Excellent thermal stability of large polarization in (Bi_0.5Na_0.5)TiO₃-BaTiO₃ thin films induced by defect dipole

This work reports the large saturation polarization (P_m) of ~80 µC/cm² and remnant polarization (P_r) of ~60 µC/cm² in Mn-doped (Bi_0.5Na_0.5)TiO₃-BaTiO₃ (BNBTMn) thin films at elevated temperatures, which are substantially higher than the best values of the bulk counterparts, i.e. P_m (~40 µC/cm²) and P_r (~30 µC/cm²). The positive-up-negative-down (PUND) data suggested the contribution of switchable ferroelectric P_r is less than 50% in the overall P_r obtained in P-E loops at 300 K and keeps decreasing when heating. Thus, the observed large and thermally stable macroscopic polarizations in P-E loops is mainly attributed to the contribution of conformed local defect dipoles, namely Mn_Ti′-V_o ^•• (oxygen vacancy), under a strong electric field. The evolution of Raman spectra with temperature further confirm the presence of symmetry breaking associated with local polar in our BNBTMn thin films can be remained up to 750 K, much higher than previous reported Curie temperature. This work will shed light on the development of high-temperature nano-scale ferroelectric memories and other related devices with eco-friendly materials.