The existence of high-low inversion point of kalsilite

Abstract

Kalsilite shows the domain structure corresponding to the disordered oxygen atoms at two mirror equivalent sites. The domain structure was considered to be due to the high-low inversion, and the structural model of the high-form was constructed. The heating experiment was carried out, which revealed that the X-ray powder pattern changes at 1138 K. It was confirmed that kalsilite undergoes a displacive transformation like quartz and tridymite. The high-form is hexagonal, probably P6₃mc, with a=5.30(1), c=8.65(1)Å. The high-form was also considered to be divided into two groups, high-kalsilite (P6₃mc) and disordered high-kalsilite (P6₃⁄mmc). The Zellengleichen subgroup relations are found among these three polymorphs.