THE ROLE OF ORIENTATIONAL DISORDER IN THE PRESSURE-INDUCED AMORPHIZATION OF LITHIUM POTASSIUM-SULFATE

Raman scattering investigations of lithium potassium sulphate at high pressures have revealed that the sulphate tetrahedra are orientationally disordered in the high-pressure phases. In order to understand the nature of the disorder, the temperature dependence of the relative intensities of Raman lines associated with the sulphate internal modes are investigated. The results suggest a frozen-in static disorder rather than dynamic equilibrium between the occupancies of different orientations. The behaviour of the Raman linewidths up to a pressure of 250 kbar indicates successively broader distributions of the sulphate orientations. A mechanism of amorphization involving disorder in cation sublattices induced by the orientational disorder of sulphate is proposed.