Enhanced energy storage performance of 0.88(0.65Bi0.5Na0.5TiO3-0.35SrTiO3)-0.12Bi(Mg0.5Hf0.5)O3 lead-free relaxor ceramic by composition design strategy

[Display omitted] •The effect of ST and BMH doping in BNT on energy storage properties were studied.•By modifying composition, good energy storage properties are obtained in BNST-BMH.•Ultrahigh Wrec of 5.59 J/cm3and η of 85.3% are realized in BNST-BMH ceramic.•BNST-BMH ceramic exhibits excellent thermal stability from 20 °C to 140 °C.•A superior fatigue resistance over 105 cycles was achieved in BNST-BMH ceramic. Dielectric ceramic capacitors with high energy density are one of the great bright energy storage devices. Here, the Bi0.5Na0.5TiO3, 0.75Bi0.5Na0.5TiO3-0.25SrTiO3, 0.65Bi0.5Na0.5TiO3-0.35SrTiO3 and 0.88(0.65Bi0.5Na0.5TiO3-0.35SrTiO3)-0.12Bi(Mg0.5Hf0.5)O3, (abbreviated as BNT, BNT-25ST, BNT-35ST and BNST-BMH, respectively) ceramics were produced by solid state sintering method. The influence of solid solution of SrTiO3 and Bi(Mg0.5Hf0.5)O3 doping in Bi0.5Na0.5TiO3 on crystal structure, microstructure, electrical and energy storage performance were evaluated systematically. By optimizing ceramics composition, high breakdown field and slim hysteresis loops were simultaneously realized due to enhanced band gap, refined grain size and nano-domains formed, which can be verified by the transmission electron microscope (TEM), piezoelectric force microscope (PFM) and ultraviolet–visible spectrum. Therefore, an ultrahigh recoverable energy density of 5.59 J/cm3 with brilliant efficiency of 85.3% is realized in BNST-BMH ceramic. Besides, the BNST-BMH also exhibits prominent temperature stability at 20–140 °C, superior fatigue resistance beyond 105 cycles and outstanding frequency stability at 1–200 Hz. Our work offers a novel way for designing dielectric capacitors and also proves that BNST-BMH is indeed a great hopeful dielectric energy storage material in pulse power electronics.