High-Energy Storage Properties over a Broad Temperature Range in La-Modified BNT-Based Lead-Free Ceramics

The development of high-performance energy storage materials is decisive for meeting the miniaturization and integration requirements in advanced pulse power capacitors. In this study, we designed high-performance [(Bi_0.5Na_0.5)_0.94Ba_0.06]_(1-1.5x)La_xTiO₃ (BNT-BT-xLa) lead-free energy storage ceramics based on their phase diagram. A strategy combining phase adjustment and domain control via doping was proposed to enhance the energy storage performance. The obtained results showed that La³⁺ ions doped into BNT-BT improved the crystal structure symmetry and induced a strong dielectric relaxation behavior, which destroyed the long-term ferroelectric order and effectively promoted the formation of polar nanoregions. At x = 0.12, a high recoverable energy density (W_rec) of ∼5.93 J/cm³ and a relatively large energy storage efficiency (η) of 77.6% were obtained under a high breakdown electric field of 440 kV/cm. By using a two-step sintering approach for the microstructural optimization, the energy storage performance was further improved, yielding much higher W_rec (6.69 J/cm³) and η (87.0%). Additionally, both conventionally sintered and two-step-sintered samples showed excellent frequency stability (0.5-500 Hz), thermal endurance (25-180 °C), and fatigue resistance (10⁵ cycles). Regarding the pulse charge-discharge performance, the samples exhibited ultrashort discharge time (t_0.9 ∼ 89 ns for the conventionally sintered sample and ∼75 ns for the two-step-sintered sample) under an electric field of 240 kV/cm. Furthermore, the breakdown process of the material was simulated based on the finite element analysis, and it was shown that high breakdown strength of the material could be ascribed to fine grains, which significantly hindered the crack propagation during the application of the electric field. These results show that the presented materials have great potential as high-energy storage capacitors.