Phenomenological Theory of Phase Transition in Beta-Eucryptite

Abstract

A phenomenological theory of the commensurate (C)-incommensurate (IC) phase transition in beta-eucryptite is proposed, in which the free energy of the system is expanded in powers of the complex amplitudes of mass density wave for both IC and C phases and the coupling between both waves is assumed to be given by a product of the second order invariants constructed from the wave amplitudes. It is shown that, by choosing suitable parameters, our theory can predict the coexistence of IC and C phases in fairly wide temperature ranges as observed in the neutron scattering experiment.