(1-x)[0.90NN-0.10Bi(Mg2/3Nb1/3)O3]-x(Bi0.5Na0.5)0.7Sr0.3TiO3 ceramics with core–shell structures: A pathway for simultaneously achieving high polarization and breakdown strength

Modern electronics and electrical power systems demand a large energy storage density (Wrec), high efficiency (η), and board operating temperature to deliver high performance. Nevertheless, the inverse correlation between polarization and dielectric breakdown strength hinders Pb-free dielectric ceramics from providing sufficient energy density and consequently limits their practical applications. This study demonstrates the effectiveness of (1-x)[0.90NN-0.10Bi(Mg2/3Nb1/3)O3]-x(Bi0.5Na0.5)0.7Sr0.3TiO3 (abbreviated as xBNST) ceramics with a core−shell structure in overcoming these challenges. Phase-field simulations reveal that the existence of a polar core in the grain effectively reduces the local electric field distribution of the weak polar shell, thereby significantly improving the breakdown strength. Further analyses of intrinsic electronic structure reveal the intrinsic mechanism for enhancing the breakdown strength via first-principles calculations based on density functional theory. Accompanied by the unique structure, grain inhomogeneity featuring the coexistence of strong polar and weak polar clusters contributes to the enhancement of the polarization difference. Consequently, the ceramics exhibit comprehensive energy storage performances [high Wrec = 7.72 J/cm3, large η = 83.78%, and broad usage temperature range (between −40 and 200 °C)]. These findings are expected to provide a feasible way to develop high-performance capacitors for advanced energy storage materials and applications.