Multiscale structural engineering enables superior energy storage in tetragonal tungsten bronze relaxor ferroelectrics

Lead-free relaxor ferroelectric ceramics are promising for pulsed-power systems due to their ultrafast discharge and high-power density, yet their practical use remains limited by low breakdown strength and insufficient energy-storage density. Here, we report Ba₂La_1−xBi_xTi₂Nb₃O₁₅ ceramics with a tetragonal tungsten bronze structure, which achieve a recoverable energy density of 14.39 J/cm³ and an efficiency of 87.69% under an ultrahigh field of 1400 kV/cm–one of the highest recoverable energy density values reported for bulk tetragonal tungsten bronze structured ceramics. By combining experiments, first-principles calculations, and finite-element simulations, we unravel a multiscale structural optimization mechanism. Bi³⁺ incorporation induces oxygen-octahedral distortion that disrupts long-range order and enhances relaxation behavior. Concurrent grain refinement and band gap widening substantially raise the breakdown strength, leading to superior energy-storage properties. Moreover, the material exhibits excellent stability against variations in temperature, frequency, and fatigue cycles. This work establishes a generally applicable multiscale structural-engineering strategy for tetragonal-tungsten-bronze dielectrics with high energy storage performance.