The Crystal Structure of KMnF₃ at 50 K

Abstract

The crystal structure of KMnF₃ at 50 K has been determined and refined by least squares method. The crystals are tetragonal with space group P4⁄mbm and cell dimensions: a_t=5.894 and c_t=8.348Å (Z=4). Intensity data were collected from Weissenberg photographs by using a microphotometer. Refinement on 122 superlattice reflections reached R=0.17. The structure is a slight distortion of the perovskite structure in which the tilting of MnF₆ octahedra, around the [001]_t axis, is observed only on the alternate (001)_t planes. The structure is described in terms of successive condensation of the R₂₅ and M₃ soft phonon modes.