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

Abstract 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 Ba 2 La 1 − x Bi x Ti 2 Nb 3 O 15 (BLBTN- x ) ceramics with a tetragonal tungsten bronze structure, which achieve a recoverable energy density of 14.39 J/cm 3 and an efficiency of 87.69% under an ultrahigh field of 1400 kV/cm—the highest performance reported in this material family. By combining experiments, first-principles calculations, and finite-element simulations, we unravel a multiscale structural optimization mechanism. Bi 3+ incorporation induces oxygen-octahedral distortion that disrupts long-range order and enhances relaxation behavior. Concurrent grain refinement and bandgap 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 viable design strategy for tetragonal-tungsten-bronze dielectrics with superior energy-storage performance.