Realizing Exceptional Energy Storage Performance in Tungsten Bronze-Based Ceramics via Weakly Coupled Relaxor and Grain Boundary Reinforcement Designs

Dielectric ceramic capacitors play a crucial role in next-generation pulse power systems due to their high power density and rapid charge and discharge capabilities. However, significant challenges persist in achieving large recoverable energy storage density (W_rec). In this work, a tungsten bronze relaxor ferroelectric ceramic is designed based on Sr_0.6Ba_0.4Nb₂O₆ (SBN), which exhibits a significant W_rec of approximately 8.74 J·cm^–3 and a high efficiency (η) of about 90.9% at 740 kV·cm^–1. Structural characterizations reveal that the introduction of Bi³⁺ and Fe³⁺ refines the crystal structure and induces substantial incommensurate modulation in the tetragonal tungsten bronze (TTB) lattice, resulting in the emergence of weakly coupled polar nanoregions (PNRs) and enhancing the relaxor behavior. Moreover, the CuO that aggregates near the grain boundary results in a reinforced grain boundary and improves the breakdown field strength (E_BDS). This study presents a competitive TTB-based lead-free relaxor ferroelectric ceramic and expands the range of materials available for advanced dielectric ceramic capacitor applications.