Low-temperature sintering and piezoelectric properties of CuO-doped (K,Na)NbO3 ceramics

Abstract

The lead-free piezoelectric [(K0.485Na0.515)0.935Li0.065](Nb0.99Ta0.01)O3 (KNLNT) ceramics with a high mechanical quality factor (Qm) were prepared at low sintering temperature below 950°C for multilayered piezoelectric devices. Co-doping effect of 1mol% Na2CO3 and 0–1mol% CuO on the densification and piezoelectric properties were investigated. Co-doping effectively decreased the sintering temperature of KNLNT ceramics to 920°C. The co-doped KNLNT ceramics had a bimodal size distribution of large abnormal grains and small matrix grains above 900°C. When the sintering temperature increased above 900°C, a dielectric constant (εr) and loss (tan δ) decreased considerably and concurrently mechanical quality factor (Qm) greatly enhanced. The co-doped KNLNT ceramic with 1mol% Na2CO3 and 0.5mol% CuO had a high Qm and excellent piezoelectric properties when sintered at 940°C: a dielectric constant of 245 and loss (tan δ) of 0.0034, an electromechanical coupling factor (kp) of 0.449, and Qm of 904.