Effects of rare-earth dopants on phase structure and electrical properties of lead-free bismuth sodium titanate-based ceramics

Abstract

In this work, the effects of rare earth (RE) dopants on the phase structure, microstructure, and electrical properties of lead-free bismuth sodium titanate (BNT)-based ceramics were studied. Rare earth elements (i.e., Sm, Gd, Ho, Pr, Y, and Yb) were selected as the dopants to replace the Bi site of Bi0.5(Na0.8K0.2)0.5TiO3 ceramics. It was found that the addition of moderate RE ions reduced the temperature of ferroelectric-relaxor transition (Tf-r) and the dielectric maximum at lower temperature, while the slight influence on the dielectric maximum at higher temperature and microstructure were observed. Hereby, the three-stage evolution of phase structure after introducing RE ions was confirmed. A high piezoelectric coefficient d33 of ∼190 pC/N was achieved due to the improved dielectric constant in the state with stable electric field-induced ferroelectric phase. The high strain property and converse piezoelectric coefficient d33∗ of ∼340 pm/V were obtained in the state with the coexistence of nonergodic and ergodic relaxor phases when Tf-r approached room temperature. The degenerated overall electromechanical properties exhibited in the state with complete ergodic relaxor phase. This study affords a significant guidance for optimizing the piezoelectricity of BNT-based ceramics utilizing rare earth dopants.