STRUCTURE DEFORMATIONS AND EXISTENCE OF THE ALPHA-BETA TRANSITION IN MXO4 QUARTZ-LIKE MATERIALS

The paramount importance of M-X interactions in determining the existence or nonexistence of an alpha-beta transition can be shown by a general survey of all known or predicted quartz-like materials, MXO4. This distance, M-X, defined as the nonbonded radius sum, prescribes structure packing. If the M-O and X-O distances increase, intertetrahedron distortion will increase in relation to the decrease of the M-O-X angle, theta, and increase of the tilt angle, delta. From a structural point of view, a borderline value of delta approximately 22-degrees or theta approximately 136-degrees has been extrapolated for the existence of an alpha-beta transition. (C) 1994 Academic Press, Inc.