Structure and piezoelectric properties of Sm-doped BiFeO₃ ceramics near the morphotropic phase boundary

The evolution of crystal structure and piezoelectric properties of the Bi_1-xSm_xFeO₃ ceramics with compositions corresponding to the phase boundary region between the polar rhombohedral and anti-polar orthorhombic phases have been studied. The materials have been investigated using X-ray diffraction, transmission electron microscopy and piezoresponse force microscopy techniques. The diffraction measurements have allowed studying the crystal structure transformations depending on the dopant concentration and temperature. Similar to the compounds with x > 0.18, the lightly-doped samples have been found to adopt the non-polar orthorhombic structure at elevated temperatures. The research has clarified the correlation between the structural state and piezoelectric behavior. Substantial increase in piezoresponse observed for the phase-separated compounds having a dominant fraction of the rhombohedral phase has been discussed assuming significant extrinsic contribution associated with a metastable structural state changing under external electric field.