Structural Distortion in Perovskite Type KCaH3–xFx (0.54 ≤ x ≤ 3)

Abstract

Representatives of the solid solution series KCaH3–xFx were synthesized by solid state reactions from binary metal hydrides and fluorides. Crystal structures were analyzed by Rietveld refinement based on X‐ray powder diffraction. The degree of substitution was determined by refinement of site occupancy factors as well as elemental analysis for hydrogen. Three sections of x in KCaH3–xFx can be distinguished. For x < 0.54 no hydride fluoride exists, i.e. there is no hydride of the composition KCaH3 and the solid solution starts only at x = 0.54. The tetragonal SrTiO3 type structure with partial ordering of hydrogen and fluorine atoms is found for 0.54 ≤ x ≤ 1.7. Both anion positions show mixed occupation with some preference of hydrogen atoms for 8h and fluorine atoms for 4a sites (I4/mcm, SrTiO3 type). For fluorine‐rich compounds a solid solution with orthorhombic GdFeO3 type structure (Pnma) and a perfectly statistical distribution of hydrogen and fluorine atoms is found (1.8 ≤ x ≤ 3). Interatomic distances resulting from the structure refinements are in the range of typical K–H, K–F, Ca–H, and Ca–F distances for mainly ionic compounds.