Effect of Li 2 O on the defect polarization in CuO‐added (K 0.9 Na 0.1 )NbO 3 piezoelectric ceramics

CuO‐added (Li x K 0.9− x N a 0.1 )NbO 3 [C(L x K 0.9− x N 0.1 )N] ceramics with 0.0≤ x ≤0.05 were well‐sintered at 960°C for 6 hours. The lattice parameters of the specimens decreased with the addition of Li 2 O. Defect polarization ( P D ) formed between Cu 2+ 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 P D . When the P‐E curve was measured at temperatures higher than 75°C, the C(K 0.9 N 0.1 )N ceramic exhibited a normal P‐E hysteresis curve, whereas the C(L 0.04 K 0.86 N 0.1 )N ceramic maintained the double P‐E hysteresis curve up to 125°C, indicating that Li 2 O increased the thermal stability of P D . The latter specimen also showed the sprout shaped S‐E curve with a strain of 0.15% at 7.0 kV /mm after 10 4 cycles of a high electric field of 7.0 kV /mm.