Kinetics and symmetry changes in low-temperature phase transitions in LiKSO4

The kinetics and the symmetry changes associated with the low-temperature structural phase transitions in LiKSO4 have been investigated by single crystal neutron diffraction. The study indicated three clear phase transitions at 205 K (from sp. gr. P63 to sp. gr. P31c), at 189 K (to sp. gr. Cc) and 135 K in the cooling cycle; a phase change is also indicated at 165 K. All these transitions show thermal hysteresis. The full crystal does not undergo transformation at any of the transition temperatures but exhibits mixed phases. The kinetics of the phase transitions are characterised by prolonged equilibration times (days) which strongly depend on the thermal history of the sample. With the results of the structural investigations in the temperature range 300 K to 100 K, an attempt has been made to explain the anomalies and variant results observed in the physical properties of LiKSO4 at low temperatures.