Influence of sample thickness on polarization hysteresis and energy storage in lead-free Bi_0.5Na_0.5TiO₃-based relaxor ceramics

Lead-free ceramics with superior energy storage performance and high conversion efficiency are critical for advancing the electronics industry and academic research. Dielectric capacitors, essential in modern power systems, are prized for their rapid charge/discharge capabilities and high power density. Bi_0.5Na_0.5TiO₃-based materials offer a promising platform for energy storage applications. Strategies such as compositional and structural modifications, domain engineering, and microstructural optimization have been employed to enhance their energy storage capacity and efficiency. In this study, compositional tuning was achieved by substituting (Al_0.50Nb_0.50)4+ into the Bi_0.47Na_0.46La_0.01Ba_0.05TiO₃ ceramic matrix (Bi_0.47Na_0.46La_0.01Ba_0.05Ti_1-x(Al_0.5Nb_0.5)_xO₃). The ionic radius and valence state variations of Al3+, Nb5+, and Ti4+ enhanced local electric field fluctuations, resulting in relaxor behavior, broadened dielectric peaks, and slim ferroelectric hysteresis loops. This approach yielded high energy storage density (W_r) and efficiency (η), especially for x = 0.10. The effect of sample thickness on energy storage performance was also systematically investigated. The x = 0.10 ceramic achieved a W_r of 1.51 J/cm3 and η of 73.99 % at a thickness of 0.50 mm with a dielectric breakdown strength (DBS) of 90 kV/cm. Remarkably, reducing the thickness to 0.15 mm increased the DBS to 190 kV/cm, resulting in a Wᵣ of 3.64 J/cm3 and η of 66.13 %. Both Wᵣ and DBS more than doubled with the reduction in thickness from 0.50 mm to 0.15 mm. These findings highlight that reducing the sample thickness is an effective strategy for significantly improving DBS and enhancing the overall energy storage performance of the ceramics. Furthermore, this study demonstrates that areal energy density (J/cm2) offers a more insightful and practical metric than volumetric energy density (J/cm3) for assessing energy storage performance across different compositions in ceramic energy storage materials.