Effect of CuO on the Sintering and Piezoelectric Properties of 0.95(Na 0.5 K 0.5 )NbO 3 –0.05SrTiO 3 Lead‐Free Piezoelectric Ceramics

CuO was used to enhance the sinterability of 0.95(Na 0.5 K 0.5 )NbO 3 –0.05SrTiO 3 (0.95NKN–0.05ST) ceramics. The poor sinterability of 0.95NKN–0.05ST ceramics was improved by the addition of 1.5 mol% CuO, so that they were well sintered even at 960°C with grain growth. The densification and grain growth were attributed to liquid‐phase sintering, probably due to the presence of a liquid phase containing SrO and CuO. The grain size decreased when the sintering temperature exceeded 960°C, due to the presence of a large amount of liquid phase. The microstructure of the 0.95NKN–0.05ST ceramics was considerably affected by even small variations of sintering temperature. The d 33 , k p , and Q m values increased with CuO addition due to the increased density and grain size. The high piezoelectric properties of k p =0.35, d 33 =200, and ɛ 33 T /ɛ o =1235 were obtained from the 0.95NKN–0.05ST ceramics containing 1.5 mol% CuO sintered at 960°C for 10 h.