Relation between the anomalies of the elastic and dielectric characteristics of the Jahn-Teller DyVO4 crystal

The nature of the anomalies in the temperature behaviour of the dielectric susceptibility chi of the Jahn-Teller crystal DyVO4 is investigated and their relation to the anomalies in the elasticity modulus C is studied. This interrelationship is due to the fact that the distortion phase transition of the ferro-para type caused by the cooperative Jahn-Teller effect is also a transition of the antiferro-paraelectric type. The effect of an electric field on C and chi is studied. It is shown that in the field the crystal experiences a metaelectric transition of the antiferro-paraelectric type which is accompanied by a distortion ferro-antiferro transition. The microscopic parameters characterizing the contribution of various phonon modes to the intra- and inter-sublattice interaction are determined. It is shown that for certain values of the parameters in the crystal a ferridistortion polar phase is realized in a narrow temperature range at the boundaries at which the C and chi anomalies are particularly pronounced. The effect of an electric field on the elementary excitation spectrum is considered and on the basis of an analysis of the temperature dependence of the modes active in the phase transition a microscopic explanation of the elastic and dielectric anomalies is presented. It is shown that the phase transition is connected with complete (down to zero) softening of the quasi-acoustical mode accompanied by a partial softening of the quasi-optical branch which is transformed by the same representation as the spontaneous deformation of the crystal