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

Abstract The lead-free piezoelectric [(K 0.485 Na 0.515 ) 0.935 Li 0.065 ](Nb 0.99 Ta 0.01 )O 3 (KNLNT) ceramics with a high mechanical quality factor (Q m ) were prepared at low sintering temperature below 950 °C for multilayered piezoelectric devices. Co-doping effect of 1 mol% Na 2 CO 3 and 0–1 mol% 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 (e r ) and loss (tan δ) decreased considerably and concurrently mechanical quality factor (Q m ) greatly enhanced. The co-doped KNLNT ceramic with 1 mol% Na 2 CO 3 and 0.5 mol% CuO had a high Q m 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 ( k p ) of 0.449, and Q m of 904.