Local disorder in Na_0.5Bi_0.5TiO₃-piezoceramic determined by 3D electron diffuse scattering

Local structural distortions in Na_0.5Bi_0.5TiO₃-based solid solutions have been proved to play a crucial role in understanding and tuning their enhanced piezoelectric properties near the morphotropic phase boundary. In this work all local structural disorders in a lead-free ternary system, namely 85%Na_0.5Bi_0.5TiO₃-10%Bi_0.5K_0.5TiO₃-5%BaTiO₃, were mapped in reciprocal space by 3D electron diffraction. Furthermore, a comprehensive model of the local disorder was developed by analysing the intensity and morphology of the observed weak diffuse scattering. We found that the studied ceramics consists of plate-like in-phase oxygen octahedral nanoscale domains randomly distributed in an antiphase tilted matrix. In addition, A-site chemical short-range order of Na/Bi and polar displacements contribute to different kinds of diffuse scattering. The proposed model explains all the observed diffraction features and offers insight into the ongoing controversy over the nature of local structural distortions in Na_0.5Bi_0.5TiO₃-based solid solutions.