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 degrees C and sintered at 850-1100 degrees 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 degrees C lower and 50 degrees C higher, respectively than in NKN. With increasing addition of Cu to NKN and NKLN the remanent polarization (P-r) increased and coercive field (Er) decreased. NKLN prepared with 0.4 wt% CuO exhibited a saturation polarization (P-sat) of 30 mu C/cm(2), remanent polarization (P-r) of 27 mu C/cm(2) and coercive field (E-c) of 1.0 kV/mm. CuO caused the NKLN ceramics to harden considerably; the mechanical quality factor (Q(m)) increased from 50 to 260, d(33) similar to 285 and piezoelectric coupling factors were >0.4. (C) 2010 Elsevier Ltd. All rights reserved.