High depolarization temperature and superior piezoelectric performance with complex structural evolution in BiFeO₃–PbTiO₃–(Sr_0.7Bi_0.2□_0.1)TiO₃ systems

Bismuth ferrite–based ferroelectric ceramics are considered strong competitors in high–temperature piezoelectric applications that benefits from their high depolarization temperature (T_d), but problems of large conductivity and low piezoelectric coefficient (d₃₃) should be tackled. BiFeO₃–PbTiO₃–x(Sr_0.7Bi_0.2□_0.1)TiO₃ (BF–PT–xSBT) ternary system are designed in this work that successfully resolves this tough paradox. Rietveld refinements show that this system exhibits multiphase coexistence with complex structural transition among rhombohedral, tetragonal and pseudocubic phase. Interestingly, a high T_d ~320 ℃ and d₃₃ ~ 236 pC/N are synergistically optimized in x=0.20 composition near pseudo–phase boundary, which are indicated by multi–scale techniques (phase structure, dielectric analysis etc.). What's more, dual electrostrain peaks appear at separate phase boundaries for x=0.20 and 0.66 compositions with distinct piezo/ferroelectric properties. Rayleigh law and piezoelectric force microscopy analysis clarify that the optimal electrostrain performance for both critical compositions are dominated by intrinsic (x=0.20) and extrinsic (x=0.66) contributions, respectively. This work not only provides a new BF–PT–xSBT system with a high T_d and superior d₃₃ that are promising candidates in high–temperature actuator and sensor applications, but also presents a possibility of multiphase–coexistence established exotic macroscopic performances.