Phase transitions in potassium, rubidium and thallium titanyl-orthophosphates: Brillouin and Raman studies

Abstract

In TTP and RTP, the Brillouin spectra around the ferroelectric-paraelectric transition are consistent with a Landau model for a second order transition, taking the appropriate couplings of the order parameter to the strains. In RTP a cental peak is observed, apparently connected with the freezing of the soft mode. A detailed Raman study of this soft mode shows a pronounced increase of its dielecmc polarization above 600 K, probably related to changes in the ionic conductivity, giving rise to significant intensity variations originating from electro-optic effects.