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<p>Developing high-performance lead-free energy storage ceramics requires the synergistic optimization of recoverable energy storage density (<i>W</i><sub><i>rec</i></sub>), efficiency (<i>η</i>), and thermal stability. In this study, (K<sub>0.5</sub>Na<sub>0.5</sub>)NbO<sub>3</sub> doping was employed to modulate the relaxor properties of 0.4(Bi<sub>0.5</sub>Na<sub>0.5</sub>)TiO<sub>3</sub>-0.6(Sr<sub>0.7</sub>Bi<sub>0.2</sub>)TiO<sub>3</sub> (0.4BNT-(0.6-<i>x</i>)BST-<i>x</i>KNN, <i>x</i> = 0.00–0.06), successfully shifting the dielectric phase transition temperature (<i>T</i><sub><i>m</i></sub>) to near-ambient conditions (<i>T</i><sub><i>m</i></sub>≈25&#xa0;°C for <i>x</i> = 0.04) while stabilizing and enhancing the dynamics of the two-phase coexistence ‘‘slush polar state.’’ This strategy elevates performance through cooperative mechanisms: reduced ferroelectric (P4bm) phase proportion coupled with increased paraelectric (Pm3m) phase fraction collectively generates highly dynamic polar nanoregions (PNRs) and suppresses their spatial correlations, thereby continuously improving <i>η</i>; concomitantly, the maximized relaxation magnitude (<i>Δεᵣ</i>/<i>εₘ</i>) enabled by room-temperature <i>T</i><sub><i>m</i></sub> positioning significantly enhances PNRs structural adaptability, thus optimizing <i>W</i><sub><i>rec</i></sub>. The optimized composition (<i>x</i> = 0.04) achieves exceptional integrated performance at 250&#xa0;kV/cm: <i>W</i><sub><i>rec</i></sub> = 4.37&#xa0;J/cm<sup>3</sup> and <i>η</i> = 91.37%, while maintaining stability across 20 to 160&#xa0;℃ and 0.5 to 100&#xa0;Hz. This work demonstrates that relaxor engineering governing <i>T</i><sub><i>m</i></sub> and PNRs dynamics is an effective strategy for enhancing lead-free ceramic energy storage, offering critical physical mechanistic insights for designing high-performance relaxor ferroelectric dielectrics.</p>

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Co-optimization of relaxor degree and slush polar state for high-energy storage properties in BNT-based ceramics

  • 期刊论文

  • 发表日期：

    2025年9月11日

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  • Huifang Cheng,
  • Changrong Zhou,
  • Qingning Li,
  • Xiaoxiao Xing,
  • Changlai Yuan,
  • Guanghui Rao

摘要

Developing high-performance lead-free energy storage ceramics requires the synergistic optimization of recoverable energy storage density (Wrec), efficiency (η), and thermal stability. In this study, (K0.5Na0.5)NbO3 doping was employed to modulate the relaxor properties of 0.4(Bi0.5Na0.5)TiO3-0.6(Sr0.7Bi0.2)TiO3 (0.4BNT-(0.6-x)BST-xKNN, x = 0.00–0.06), successfully shifting the dielectric phase transition temperature (Tm) to near-ambient conditions (Tm≈25 °C for x = 0.04) while stabilizing and enhancing the dynamics of the two-phase coexistence ‘‘slush polar state.’’ This strategy elevates performance through cooperative mechanisms: reduced ferroelectric (P4bm) phase proportion coupled with increased paraelectric (Pm3m) phase fraction collectively generates highly dynamic polar nanoregions (PNRs) and suppresses their spatial correlations, thereby continuously improving η; concomitantly, the maximized relaxation magnitude (Δεᵣ/εₘ) enabled by room-temperature Tm positioning significantly enhances PNRs structural adaptability, thus optimizing Wrec. The optimized composition (x = 0.04) achieves exceptional integrated performance at 250 kV/cm: Wrec = 4.37 J/cm3 and η = 91.37%, while maintaining stability across 20 to 160 ℃ and 0.5 to 100 Hz. This work demonstrates that relaxor engineering governing Tm and PNRs dynamics is an effective strategy for enhancing lead-free ceramic energy storage, offering critical physical mechanistic insights for designing high-performance relaxor ferroelectric dielectrics.