Temperature- and frequency-dependent dielectric response and energy-storage performance in high (100)-oriented Sc doped (Na0.85K0.15)0.5Bi0.5TiO3 films

Abstract

Highly (100)-oriented (Na_0.85K_0.15)_0.5Bi_0.5Ti_0.75Sc_0.25O₃ (NKBT-Sc) films with thicknesses ranging from about 460 to 860 nm were grown by utilizing TiO₂ layers engineering. Effects of TiO₂ layers on dielectric properties and energy-storage performances of NKBT-Sc films were investigated in a wide temperature range and a wide frequency range. The TiO₂ layers inserted alternately inside the NKBT-Sc films can enhance the (100) preferred degree of the film and it doesn't decrease with an increase in film thickness. Compared with NKBT-Sc films without TiO₂ layers, the TiO₂-coated NKBT-Sc films exhibit a great enhancement in electrical properties and energy-storage performance. The best dielectric properties with the largest dielectric constant (ε_r) of about 782 and the lowest dielectric loss (tan δ) of about 0.051 at 1 kHz, together with a maximum energy-density (W) of about 22.7 J cm⁻³ and corresponding efficiency (η) of about 51.5%, were obtained at room temperature in the 860 nm-thickness film with TiO₂ layers coated alternately with NKBT-Sc layers. Moreover, energy-density and the corresponding efficiency of the TiO₂-coated NKBT-Sc films varied slightly over a temperature range from −150 °C to 150 °C as well as at a frequency range from 100 Hz to 6 kHz, meaning a greatly enhanced temperature dependent energy-storage stability and a frequency dependent energy-storage stability. In addition, leakage current density (J) of the 860 nm-thickness TiO₂-coated NKBT-Sc film was maintained at a relatively low value. This also means that it can work in a wide operating temperature. This much enhanced energy-storage density and good temperature stability make NKBT-Sc films to be a promising lead-free material for energy storage capacitor applications.