Uncovering the symmetry of the induced ferroelectric phase transformation in polycrystalline barium titanate

Microstructural design is a widespread approach to tailor the properties of functional materials with the size effect being an effective constraint that modifies physical phenomena. In this work, we investigate the grain size effect on the properties and the electric field induced phase transformation behavior in barium titanate. A broad range of unimodal average grain size distribution between 0.4 and 15 μm was successfully sintered avoiding abnormal grain growth. Samples with a grain size close to the range of 1–2 μm, balancing microstructural strain, presence, and mobility of domain walls to allow the field induced crystal phase transformation, showed optimal electromechanical and dielectric properties. By means of in situ high energy x-ray diffraction and a high-resolution multianalyzer detector, we distinguish and quantify a tetragonal–orthorhombic phase transformation induced by an electric field, providing unambiguous proof of this induced phase transformation. These results contribute to the understanding of fundamental questions about the piezoelectric effect in barium titanate and consequently other similar systems