Thermodynamics of Stress and Electric Field Induced Phase Transition in Relaxor Ferroelectric Crystals

A thermodynamics based analysis of measured material behavior in (110) orientated (PMN-32%PT) and (PZN-4.5%PT) crystals under combined stress, electric field and temperature loading leads to a determination of the relative energy levels of phases. The approach is to perform path integrals to determine external work done by electrical and mechanical loads at constant temperature and to remove the effect of heat generated by irreversible strain and electric displacement increments. This yields relative internal energy density levels of phases. It also yields Gibbs energy density, a measure of the driving force for the phase transformation. The approach is used to analyze two types of phase transition, a jump type transition from rhombohedral to orthorhombic with associated hysteresis in (011) loaded PZN-4.5%PT, and a continuous transition from rhombohedral to orthorhombic with rotation through an intermediate monoclinic phase in (001)loaded PMN-32%PT.