High energy storage performance in the Bi_0.5Na_0.5TiO₃–BaTiO₃–Nd(Mg_1/2Hf_1/2)O₃ ternary system with multiscale polymorphic domains and local heterogeneous structure

   Lead-free dielectric relaxor ferroelectric (RFE) ceramics are regarded as one of the promising materials for dielectric energy storage applications. However, the contradiction between high polarization and low hysteresis leads to interior energy storage performance, which greatly limits their applications in high/pulsed power systems. Here, we propose an effective strategy to significantly improve the energy storage properties of 0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ (0.04BNT-0.06BT) with morphotropic phase boundary (MPB) composition by constructing multiscale polymorphic domains and local heterogeneous structure. The introduction of Nd(Mg_1/2Hf_1/2)O₃ (NMH) facilitates the formation of short-range ordered polar nanoregions (PNRs). Meanwhile, small amounts of nanodomains with high polarization are resulted from local heterogeneous structure with Bi- and Ti-rich regions. Multiscale polymorphic domains with the coexistence of rhombohedral/tetragonal (R+T) nanodomains and PNRs ensure both high polarization and low hysteresis, which is very crucial for an improvement of energy storage performance. Furthermore, excellent electric insulation is resulted from high insulation resistivity, grain size in submicron scale and a wide band gap by introducing NMH doping. Therefore, high recoverable energy density (W_rec) of 7.82 J/cm³ with ultrahigh efficiency (h) of 93.1% is realized in the designed BNT-BT-NMH ternary system contributed by both large ΔP and high E_b. These findings together with good temperature/frequency/cycling stability indicate that the optimum composition ceramic is a very promising material for energy storage applications in high/pulsed power systems.