Giant electrostrain via field induced structural transformation in Sm doped BiFeO3-PbTiO3 ceramics revealed by in-situ synchronous X-ray diffraction

This study identifies the structural origin of giant electrostrain in samarium-doped bismuth ferrite lead titanate (0.55Bi1-xSmxFeO3–0.45PbTiO3) ceramics. A giant peak-to-peak electrostrain (∼0.5 % at 60 kV cm^–1) was obtained for compositions with x = 0.20 (20Sm) during initial poling, superior to Pb(Zr,Ti)O3 based ceramics with similar phase transition temperature of 275 °C, coupled with a piezoelectric coefficient of 276 pC/N comparable with hard PZT. While 20Sm is a macroscopically pseudo-cubic relaxor in its unpoled state, an irreversible, field-induced transformation gives a tetragonal (c/a∼1.115) ferroelectric phase as revealed by in-situ poling synchrotron X-ray diffraction and confirmed by transmission electron microscopy. The field-induced domain structure of the tetragonal structure could be reversibly switched under AC field after transformation. Quantitative strain analysis confirmed that the structural transformation accounts for approximately half of the total electrostrain, with the remainder by domain switching. These results highlight the importance of field-induced structural transformations for the development of high-performance piezoelectrics.