Systematics of fluorite-related structures. I. General principles

The Kang-Eyring system of description of fluorite-related anion-deficient s tructures is extended to the wide range of fluorite-related structures with vacancies in both anion and cation sites. 22 different types of modules ar e characterized on the base of the concept of module equivalence and 280 di fferent module orientations are obtained from the symmetry considerations. Possible ways of linking of modules are considered. It is shown that for ge ometrical description of fluorite-related structures the following characte ristics may be used: matrix of transformation from fluorite-related sublatt ice to real lattice and an average parameter a(F) of fluorite sublattice.