Transformation of hardening to softening behaviors induced by Sb substitution in CuO-doped KNN-based piezoceramics

Abstract Pb-free piezoceramics of K0.5Na0.5Nb1-xSbxO3 + 1 mol% CuO are synthesized via a solid-state reaction. Furthermore, the transformation of hardening to softening behaviors induced by Sb substitution is exhibited and the corresponding microscopic mechanism is proposed. The CuO-doped K0.5Na0.5NbO3 ceramic without adding Sb exhibits extremely hardening characteristics (i.e., ultrahigh Qm of ∼2426, low tanδ of 0.32%, and pinched ferroelectric hysteresis loop) due to the formation of defect combinations ( ( Cu Nb ''' − V o • • ) ' and ( V o • • − Cu Nb ''' − V o • • ) • ). Whereas, the addition of Sb dramatically reduces the levels of defect combinations, leading to obviously softening properties (d33 > 210 pC N−1, kp > 40%, low Qm, and normal single P-E hysteresis loop). Our results indicate that the decrease of defect combinations with Sb addition should be responsible for the hardening-softening transformation of piezoelectricity and ferroelectricity in CuO-doped K0.5Na0.5Nb1-xSbxO3 piezoceramics.