Microstructure-property relationships in liquid phase-sintered high-temperature bismuth scandium oxide-lead titanate piezoceramics

High-temperature piezoelectrics are necessary for aeronautic and aerospace applications. The principal challenge for the insertion of piezoelectric materials is their limitation for upper use temperature, which is due to low Curie temperature and increasing conductivity at high temperatures. We investigated processing, microstructure, and property relationships of (1-x)BiScO3-(x)PbTiO3 composition as a promising high-temperature piezoelectric. The effects of excess PbO and Bi2O3 and their partitioning in grain boundaries were studied using impedance spectroscopy, ferroelectric, and piezoelectric measurement techniques. Excess Pb addition increased the grain-boundary conduction and the grain-boundary area resulting in ceramics with higher AC-conductivity (tan delta = 0.9 and 1.7 for 0 and 5 at.% excess Pb at 350 degrees C and at 10 kHz) that were not resistive enough to pole. Excess Bi addition increased the resistivity (tan delta = 0.9 and 0.1 for 0 and 5 at.% excess Pb at 350 degrees C and at 10 kHz), improved poling, and increased the piezoelectric coefficient from 354 to 408 pC/N for 5 at.% excess Bi addition. Thus, excess Bi2O3 proved to be a successful liquid phase forming additive to improve the 0.37BiScO(3)-0.63PbTiO(3) piezoceramics for high-temperature applications, as a result of increased resistivity and enhanced piezoelectric activity.