Evolution of crystallographic grain orientation and anisotropic properties of (K0.5Na0.5)NbO3 ceramics using BaTiO3 templates by reactive templated grain growth

Abstract

Platelike BaTiO3 (BT) templates were used for the first time to fabricate (001) textured K0.5Na0.5NbO3 (KNN) piezoelectric ceramics. Plakelike BT templates with a thickness of 1–1.5μm and a mean diameter of 10–15μm were synthesized by the topochemical microcrystal conversion method using Bi4Ti3O12 as precursor particles. A systematic investigation was conducted on illustrating the texture development and microstructure evolution as a function of heat-treatment conditions. It was found that the KNN–BT solid solution was formed between BT templates and matrix materials. The increase of sintering temperature and time induced an orthorhombic–tetragonal phase transition. And it was indicated that the dominant mechanism of texture development could be the abnormal grain growth in the textured KNN ceramics. A (001) orientation degree of 80% was achieved at 1130°C for 24h. The textured ceramics showed anisotropic electrical properties in the direction of parallel and perpendicular to the casting plane. The orthorhombic–tetragonal polymorphic phase transition To–t, the tetragonal–cubic ferroelectric phase transition TC, the dielectric constant εr and the remnant polarization Pr values for the perpendicular cut specimens were lower than the parallel cuts. The excellent electric properties at the parallel cuts were found to be the dielectric constant εr=810, the piezoelectric charge constant d33=163pC/N, and the electromechanical coupling factor kp=0.37.