Effect of poling on dielectric anomalies at phase transitions for lead magnesium niobate-lead titanate crystals in the morphotropic phase boundary region

Abstract

Dielectric measurements are reported as a function of temperature for phase transformations in the lead magnesium niobate-lead titanate system (PMN-PT). Data are given for single crystal specimens in the morphotropic phase boundary (MPB) region. Transition temperatures were determined from dielectric loss data. The characteristics for both poled and unpoled crystals are compared. Values of dielectric constant were found to increase after poling at room temperature, and an anomaly was induced at the lower-temperature transition. Details are reported for these properties depending upon composition within the MPB region. At room temperature, the poled crystals had high values for dielectric constant (e.g., 5000–15 000), piezoelectric coefficient (e.g., 1000–4000pC∕N), and electromechanical coupling factor (e.g., >0.9). The temperature dependence of dielectric properties is treated in terms of competing phases at transformations, with a change from continuous to discontinuous behavior with increasing PT content towards the MPB. The effect of poling on the induction of the tetragonal (T) phase, with a lowering of the low temperature to tetragonal (LT→T) phase transformation temperature, is discussed. Piezoelectric crystals with the highest depoling temperature were farthest away from the MPB in the MPB region. This information should be useful for the application of PMN-PT piezoelectric crystals.