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

Among typical ferroelectric materials, Bi 0.5 Na 0.5 TiO 3 (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 ( P r ) 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 ( E b ) and slimming P – E loops, which typically leads to deteriorated ferroelectric properties (reduced P max ). To overcome the above problems, this study investigates (0.94– x )Bi 0.5 Na 0.5 TiO 3 -0.06BaTiO 3 - x MgZrO 3:1 mol % Mn (BNT-BT- x MZ: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 P max (76.81 μC/cm 2 ). Concurrently, the incorporation of MZ promotes cationic disorder, strengthening relaxor behavior. This results in nearly unchanged remnant polarization ( P r ) but significantly reduced coercive field ( E c ). Consequently, a large polarization difference (Δ P = 70.44 μC/cm 2 ) 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 ( W rec ) of 55.76 J/cm 3 and efficiency (η) of 79.46%. In contrast to previous unilateral approaches solely pursuing high E b, 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.