Thermodynamic investigation on the PMN-PT stoichiometry change during thermocycling

A new thermodynamic investigation on the (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT, x = 0.25) single crystal has been carried out to understand the structural evolution during the thermocycling processes. The samples have been examined by three thermocycle regimes: 250-300 °C, 300-400 °C, and 400-600 °C, under air and argon atmospheres. The XRD refinement after thermocycling experiments identified the existence of rhombohedral phase (R3m), in addition to the retained cubic phase (Pm 3̅ m) at room temperature. It also predicted the existence of the retained rhombohedral phase at a high temperature. The results for the first time show that PMN-PT has a unique weight-change phenomenon during the thermocycling processes, i.e., weight loss is observed in the first stage while weight gain is observed in the last stage. It is believed that this novel phenomenon is affected by the structural evolution and the formation of the retained rhombohedral and cubic phases, respectively. It is believed that the stoichiometry changes observed are closely related to the electric fatigue phenomenon of piezo-electric materials.