Nonspherical Deformations of the Ions in Fluorite

Abstract

The structure amplitudes of CaF₂ measured by Togawa (J. Phys. Soc. Japan 19 (1964) 1969) are analyzed using methods developed by Kurki-Suonio (Ann. Acad. Sci. Fennicae A VI 93 (1962)). There is a considerable uncertainty in the scale and temperature parameters due to the residual term. The optimum values are slightly higher than those used by Togawa. The deviations of the ions from spherical symmetry are small but detectable. They can be characterized roughly by saying that the ions are slightly compressed by their nearest neighbours and extended towards the more empty regions, the fluorine ions also towards each other. The average trend of the experimental atomic factors coincides with the theoretical atomic factors within experimental errors.