High energy storage properties for the lead-free NBT-0.1BFO-0.068La relaxor ferroelectric film

Highlights: • Doping NBT-0.1BFO with La³⁺ enhances η to improve both U_re and η for NBT. • La³⁺ replacing Bi³⁺ makes the cations more disordered to increase relaxor behavior. • The NBT-0.1BFO-0.068La film shows a high U_re of 52.4 J/cm³. -- Abstract: For purpose of improving the energy storage properties for the Na_0.5Bi_0.5TiO₃ (NBT) film, NBT and BiFeO₃ (BFO) were formed into solid solution. The outcomes are that the recoverable energy density (U_re) has been greatly improved, but the energy storage efficiency (η) has decreased. In this study, doping the best ratio of 0.9Na_0.5Bi_0.5TiO₃-0.1BiFeO₃ (NBT-0.1BFO) solid solution film with La³⁺ is to improve η by enhancing the relaxor properties, so as to improve both U_re and η for the NBT film. A sol-gel process was used to prepare lead-free NBT-0.1BFO-xLa (x = 0.000, 0.023, 0.045, 0.068, 0.090) single-phase perovskite solid solution films. La³⁺ replaces Bi³⁺ to enhance the disorder degree of cations, which disrupts the ferroelectric long-range order in the original matrix and generates nano-scale polar regions (NPRs), giving rise to enhanced relaxor properties. This further reduces the remanent polarization (P_r), thereby improving η. Consequently, the NBT-0.1BFO-0.068La film exhibits a high U_re (52.4 J/cm³) and a considerable η (60.3%) under the electric field of 2700 kV/cm, and both U_re and η are improved compared with the NBT film. Moreover, the NBT-0.1BFO-0.068La film has high temperature stability ranging from −60 °C to 80 °C, indicating that it has potential application value for energy storage capacitors.