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 (Δ P ) 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 0.5 Na 0.4 K 0.1 )TiO 3 - x (Sr 0.85 La 0.1 )(Zr 0.5 Ti 0.5 )O 3 (BNKT- x SLZT), 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 Δ P . Ultimately, enhanced ES performance is demonstrated in BNKT-0.15SLZT VPP, achieving a remarkable W rec of 6.85 J/cm 3 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/cm 3, a large power density of 164.2 MW/cm 3, 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.