Enhanced energy density and discharged efficiency of lead-free relaxor (1-x)[(Bi0.5Na0.5)0.94Ba0.06]0.98La0.02TiO3-xKNb0.6Ta0.4O3 ceramic capacitors

Ceramic capacitors have optimistic application prospects in the field of high power density energy storage. However, most of the investigations have sought to increase energy storage density (W), but ignore the importance of energy storage efficiency (η). In this work, the novel KNb0.6Ta0.4O3-modified [(Bi0.5Na0.5)0.94Ba0.06]0.98La0.02TiO3 ceramics were designed and prepared. Particularly, the long-range order of ferroelectricity for the ceramic is broken due to the addition of KNb0.6Ta0.4O3 (KNT), which causes shoulder dielectric peak (Ts) to move towards low temperatures and increases the content of weakly polar phase. Therefore, the remanent polarization Pr is effectively decreased, but the large saturation polarization Ps is maintained, leading to simultaneously high η and large W. Moreover, the addition of KNT significantly reduces the grain size, causing an enhanced dielectric breakdown strength (DBS). As a result, ultra-high values for η of 92.9% and Wrec of 2.1 J/cm3 are realized in the ceramic with x = 0.10, which are superior to most of the reported ceramic capacitors under the similar electric field. More importantly, the ceramic exhibits excellent thermal (25–150 °C) and frequency stability (5–105 Hz). The present strategy of adjusting the Ts and weakly polar phase provides a promising approach to design novel Bi0.5Na0.5TiO3-based materials with excellent energy storage performance.