Enhanced energy storage performance in oxygen-deficient Ca_0.28Ba_0.72Nb₂O₆-based tungsten bronze ceramics

The development of high-power technology and modern electronic devices imposes stringent demands on the energy storage performance of capacitors. Achieving an optimal balance between polarization and dielectric breakdown strength is essential for improving energy storage density. This study proposes a strategy to enhance polarization without compromising dielectric breakdown strength by deliberately introducing defects. In this context, a series of non-stoichiometric Ca0.7Ba1.5La0.2Nb5- xFexO15- delta ceramics were prepared. Investigations into the structure and electrical behavior suggested that defects did not stabilize ferroelectricity, rather, they served as sources of random fields and incommensurate modulation structure that enhanced the relaxor behavior. Nevertheless, defects introduced additional polarization, and contributed to the asymmetry of the P-E loops and the fluctuation of the polarization response at high temperature/frequency. Furthermore, the maintenance of high BDS is attributed to the trapping of carriers by defects and the improvement of electrical homogeneity, which is confirmed by defect analysis and complex impedance spectroscopy. As a result, a releasable energy density of 3.42 J/cm3 and an efficiency of 86.23 % are obtained in defect-rich Ca0.7Ba1.5La0.2Nb4.875Fe0.125O15- delta ceramics. Meanwhile, a discharge energy density of 2.24 J/cm3 and a power density of 171.97 MW/cm3 are achieved, which also shows excellent stability to the use environment. This work provides valuable insights into the improvement of the energy storage performance of relaxors and other weakly polar dielectrics.