Influence of thickness on dielectric energy storage of sol–gel prepared flexible BZT–NBT films on mica

As emerging sectors like new energy and flexible electronics increasingly require high-performance flexible energy storage devices, the development of lead-free inorganic dielectric films that exhibit superior energy storage capabilities and mechanical flexibility has emerged as a key area of research. In the present study, lead-free 0.94 BaZr_0.2Ti_0.8O₃–0.06 Na_0.5Bi_0.5TiO₃ (BZT–NBT) dielectric energy storage films were successfully prepared on flexible fluorophlogopite (Mica) substrates using a sol–gel. A systematic examination was conducted on how film thickness (80, 110, 150, and 200 nm) influences microstructure, electrical characteristics, and energy storage capabilities. Among all the specimens, the 110 nm-thick film exhibits the best overall performance: it has a high breakdown strength (E_b) of 2157 kV cm⁻¹, a maximum recoverable energy storage density (W_rec) of 8.38 J cm⁻³, and an energy storage efficiency (η) of 96.61%. Moreover, this film shows remarkable stability under harsh conditions: thermal stability (25–200 °C) with variation rates of 5.15% for W_rec and 6.08% for η, fatigue resistance (10⁷ cycles) with variation rates of 2.11% for W_rec and 2.24% for η, and bending durability (10⁴ cycles) with variation rates of 4.84% for W_rec and 5.70% for η.