The existence of high-low inversion point of kalsilite.

Abstract

Kalsilite shows the domain structure corresponding with 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 revealed that the XRD 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) A. 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. -T.Y.