Innovative Design of BNKT-xSLZT Ceramics: Maximizing the Polarization Difference for Enhanced Energy Storage

Lead-free relaxor ferroelectric ceramics with outstanding energy-storage (ES) density (W_rec) and high ES efficiency (η) are crucial for advanced pulse-power capacitors. This study introduces a strategic approach to maximizing the polarization difference (ΔP) by inducing a transition from the ferroelectric phase to the ergodic relaxor (ER) phase. By employing this strategy, a series of ceramics, (1 - x)(Bi_0.5Na_0.4K_0.1)TiO₃-x(Sr_0.85La_0.1)(Zr_0.5Ti_0.5)O₃ (BNKT-xSLZT), with varying SLZT content (x = 0.05, 0.10, 0.15, and 0.20), were designed. The addition of SLZT enhances cationic disorder, induces vacancies at A sites, and disrupts long-range ferroelectric order, facilitating the formation of polar nanoregions and enhancing relaxor ferroelectric behavior. Furthermore, a viscous polymer process (VPP) technology is employed to optimize the ceramics' structure, aiming to increase the breakdown strength (E_b) and enhance ΔP. Ultimately, enhanced ES performance is demonstrated in BNKT-0.15SLZT_VPP, achieving a remarkable W_rec of 6.85 J/cm³ and η of 84% under 470 kV/cm. This composition demonstrates excellent stability with minimal variations in W_rec (3.0%) and η (4.4%) over the temperature range of 20-110 °C. Additionally, BNKT-0.15SLZT_VPP exhibits exceptional pulse charge-discharge properties, featuring a high discharge density of 3.72 J/cm³, a large power density of 164.2 MW/cm³, and a short discharge time (t_0.9) of 193 ns under 300 kV/cm. The study validates the practicality of BNKT-0.15SLZT_VPP for pulse capacitors and underscores the potential to enhance ES performance through A-site donor doping and VPP technology. This work provides a comprehensive understanding of the interplay among composition, structure, and ES properties in lead-free relaxor dielectric ceramics, laying the groundwork for innovative advancements in the field.