On the application of a frustration model to the phase diagram of tetramethylammonium-chlorometallates and other A₂BX₄ compounds

Abstract

A semimicroscopic model for incommensurate crystal phases studied earlier is applied to three-dimensional systems occurring in nature. The structure and symmetry of the various phases are discussed and compared with experimental results. The model gives a unifying picture of a large family of compounds with β-K₂-SO₄ structure. The superspace group symmetry is shown to give a unification of the symmetry of the various incommensurate and commensurate phases.