Microstructure and piezoelectric properties of CuO added (K, Na, Li)NbO3 lead-free piezoelectric ceramics

Lead-free Na0.5K0.5NbO3 (NKN) and Na0.475K0.475Li0.05NbO3 (NKLN) ceramics doped with CuO were prepared by the mixed oxide route. The powders were calcined at 850–930 °C and sintered at 850–1100 °C. Small additions of CuO reduced the sintering temperature and increased the density to 96% theoretical. Cu first appears to enter the A site then the B site. In NKLN the orthorhombic–tetragonal and tetragonal–cubic phase transitions are approximately 150 °C lower and 50 °C higher, respectively than in NKN. With increasing addition of Cu to NKN and NKLN the remanent polarization (Pr) increased and coercive field (Ec) decreased. NKLN prepared with 0.4 wt% CuO exhibited a saturation polarization (Psat) of 30 μC/cm2, remanent polarization (Pr) of 27 μC/cm2 and coercive field (Ec) of 1.0 kV/mm. CuO caused the NKLN ceramics to harden considerably; the mechanical quality factor (Qm) increased from 50 to 260, d33 ∼ 285 and piezoelectric coupling factors were >0.4.