Both XRD and DFT calculations reveal that the high-pressure monoclinic structure is closely related to the ambient pressure orthorhombic structure, and the transformation is accompanied by a slight rearrangement of the structural units. Pressure evolution ...