Effect of NiO additive on microstructure,mechanical behavior and electrical properties of 0.2PZN–0.8PZT ceramics

A NiO-added Pb((Zn_1/3Nb_2/3)_0.20(Zr_0.50Ti_0.50)_0.80)O₃ system is prepared and investigated. The results reveal that Ni doping induces a phase transformation from the morphotropic phase boundary to the tetragonal phase side. Above the solubility limit of 0.3 wt% in NiO form, excess Ni ions segregate at the grain boundaries and triple junctions, which facilitate the formation of a liquid phase with excess PbO and lead to remarkable grain growth. The mechanical behavior (Vickers hardness (H_v) and fracture toughness (K_IC)) can be tailored by controlling the content of additive; this is accompanied by a transition in the fracture mode changed from transgranular without NiO additive to intergranular with 1.0 wt% NiO additive. Moreover, the NiO addition weakens the dielectric relaxor behavior and improves the piezoelectric properties simultaneously. The 0.2PZN–0.8PZT with 0.5 wt% NiO addition shows good transduction coefficient (d₃₃·g₃₃ = 10,050 × 10^?15 m²/N) and large fracture toughness (K_IC = 1.35 MPa m^1/2).