Effect of CuO on the Sintering Temperature and Piezoelectric Properties of (Na0.5K0.5)NbO3 Lead-Free Piezoelectric Ceramics

When a small amount of CuO was added to (Na0.5K0.5)NbO3 (NKN) ceramics sintered at 960°C for 2 h, a dense microstructure with increased grains was developed, probably due to liquid‐phase sintering. The Curie temperature slightly increased when CuO exceeded 1.5 mol%. The Cu2+ ion was considered to have replaced the Nb5+ ion and acted as a hardener, which increased the Ec and Qm values of the NKN ceramics. High piezoelectric properties of kp=0.37, Qm=844, and ɛ3T/ɛ0=229 were obtained from the specimen containing 1.5 mol% of CuO sintered at 960°C for 2 h.