[(Na0.5K0.5)(1-x)Li-x](Nb0.96Sb0.04)O-3 [NKLNS100x] ceramics with 0.0 <= x <= 0.1 were sintered at 1040 degrees 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 roperties of k(p) = 0.43, d(33) = 243 pC/N and epsilon(T)(33)/epsilon(0) = 990. The [(Na0.5K0.5)(0.95)Li-0.05](Nb0.96Sb0.04)O-3 [NKLNS5] ceramics sintered at 960 degrees C also showed a high density by the addition of CuO, due to the production of the CuO and Na2O-related liquid phase. The Cu2+ ions were considered to replace Nb5+ 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, epsilon(T)(33)/epsilon(0) = 600 and d(33) = 170 pC/N were obtained from the specimen containing 1.5 mol% of CuO sintered at 960 degrees C for 2 h. (C) 2010 Elsevier B.V. All rights reserved.