Multiscale microstructure engineering enables simultaneous enhancement of energy storage and efficiency lead-free ceramics

The rising demand for high-power-density capacitors in hybrid electric vehicles and advanced microelectronics calls for lead-free dielectric ceramics with both high energy storage density (W_rec) and efficiency (η). Yet, achieving concurrent enhancement of these properties remains a key challenge. Here, we report a performance breakthrough in a 0.6(Bi_0.5Na_0.4K_0.1)TiO₃-(0.4–x)SrTiO₃-xBa_0.7La_0.2(Sn_0.5Ti_0.5)O₃ (BS-xBLST) solid solution system via a multiscale microstructure engineering strategy. Ba²⁺/La³⁺ co-doping introduced A-site vacancies and nanoscale compositional fluctuations that enhanced relaxor-like behavior and polarization reversibility. Optimizing the BLST/SrTiO₃ ratio stabilized Bi³⁺ content, maintaining strong intrinsic polarization while suppressing large domain growth. Additionally, Sn⁴⁺ doping effectively reduced grain size, leading to improved dielectric breakdown strength. By integrating microstructural modifications across multiple length scales, ranging from unit-cell distortions to grain-boundary engineering, the optimized ceramic achieved a high W_rec of 9.18 J/cm³ and a superior η of 93.85% under 650 kV/cm, with excellent thermal stability from 30 to 160 °C. These enhancements stem from nanoscale polar heterogeneity and structurally stabilized polar nanoregions. The results demonstrate a versatile design strategy for lead-free dielectric ceramics and provide key insights into the relationship between hierarchical structure and macroscopic dielectric behavior.