In situ poling X-ray diffraction studies of lead-free BiFeO3–SrTiO3 ceramics
Zhilun Lu, Ge Wang, Linhao Li, Yuhe Huang, Antonio Feteira, Weichao Bao, Annette Kleppe, Fangfang Xu, Dawei Wang, Ian M. Reaney
Abstract
The origin of the large electrostrain in BiFeO 3 -BaTiO 3 (BF-BT) ceramics is controversial and has been attributed to either a field-induced transition to a long-range ferroelectric (FE) state or to multi-symmetry, polar nanoregions within a pseudocubic matrix whose vectors approximately align with the direction of the applied field. The (1- x )BiFeO 3 - x SrTiO 3 (BF- x ST) solid solution is structurally and microstructurally similar to BF-BT and provides a further case study to assess the origin of electrostrain. In BF- x ST, electrostrain is optimized at x = 0.4 (0.15%) which zero field, room temperature full-pattern X-ray diffraction (XRD) Rietveld refinement and scanning/transmission electron microscopy suggest is composed of 15% rhombohedral ( R ) cores, surrounded by 85% pseudocubic ( PC ) shells. In-situ poling synchrotron XRD reveals that all peaks remain singlet and exhibit no change in full width half maximum up to 100 kV cm −1 , confirming the absence of long-range FE order and the retention of short-range polar order, despite the large applied field. Strain anisotropy (calculated from individual peaks) of ε 220 > ε 111 > ε 200 and the associated strain orientation distribution however, indicate the existence of local orthorhombic ( O ), R and tetragonal ( T ) symmetries. The data therefore imply the existence under poling of multi-symmetry polar nanoregions in BF-0.4ST rather than a long FE phase, supporting the model described by Wang and co-workers (2019) for BF- BT compositions.