Octahedral-rigidity-engineered linear dielectrics for harsh-temperature energy storage capacitors

Next-generation dielectric energy storage technologies, spanning renewable energy systems, electrified transportation, and advanced propulsion platforms, necessitate stable operation under extreme thermal conditions. However, the inherent trade-off between high capacitive performance and thermal stability in existing dielectric materials imposes a critical bottleneck on their practical deployment. Here we engineer an octahedrally rigid framework by 1:2 B-site ordering (Mg/Nb) within an ABO₃ perovskite structure, synergistically coupled with Sr/Bi A-site chemistry to lock structure rigidity and tailor polarizability, culminating in a high-symmetry dual-cubic phase matrix for harsh-temperature capacitive energy storage. Finite-temperature ab initio molecular dynamics simulations combined with density functional theory analysis demonstrate the retention of cubic symmetry with minimal lattice expansion up to 500  °C, consistent with the temperature-stable permittivity and bandgap required for ultra-wide-temperature capacitive energy storage. Further experiments confirm the outstanding energy storage of Sr_0.7Bi_0.2Mg_1/3Nb_2/3O₃ dielectrics, achieving an energy density of 2.2 J cm^-3 and an efficiency of 84% at 270 °C under 800 kV cm^-1, alongside a remarkable enhancement in energy density from 3.0 J cm^-3 (96.5% efficiency) to 4.9 J cm^-3 at 1150 kV cm^-1 enabled by the cold sintering process. The symmetry-driven design, rooted in a cubic matrix, provides critical insight into achieving capacitors with both high energy density and thermal stability under harsh operating conditions.