Structure of K2TaF7at 993 K: the combined use of synchrotron powder data and solid-state DFT calculations

Abstract

The structure of dipotassium tantalum heptafluoride, K2TaF7, was optimized by energy minimization in the solid state using a plane-waves DFT (density functional theory) computation for which the lattice parameters were obtained by the Le Bail technique from synchrotron X-ray powder diffraction data collected at 993 K. Owing to the sample's corrosiveness, it had to be loaded in a thin-walled Pt capillary. It was found that the structure corresponds to that of the β-K2TaF7phase. The Ta atoms in the TaF7−polyhedra are sevenfold coordinated by fluorine atoms positioned within 1.977–2.007 Å. The K atoms are surrounded by eleven (K1) or eight (K2) fluorine atoms. Every F atom in the structure is surrounded by three K atoms. The F...K contact distances vary from 2.57 to 3.32 Å. It is suggested that solid-state DFT methods may, in many cases, provide an alternative tool to standard Rietveld refinements for structure determination.