A co-doping strategy to achieve high energy storage performance in BiFeO₃-based ceramics

In this work, (Bi0.65-0.65xBa0.35-0.35xNdx)(Fe0.65-0.65xTi0.35-0.35xNbx)O3+x (abbreviated as: BFBT-xNN, x = 0, 0.04, 0.08 and 0.12) ceramics were fabricated through a solid-state reaction method, aiming to obtain highperformance capacitor materials. BFBT ceramics have attracted increasing attention as potential energy storage materials because of their excellent dielectric and ferroelectric properties. However, two handicaps limit the large improvement of their energy storage performance (ESP). One is the large hysteresis of their polarization (P)-electric field (E) loops; the other is the low dielectric breakdown strength (Eb), which has a close correlation with the inevitable defects present in BF-based ceramics. Herein, we designed a co-doping strategy to overcome the two handicaps in order to achieve high ESP in BFBT ceramics. In this strategy, the trivalent rare earth Nd3+ ions and high valence Nb5+ ions are simultaneously introduced at the perovskite A- and B-sites of BFBT ceramics, which is called NN co-doping. The NN co-doping enhances the relaxor properties of BFBT ceramics due to the enhanced composition and charge fluctuations and promotes the formation of the Bi-rich phases, which contribute to the appearance of a slim P-E loop. Meanwhile, the Eb of BFBT ceramics is enhanced, which is ascribed to the significantly decreased oxygen vacancy concentration, the reduced grain size and the Bi-rich phases. Benefitting from these factors, a high recoverable energy storage density (Wrec) of 3.64 J/cm3 and energy storage efficiency (& eta;) of 88% are simultaneously obtained under an enhanced Eb of 330 kV/cm in BFBT0.08NN ceramics. Moreover, the ESP of BFBT-0.08NN ceramics shows good thermal stability (30-150 degrees C) and charge-discharge properties. These results indicate that BFBT-0.08NN ceramics could be a promising capacitor material.