Enhanced energy storage properties in Sr1.85Ca0.15NaNb5O15-based tungsten bronze ceramics through multicomponent substitution

Lead-free Sr1.85−2xCa0.15+xSmxNaNb5−xHfxO15 (x = 0–0.05) ceramics with tetragonal tungsten bronze structure were synthesized and characterized. Compared with the Sr1.85Ca0.15NaNb5O15 ceramic, the substitutions of even very small amount of Hf4+ in B site and Sm3+ in A site lead to a notable change of the microstructure and relevant dielectric and ferroelectric properties. The most uniform and compact microstructure with fine grains and few defects is obtained for the x = 0.04 compound. For the electrical properties, x = 0.04 compound exhibits the largest dielectric permittivity, low dielectric loss, smallest ferroelectric polarization, largest high-temperature electric resistance, and largest dielectric breakdown strength. The analysis of Raman vibration modes reveals the corresponding local structure change for different compositions. The relation between the cation substitutions and the electrical properties evolution is discussed in detail and the potential of x = 0.04 ceramic for energy storage capacitor is revealed. High total energy storage density (4.7 J/cm3) and recoverable energy storage density (2.7 J/cm3) along with energy storage efficiency (58%) are observed for the x = 0.04 sample at the applied electric field of 430 kV/cm. In addition, good stability of the energy storage property is also obtained for different frequencies. The capacitive performances obtained in this study demonstrate the great potential of tungsten bronze ceramics designed for energy storage applications.