Structure and electrical properties of lead-free Bi_0.5Na_0.5TiO₃-based ceramics for energy-storage applications

A new energy-storage ceramic system based on (1 - x)(Bi_0.5Na_0.5TiO₃-BaTiO₃)-xNaTaO₃ ((1 - x)(BNT-BT)-xNT) is reported in this study. XRD refinement indicated a composition induced rhombohedral to tetragonal phase transition. All the samples exhibited a dense microstructure with an average grain size of 1.2-1.9 μm. The introduction of NT greatly improved the temperature stability of the dielectric properties for the BNT-BT system. For compositions x = 0.03-0.15, the working temperature range spanned over 260 °C satisfying TCC_{150 °C} ≤ ±15%. The electric conductivity as a function of frequency followed the double power law. In the temperature region of 325-500 °C, the activation energy of DC conduction ranged from 1.47 eV to 1.71 eV, indicating intrinsic band-type electronic conduction. The optimum energy-storage properties were obtained in 0.90(BNT-BT)-0.10NT with an energy-storage density of 1.2 J cm^-3 and energy-storage efficiency of 74.8% at 10 kV mm^-1. The results demonstrate that (1-x)(BNT-BT)-xNT ceramics are promising candidates for high-temperature energy-storage applications.