Structural and thermal properties of H6Ta2O17

Abstract

The structural, electronic, mechanical, and thermal properties of H6Ta2O17 are studied using density functional theory. The Helmholtz free energy is computed for various symmetry constraints on the H6Ta2O17 structure during lattice structure optimization and atomic configuration relax- ation. The Helmholtz free energies calculated from Γ-point phonon frequencies demonstrate a pref- erence for slightly lowered symmetry, preferring triclinic symmetry rather than the experimentally determined orthorhombic symmetry. Elastic constants are obtained for the symmetry-enforced (i.e., orthorhombic) structure and are used to calculate the structure’s mechanical and thermal properties including its bulk, shear, and Young’s moduli, Poisson ratio, Pugh ratio, longitudinal and shear sound velocities, and Debye temperature. Using the Born criteria, the symmetry-enforced structure is shown to be mechanically stable. The electronic band structure for H6Ta2O17 is pre- sented and found to exhibit a large indirect band gap.