Phases and phase transitions of KPF6

Potassium hexafluorophosphate KPF6 has been investigated by X-ray powder diffraction, calorimetry and Brillouin spectroscopy. With decreasing temperature, the crystal shows a sequence of phases: NaCl-type cubic-monoclinic-monoclinic with two-phase coexistence regions in between. In the cubic phase the elastic constants have been determined. c44 and c12 show a slight softening