The high-pressure behaviour of the cubic phase of KPF6 - An X-ray single-crystal and entropy-maximization study

The high-pressure behaviour of cubic KPF6 up to 0.40 GPa was studied using single crystal-diffraction techniques. The crystal structures at ambient co nditions and at 0.15 GPa were investigated using maximum-entropy and Fourie r methods. Even under pressure the PF6 octahedra are highly disordered but the electron-density distribution differs from that at ambient conditons. T he cubic phase of KPF6 is highly compressible: The lattice parameter varies from a = 7.7813(3) Angstrom at normal pressure to a = 7.7144(5) Angstromat 0.40 GPa. Whereas powder samples already transform at about 0.1 to 0.2 GPa into the high-pressure phase KPF6II, the transition pressure for single cry stals is higher. The transition pressure depends not only on the crystal si ze but also on the crystal quality, and also time may play a role.