Excellent energy storage performance of (Sc0.5Ta0.5)4+ modified (Bi0.5Na0.5)TiO3-based ceramics modulated by the evolution of polar phases

To address the environmental pollution and energy crisis in the world, the next generation of advanced pulsed power capacitors has been developed rapidly in recent years, which require lead-free dielectric ceramics with excellent energy storage performance. Herein, we propose a strategy to optimize the energy storage performance of (Bi0.5Na0.5)TiO3-based ceramics via exploring a high saturation polarization which could be modulated by the evolution of oxygen vacancies and local polar phases induced by chemical modification. A high saturation polarization could be maintained in (Sc0.5Ta0.5)4+ doped (Bi0.5Na0.5)TiO3-0.30SrTiO3 (BNST) ceramics, which is ascribed to the increased content of the rhombohedral phase with higher polarization anisotropy. Besides, the incorporation of (Sc0.5Ta0.5)4+ also concurrently induces smaller-sized polar nano-regions and widens the band gap, thereby achieving a stronger relaxor state and larger breakdown electric field. As a result, an ultrahigh recoverable energy density Wrec of 12.2 J cm−3, an excellent efficiency η of 85.9%, and superior energy storage thermal stability (Wrec = 4.4 ± 0.1 J cm−3, η = 89.9 ± 0.9%, 20–140 °C) are obtained in the 20 mol% (Sc0.5Ta0.5)4+ doped BNST ceramic. The present experimental and theoretical systematic studies provide a novel avenue and paradigm for the development of dielectric ceramic materials with ultrahigh energy storage properties.