A Model Calculation of Elastic Softening in Incommensurate-Ferroelastic Phase Transition of Some A₂BX₄-Type Crystals

Abstract

A model calculation of elastic softening in incommensurate-ferroelastic (commensurate) phase transition is presented. The adopted thermodynamic potential functional of the Landau-type is such as is applicable to some A₂BX₄-type crystals which have an incommensurate phase followed by a commensurate ferroelastic phase with the tripled unit cell. It has turned out that elastic softening so far reported in [N(CH₃)₄]₂CuCl₄ is well reproduced by the present model.