CuO-added (LixK0.9-xNa0.1)NbO3 [C(LxK0.9-xN0.1)N] ceramics with 0.0 <= x <= 0.05 were well-sintered at 960 degrees C for 6 hours. The lattice parameters of the specimens decreased with the addition of Li2O. Defect polarization (PD) formed between Cu2+ ions and oxygen vacancies. Double polarization vs electric field (P-E) hysteresis and sprout-shaped strain vs electric field (S-E) curves were observed in these specimens with a large strain of 0.16% at 7.0 kV/mm, possibly owing to the presence of PD. When the P-E curve was measured at temperatures higher than 75 degrees C, the C(K0.9N0.1)N ceramic exhibited a normal P-E hysteresis curve, whereas the C(L0.04K0.86N0.1)N ceramic maintained the double P-E hysteresis curve up to 125 degrees C, indicating that Li2O increased the thermal stability of PD. The latter specimen also showed the sprout shaped S-E curve with a strain of 0.15% at 7.0 kV/mm after 104 cycles of a high electric field of 7.0 kV/mm.