Phenomenological model for the phase-transition sequence in betaine calcium chloride dihydrate

Abstract

Betaine calcium chloride dihydrate exhibits a sequence of over eleven structurally modulated phases, as well as a reentrant incommensurate phase. This work shows that a phenomenological model based on a one-dimensional order parameter and involving a term of the form ${P}^{2}$(\ensuremath{\partial}P/\ensuremath{\partial}z${)}^{2}$ is adequate to account for this complex behavior.