Phase transitions and relaxer properties of doped quantum paraelectrics

Scaling properties of the paraelectric susceptibility with respect to temperature T and electric field E have been evidenced on solid solutions Sr1-xCaxTiO3, x much less than 1, and are explained within the framework of both the transverse Ising model (TIM) and an anharmonic oscillator model (AOM). The impurity-induced ferroelectric phase transitions occurring a x > x(c) approximate to 0.002 are modeled using a heterogeneous TIM, which is solved numerically. Alternatively, we present a coupled mode model involving a TIM and an AOM for the impurity and the host lattice subsystems, respectively. Relaxer properties such as dielectric poly dispersivity, quasi-first-order Raman scattering, bilinear coupling of optic and acoustic phonon modes and hyper-Rayleigh light scattering in the paraelectric regime are attributed to polar nanodomains due to fluctuations of defect-induced quenched random fields (RFs). Some of these features are modeled within the framework of the heterogeneous TIM including RF interactions. (C) 1999 Elsevier Science Ltd. All rights reserved.