Ternary doping of Na+, Bi3+ and La3+ to improve piezoelectric constant and electrical resistivity simultaneously in calcium bismuth niobate ceramics

Abstract

High Curie-temperature layer-structured calcium bismuth niobate (CaBi2Nb2O9) piezoelectric ceramics are promising for important application in high-temperature vibration sensors. However, such application is currently limited due to not only poor high-temperature piezoelectric constant (d33), which is attributable to spontaneous polarization along a-b plane and high coercive fields, but also inferior high-temperature electrical resistivity, which results from volatilization of Bi2O3 during the sintering process that increases defect concentration of oxygen vacancies. Herein, we report a Na+, Bi3+ and La3+ ternary-doping-strategy to obtain Ca0.8(Na0.5La0.3Bi0.2)0.2Bi2Nb2O9 ceramics, which exhibited higher piezoelectric constant and larger electrical resistivity as accompanied by a better thermal stability at high-temperatures. The piezoelectric constant was enhanced from 8.8 pC/N in pristine CaBi2Nb2O9 to 13.4 pC/N in Ca0.8(Na0.5La0.3Bi0.2)0.2Bi2Nb2O9 ceramics, which is ascribed to the presence of pseudo-tetragonal structural distortion after La3+ doping. In addition, the electrical resistivity at 600 °C was increased by more than one-order of magnitude from 3.7 × 104 Ω cm in pristine CaBi2Nb2O9 to 1.4 × 106 Ω cm in Ca0.8(Na0.5La0.3Bi0.2)0.2Bi2Nb2O9 ceramics. Such significant improvement in electrical resistivity results from the reduction in oxygen vacancies due to ternary doping of Na+, Bi3+ and La3+ and stronger binding interaction between La3+ dopants and O2− in (Bi2O2)2+ layers in Ca0.8(Na0.5La0.3Bi0.2)0.2Bi2Nb2O9 ceramics. This work demonstrates an important way of employing chemical doping to improve piezoelectric constant and electrical resistivity simultaneously at high-temperatures to tune structural distortion in bismuth-layered structural CaBi2Nb2O9 ceramics.