Phase transition anomalies of physical properties of pyroelectrics and improper ferroelectrics with charged point defects

Abstract

Abstract We propose a theoretical treatment of the charged point defect influence on anomalies of thermodynamic quantities, sound absorption coefficient, damping constant of the soft mode and intensities of elastic and inelastic light scattering at structural phase transitions in pyroelectrics and improper ferroelectrics. The role of point charges appears to be most important in the low-symmetry phase. In particular, if the screening is small enough the “critical index” of the sound attenuation coefficient increases and its frequency dependence changes. The elastic light scattering intensity may jump at the low-symmetry phase transition, where the magnitude and the magnitude of the step is estimated to be 103 times more than the Brillouin scattering intensity. In some cases the relative magnitude of the jump may appear to be rather small on the strong scattering background from charged defects taking place in the high-symmetry phase as well.