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

Abstract

Pb-free piezoceramics of K 0.5 Na 0.5 Nb 1-x Sb x O 3 + 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 K 0.5 Na 0.5 NbO 3 ceramic without adding Sb exhibits extremely hardening characteristics (i.e., ultrahigh Q m 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 (d 33 > 210 pC N −1 , k p > 40%, low Q m , 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 K 0.5 Na 0.5 Nb 1-x Sb x O 3 piezoceramics.