Ferroelectric-Relaxor Crossover and Energy Storage Properties in Sr₂NaNb₅O₁₅-Based Tungsten Bronze Ceramics

Filled and unfilled Sr₂NaNb₅O₁₅-based tungsten bronze ceramics based on Gd doping were prepared using a traditional solid-state reaction method. Relaxor behaviors of the two different systems were analyzed, and the corresponding energy storage performance was also characterized. With the support of weakly coupled polar nanoregions and a non-polar matrix, an energy storage density of 2.37 J/cm³ and an efficiency of 94.4% were obtained in the Sr_1.82Gd_0.12NaNb₅O₁₅ ceramic. A discharge energy density of 2.51 J/cm³ and a power density of 59.1 MW/cm³ further proved its prospect for practical applications. In addition, the thermal stability and fatigue resistance of the ceramic were also evaluated. At the same time, under the theoretical framework of a perovskite and tungsten bronze, the contribution of vacancies to the local structure and relaxor behavior was briefly discussed. Because the currently used ceramics do not contain easily reducible metal oxides, this work lays the foundation for the development of multilayer ceramic capacitors that use base metals as internal electrodes.