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 Sr1.82Gd0.12NaNb5O15 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.