Theoretical Investigation of Ferroelastic Phase Transition of Pure and Mixed Alkali Cyanide Systems by the Elastic Dipole Model. II. The Cubic–Monoclinic Phase Transition of Pure Rubidium Cyanide

Abstract

AbstractThe cubic–monoclinic structural phase transition of RbCN is investigated with the elastic dipole model. The calculation shows that the monoclinic structure of RbCN consists of two groups of dipoles of equal number but aligning in two different orientations, which are obtained from the strain of the unit cell in agreement with the experiments. A stable configuration of the two groups of dipoles is proposed. The alternate displacement of the cations calculated from this configuration agrees with the experiment in direction but is too large in magnitude due to the elastic continuum model used. The interaction between neighboring dipoles is the main part of the ordering energy in contrast to the ferroelastic case of KCN. In fact a new kind of ordering transition – antiferroelastic phase transition – is proposed for RbCN.