Improved Non-Piezoelectric Electric Properties Based on La Modulated Ferroelectric-Ergodic Relaxor Transition in (Bi_0.5Na_0.5)TiO₃-Ba(Ti, Zr)O₃ Ceramics

The characteristic transition from ferroelectric (FE) to ergodic relaxor (ER) state in (Bi_0.5Na_0.5)TiO₃ (BNT) based lead-free ceramics provides an efficient approach to bring a highly ordered phase back to a disordered one. It would be rational to utilize this transition to improve relevant non-piezoelectric properties based on domain decomposition. In this work, different La contents were introduced to 0.93(Bi_0.5Na_0.5)TiO₃-0.07Ba(Ti_0.945Zr_0.055)O₃ ceramics (BNT-BZT-xLa) to induce evolution of ergodic degree. The results reveal that with increasing La content, both the FE-ER transition temperature T_F-R and depolarization temperature T_d shift towards room temperature, implying a deepened ergodic degree. By modulation of ergodic degree, thermally stimulated depolarization current experiment shows a higher current density peak, and corresponding pyroelectric coefficient increases from 2.46 to 2.81 μC/(cm²∙°C) at T_d. For refrigeration, the indirect measurement demonstrates the ΔT maximum increases from 1.1 K to 1.4 K, indicating an enhanced electrocaloric effect. Moreover, the optimized energy storage effect is observed after La doping. With appearance of "slimmer" P-E loops, both calculated recoverable energy storage density W_rec and storage efficiency η increase to 0.23 J/cm³ and 22.8%, respectively. These results denote La doping conduces to the improvement of non-piezoelectric properties of BNT-based ceramics in a certain range. Therefore, La doping should be an adopted modification strategy for lead-free ceramics used in areas like refrigerator and pulse capacitors.