The formation of (Zn,Ni)TiO3 secondary phase in NiO-modified Pb(Zn1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics

The formation of secondary phase in 4.0 mol.% NiO-added Pb(Zn1/3Nb2/3)O3-PbZrO3-PbTiO3 (PZN-PZT) ceramics, prepared by a conventional solid-state reaction method, was investigated. The results reveal that the segregated secondary phase in perovskite matrix was (Zn,Ni)TiO3 with hexagonal ilmenite structure, not the normally predicted NiO or ZnO. A new formation mechanism related to the enrichment of ZnO, NiO and TiO2 at grain boundaries has been proposed. Due to its non-ferroelectric structure, the occurrence of (Zn,Ni)TiO3 greatly deteriorates the piezoelectric properties.