In situ poling X-ray diffraction studies of lead-free BiFeO3–SrTiO3 ceramics

The origin of the large electrostrain in BiFeO3-BaTiO3 (BF-BT) ceramics is controversial and has been attributed to either a field-induced transition long-range ferroelectric (FE) state or multi-symmetry, polar nanoregions within pseudocubic matrix whose vectors approximately align with direction applied field. (1-x)BiFeO3-xSrTiO3 (BF-xST) solid solution structurally microstructurally similar BF-BT provides further case study assess electrostrain. In BF-xST, optimized at x = 0.4 (0.15%) which zero field, room temperature full-pattern X-ray diffraction (XRD) Rietveld refinement scanning/transmission electron microscopy suggest composed 15% rhombohedral (R) cores, surrounded by 85% (PC) shells. In-situ poling synchrotron XRD reveals that all peaks remain singlet exhibit no change full width half maximum up 100 kV cm−1, confirming absence FE order retention short-range order, despite Strain anisotropy (calculated from individual peaks) e220 > e111 e200 associated strain orientation distribution however, indicate existence local orthorhombic (O), R tetragonal (T) symmetries. data therefore imply under multi-symmetry BF-0.4ST rather than long phase, supporting model described Wang co-workers (2019) for compositions.