Effects of BaZrO3 on the phase evolution and energy storage capacities of BNT-based lead-free dielectric ceramics

High-dielectric permittivity ceramics are widely used in electric circuits, especially capacitors. Recently, Pb-free dielectric ceramic materials have attracted extensive attention because of the toxicity of Pb-based ones. This study investigated the crystal structure and energy capacities of the ternary (1-x-y) (Bi_0.5Na_0.5)TiO₃ -y(Bi_0.5K_0.5)TiO₃ - xBaZrO₃ dielectric ceramics. The studied samples were synthesized using a conventional solid-state reaction method. A dense microstructure and a perovskite structure indicate that all samples are sintered well at 1150 °C. As a function of x and y, the rhombohedral-to-tetragonal phase transition happened in the ceramics, the lattice volume was increased, and the lattice parameter c/a ratio was decreased. The nonergodic relaxor samples, which showed the coexistence of rhombohedral-tetragonal phases, presented large total energy densities and energy loss densities. Besides, the ergodic relaxor samples, which showed a single tetragonal phase, presented large energy storage density and efficiency. At room temperature, the 18BZ4 sample showed the maximum energy storage density of 0.58 J/cm³ at 60 kV/cm, corresponding to the J_storage/E_max value of ∼9.7 × 10⁻³ J/(kV.cm²). In particular, the 18BZ4 sample presented an energy storage variation of ∼10 % in the temperature range of 25–125^oC. The results suggest a potential lead-free ceramic candidate for piezo-capacitor applications.