Coexistence of multiple morphotropic phase boundaries in strained La-doped BiFeO3 thin films

The coexistence of two phases across a morphotropic phase boundary (MPB), in piezoelectric materials, usually possess high electromechanical coupling response owing to the electrically controllable of transition between the two phases. Conventionally, morphotropic phase boundary is compositionally driven such as in PbZrO3–PbTiO3 system. Recent study has demonstrated it can be strain-induced in BiFeO3 as well. Using a combination of strain engineering in conjunction with chemical doping, we reveal the coexistence of multiple morphotropic phase boundaries (multi-MPBs) in highly strained BiFeO3 thin films through La doping. By applying an electric field, we show the reversible switching of these multi-MPBs. The discovery of these multi-MPBs in La-doped BiFeO3 thin films further enhance the electromechanical coupling response comparing with the previous observed MPB in pure BiFeO3, opening a new field to obtain high-performance piezoelectric materials.