Defect engineering of high-performance potassium sodium niobate piezoelectric ceramics sintered in reducing atmosphere

Reducing atmosphere fired (K0.5Na0.5)NbO3-based ceramics open up an important opportunity for manufacturing lead-free multilayer piezoelectric devices cofiring with the base metal inner electrode. In this study, the effects of sintering atmosphere on the piezoelectric, dielectric, and insulating properties in Sn-doped (Na0.52K0.44Li0.04)NbO3 (KNN) were investigated. To establish the relationship between the defect structure and electrical properties, the thermally stimulated depolarization current (TSDC) technique was implemented. The electrical properties degrade severely when the pure KNN ceramics are sintered in reducing atmosphere, compared with the ceramics sintered in air. The reason is that the oxygen vacancy concentration in reduced fired ceramics is much higher than that in air fired ceramics. However, the 0.6 mol% Sn-doped KNN ceramics sintered in reducing atmosphere exhibit comparable electrical properties to the air fired ceramics. From the TSDC analysis, the reducing atmosphere fired ceramics have approximately the same oxygen vacancy concentration as the air fired ceramics because B-site substituted Sn works as an acceptor.