MgZrO₃-Doped BNT-Based Ferroelectric Thin Films Achieve Superior Energy Storage Performance through Synergistic Optimization of Polarization Intensity and <i>P</i>–<i>E</i> Hysteresis Loop Shape

Among typical ferroelectric materials, Bi0.5Na0.5TiO3 (BNT) has attracted significant research attention owing to its high intrinsic polarization and polymorphic phase transitions. However, the practical application of pure BNT in high-performance energy storage devices has been limited by its large remnant polarization (Pr) and broad P–E hysteresis loops. Previous studies on element-doped BNT-based materials for enhanced energy storage performance have primarily focused on improving dielectric breakdown strength (Eb) and slimming P–E loops, which typically leads to deteriorated ferroelectric properties (reduced Pmax). To overcome the above problems, this study investigates (0.94–x)Bi0.5Na0.5TiO3-0.06BaTiO3-xMgZrO3:1 mol % Mn (BNT-BT-xMZ:Mn, x = 0, 0.03, 0.06, 0.09, 0.12) thin films. MZ doping induces lattice expansion within the material, where larger domain sizes enhance polarization behavior, leading to increased Pmax (76.81 μC/cm2). Concurrently, the incorporation of MZ promotes cationic disorder, strengthening relaxor behavior. This results in nearly unchanged remnant polarization (Pr) but significantly reduced coercive field (Ec). Consequently, a large polarization difference (ΔP = 70.44 μC/cm2) and slim P–E hysteresis loops are achieved, and synergistic optimization of ferroelectric properties and relaxor characteristics enables the thin film to achieve superior energy storage performance under moderate electric fields (∼2250 kV/cm), ultimately achieving optimal comprehensive performance at x = 0.09, with a recoverable energy density (Wrec) of 55.76 J/cm3 and efficiency (η) of 79.46%. In contrast to previous unilateral approaches solely pursuing high Eb, the synergistic optimization strategy for polarization intensity and P–E hysteresis loop shape provides insights and design principles for modifying thin films as energy storage capacitors.