Structure Deformations and Existence of the α-β Transition in MXO 4 Quartz-like Materials

The paramount importance of M- X interactions in determining the existence or nonexistence of an α-β transition can be shown by a general survey of all known or predicted quartz-like materials, MX O 4. This distance, M- X, defined as the nonbonded radius sum, prescribes structure packing. If the M-O and X -O distances increase, interterahedron distortion will increase in relation to the decrease of the M-O- X angle, 0, and decrease of the tilt angle, δ. From a structural point of view, a borderline value of δ ∼ 22° or θ ∼ 136° has been extrapolated for the existence of an α-β transition.