Poling engineering of (K,Na)NbO3-based lead-free piezoceramics with orthorhombic–tetragonal coexisting phases

Abstract

(K,Na)NbO₃ (KNN) is considered as one of the most promising candidates for lead-free piezoelectric ceramics, due to its large piezoelectric response as well as high Curie temperature. In the present study, the effect of various poling conditions on CaZrO₃-modified KNN-based lead-free piezoceramics was investigated. Featured by a polymorphic phase transition around ambient temperature, the samples differ from conventional Pb(Zr,Ti)O₃-based (PZT) ceramics in phase constitution, which inevitably influences the optimal poling conditions. It is found that the KNN ceramics can reach a saturated polarization state under reduced poling field and at short times, compared with PZT. Besides, poling at a relatively high temperature of 120 °C can yield an enhanced piezoelectric constant d₃₃ of up to 345 pC N⁻¹. The poling behavior of CaZrO₃-modified KNN-based ceramics is rationalized by the competition between domain reorientation and space charge accumulation.