Journal of Applied Crystallography

Volume 41, Part 3 (June 2008)

short communications

 

Structure of K₂TaF₇ at 993 K: the combined use of synchrotron powder data and solid-state DFT calculations

L. Smrcok, M. Brunelli, M. Boca and M. Kucharík

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 -K₂TaF₇ phase. 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 FK 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.

Keywords: K₂TaF₇; dipotassium tantalum heptafluoride; Rietveld refinement; powder diffraction; density functional theory.

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