Materials with the morphotropic phase boundary (MPB) exhibit an ultrahigh mechanical response to electrical inputs, which has been widely used in applications such as sensors and actuators. Recently, the rare-earth element doped $\mathrm{BiFe}{\mathrm{O}}_3$ (BFO) was found to possess a MPB between a rhombohedral polar phase and an orthorhombic antipolar phase with enhanced piezoelectric response, enabling it to be an attractive alternative to toxic Pb-based piezoelectric materials. Despite theoretical and experimental efforts, the phase transition behavior under electric fields has not been directly confirmed, leaving a gap in the understanding of the origin of enhanced piezoelectricity. Here, we have demonstrated an irreversible electric-field induced phase transition from the antipolar phase to the polar phase in Sm-doped BFO with the pre-MPB composition, and a reversible phase transition between the polar phase and the antipolar/nonpolar phase in Sm-doped BFO with the MPB composition. In situ transmission electron microscopy technique combined with thermodynamic calculation based on the Ginzburg-Landau-Devonshire theory indicates that the electric-field induced reversible phase transition leads to enhanced piezoelectric response and double P-E hysteresis loops. These results provide us a deep insight into the mechanism of exotic electromechanical response in the rare-earth element doped BFO system with the composition near the MPB.

• Received 20 January 2017
• Revised 27 April 2017

DOI:https://doi.org/10.1103/PhysRevB.95.214101