Significantly improving the energy storage capability of transparent ceramics via a voltage endurance double enhancement strategy

•A voltage endurance double enhancement strategy was employed to reach a high Eb.•Polarization’s reduction during the relaxor-to-linear phase transition was mitigated.•An ultra-high Wrec of 7.62 J/cm3 with an η of 86.06 % was reached. While epitaxial thin films and polymer films exhibit superior voltage endurance and higher maximum polarization (Pmax), making them advantageous for achieving high energy storage density (Wrec), ceramic bulk materials remain the most promising candidates for the industrialization of dielectric energy storage capacitors. In this study, Bi(Mg2/3Ta1/3)O3 (BMT) was incorporated into the 0.8 K0.5Na0.5NbO3-0.2Ba0.9Ca0.1Zr0.15Ti0.85O3 (KNN-BCZT) lattice, resulting in a transition from a relaxor ferroelectric to a linear dielectric state. Concurrently, the ceramic structure transitioned from a coexistence of tetragonal (T) and orthorhombic (O) phases to a single O-phase, accompanied by an unexpected observation of the liquid phase. Though the former decreases the polarization, which inevitably leads to some deterioration in Wrec, the two behaviors in the latter both have positive effects on increasing the electric breakdown strength (Eb), a voltage endurance double enhancement behavior thus occurs on 0.90KNN-BCZT-0.10BMT, and an ultra-high Wrec of 7.62 J/cm3 with an η of 86.06 % was reached. Moreover, carefully controlling the transition temperature (Tm) ensured excellent energy storage reliability, with a degradation of less than 8 % after 106 cycles at both 25 °C and 200 °C. The 0.90KNN-BCZT-0.10BMT ceramic also demonstrated fast discharge performance with a t0.9 of only 89 ns. In conclusion, this work introduces a voltage endurance double enhancement strategy to mitigate the Wrec reduction during the relaxor-to-linear phase transition, offering a novel approach for fabricating high-energy density capacitors.