Mechanistic role of relaxor character in pressure-driven depolarization of lead-free BNT-based ferroelectrics

Bi0.5Na0.5TiO3(BNT)-based ferroelectric ceramics have emerged as promising candidates for high-power generator applications. However, the fundamental relationship between structure and pressure-induced depolarization behavior remains unclear. In this work, we systematically investigate the phase structure, domain configuration, phase transition behavior, and pressure-induced depolarization of 0.96(0.96(Bi0.5Na0.5)(Ti0.995Mn0.005)O3–0.04BiAlO3)–0.04NaNbO3 (abbreviated as 4NN) and 0.96(0.96(Bi0.5Na0.5)(Ti0.995Mn0.005)O3–0.04BiAlO3)–0.04KNbO3 (abbreviated as 4KN) composition ceramics. Both 4KN and 4NN exhibit similar phase structures featuring nanodomain configurations. However, 4NN demonstrates stronger relaxor character, with a higher degree of nanoregional ordering compared to 4KN. Under hydrostatic pressure (0–450 MPa), 4NN shows greater variations in ΔPmax, ΔPr, ΔEc, and Ploss than 4KN, indicating a more significant pressure-induced depolarization effect. Analysis of E–P phase diagrams and phase transition dynamics reveals that the well-ordered nanoregions of 4NN suppress phase transition relaxation, facilitating the ferroelectric–relaxor transition, and enhancing the depolarization-driven charge release. These findings elucidate the critical factors and underlying mechanisms governing pressure-induced depolarization in BNT-based materials, providing valuable insights for the rational design of high-performance lead-free ceramics for high-power pulsed applications.