Effect of Li2O and CuO additives on the structural and piezoelectric properties of (Na0.5K0.5)(Nb0.96Sb0.04)O3 lead-free piezoelectric ceramics

[(Na 0.5 K 0.5 ) 1− x Li x ](Nb 0.96 Sb 0.04 )O 3 [NKLNS100 x ] ceramics with 0.0 ≤ x ≤ 0.1 were sintered at 1040 °C for 2 h and the specimens with x ≥ 0.05 had a dense microstructure due to liquid phase sintering. The specimen with x = 0.05 had both orthorhombic and tetragonal phases, and showed good piezoelectric properties of k p = 0.43, d 33 = 243 pC/N and ɛ 33 T / ɛ 0 = 990. The [(Na 0.5 K 0.5 ) 0.95 Li 0.05 ](Nb 0.96 Sb 0.04 )O 3 [NKLNS5] ceramics sintered at 960 °C also showed a high density by the addition of CuO, due to the production of the CuO and Na 2 O-related liquid phase. The Cu 2+ ions were considered to replace Nb 5+ ions and act as a hardener, which increased the Q m value of the NKLNS5 ceramics. High piezoelectric properties of k p = 0.37, Q m = 560, ɛ 33 T / ɛ 0 = 600 and d 33 = 170 pC/N were obtained from the specimen containing 1.5 mol% of CuO sintered at 960 °C for 2 h.