The origin of the large electrostrain in BiFeO₃-BaTiO₃ (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)BiFeO₃-xSrTiO₃ (BF-xST) solid solution is structurally and microstructurally similar to BF-BT and provides a further case study to assess the origin of electrostrain. In BF-xST, 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 ε₂₂₀ > ε₁₁₁ > ε₂₀₀ 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.

BiFeO ₃ -BaTiO ₃（BF-BT）陶瓷中的大电应变的起源是有争议的，并且归因于电场诱导的到长距离铁电（FE）态的跃迁，或者归因于其中的多对称极性纳米区域一个伪三次矩阵，其向量与施加场的方向大致对齐。的（1- X）的BiFeO ₃ - X的SrTiO ₃（BF- X ST）固溶体在结构上和微观结构类似于BF-BT，并提供了进一步的案例研究，以评估电致伸缩的起源。在BF- x ST中，将电应变优化为x = 0.4（0.15％），其中零场，室温全模式X射线衍射（XRD）Rietveld细化和扫描/透射电子显微镜表明由15％的菱面体（R）核组成，被85％的伪立方（PC）包围贝壳。原位极化同步加速器XRD显示，即使在100 kV cm ^-1以下，所有峰仍保持单峰态，半峰全宽没有变化，这证实了尽管存在广阔的应用领域。的应变ε各向异性（从各个峰计算）₂₂₀  >ε ₁₁₁  >ε ₂₀₀然而，相关的应变取向分布表明存在局部正交的（O），R和四边形（T）对称性。因此，数据暗示在BF-0.4ST中存在多个对称极性纳米区域，而不是一个长的FE相，这支持了Wang和他的同事（2019）描述的BF- BT组成的模型。