Optimized energy-storage performance in Mn-doped Na_0.5Bi_0.5TiO₃-Sr_0.7Bi_0.2TiO₃ lead-free dielectric thin films

The 0.55Na_0.5Bi_0.5TiO₃-0.45Sr_0.7Bi_0.2TiO₃ (0.55NBT-0.45SBT) thin films with Mn doping were fabricated on the platinum-buffered Si substrates using the sol–gel technique. The impacts of Mn doping on the structure and properties of the thin films were systematically studied. Mn doping into the thin films can limit the valence transition of Ti cations to improve the insulation performance, and advance the ferroelectric properties. Ordered B-site cation displacement can be observed from the HADDF-STEM image, which can only be maintained in a single nano-sized crystal grain, and its order scale is limited by the grain size. The 0.55NBT-0.45SBT-0.01Mn film exhibited relatively high recoverable energy storage density (∼30.5 J/cm²) and efficiency (∼65%) at 2800 kV cm⁻¹. Frequency stability in a wide range (0.5 ∼ 20 kHz) and long-term antifatigue stability (1 × 10⁸ switching cycles) were also obtained, indicating their future applications in advanced dielectric capacitors for energy storage.