Crystal structure and collective oxygen transport in high-temperature Ta$_{2}$O$_{5}$

Abstract

Ionic conduction in crystalline solids is conventionally understood to proceed via atomic-scale defects such as vacancies or interstitials. Here, by addressing the long-standing structural ambiguity of high-temperature tetragonal tantalum pentoxide (H-Ta$_2$O$_5$), we identify a qualitatively different transport mechanism. Based on first-principles calculations, we propose that H-Ta$_2$O$_5$ adopts a chiral framework composed of orthorhombic building units interconnected by screw-rotation planes, with a tantalum sublattice consistent with available transmission electron microscopy observations. Our ab initio molecular dynamics simulations reveal collective, one-dimensional oxygen migration within this stoichiometric lattice at temperatures of a few hundred degrees Celsius. This cooperative transport is enabled by the structural flexibility of octahedral coordination at the screw-rotation planes, which allows extensive lattice relaxation and dynamic charge redistribution, yielding a migration barrier of $\sim$0.2 eV. These results provide a microscopic interpretation of the reported high and anisotropic oxygen conductivity in H-Ta$_2$O$_5$.