Piezoelectric and ferroelectric properties of Cu-doped K_0.5Na_0.5NbO₃lead-free ceramics

CuO-doped K0.5Na0.5NbO3(K0.5Na0.5NbO3+ x mol% CuO) lead-free ceramics have been prepared by an ordinary sintering technique. The results of x-ray diffraction patterns show that all the ceramics possess a pure pervoskite structure with orthorhombic symmetry. Based on the symmetry-conforming principle of point defects, defect dipoles are formed by the acceptor dopant ions Cu2+and O2-vacancies along the polarization direction and remain in the original orientation, providing a restoring force to reverse the switched polarization, which results in double polarization-electric hysteresis loops for the ceramics with x ≥ 0.50 at 100 Hz. That is, the ferroelectric dipoles are back to their original orientation on the removal of electric field due to the strong restoring force generated by defect dipoles. As a result, the ceramics (x ≥ 0.5) become considerably 'hardened' and possess an extraordinarily high Qm(825-2523) and simultaneously the other piezoelectric properties remain reasonably good (kp= 39%, kt= 47% and d33= 82 pC N-1).