Thermal Analysis and X-Ray Diffraction Study on LiKSO4: A New Phase Transition

Results of a detailed X-ray diffraction and thermal analysis study of the structural phase transitions in LiKSO4 carried out in the temperature range 123–1000 K are presented. The study indicates five phase transitions in the temperature range studied at 937, 707, 226 (268), 200 (251), and 186 (190) K (values in parentheses are for a warming process). The transition at 226 (268) K is reported for the first time. The different phases (from high to low temperature) show the space groups P63/mmc, P21cn, P63, P63mc, P31c, and Cmc21. The working conditions allowed us to obtain the different phases without twin crystals and without mixtures of several phases. We were thus able to determine the crystal structures of the different phases with more accuracy. The transitions at high temperature produce large variations in the crystal structure and the enthalpy of process is high, while at low temperature, as the structure is more compact, an activation energy is necessary, and the transitions show a thermal hysteresis, while the structural variation is as small as the enthalpy of the process.