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In this work, (Bi 0.65-0.65 x Ba 0.35-0.35 x Nd x)(Fe 0.65-0.65 x Ti 0.35-0.35 x Nb x)O 3+ x (abbreviated as: BFBT- x NN, x = 0, 0.04, 0.08 and 0.12) ceramics were fabricated through a solid-state reaction method, aiming to obtain high-performance 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 (E b), 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 E b 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 (W rec) of 3.64 J/cm3 and energy storage efficiency (η) of 88% are simultaneously obtained under an enhanced E b of 330 kV/cm in BFBT-0.08NN ceramics. Moreover, the ESP of BFBT-0.08NN ceramics shows good thermal stability (30–150 °C) and charge-discharge properties. These results indicate that BFBT-0.08NN ceramics could be a promising capacitor material. [ABSTRACT FROM AUTHOR]

(1- x)(0.75(Na 0.5 Bi 0.5)TiO 3 -0.25SrTiO 3)- x NdGaO 3 ceramics (NBST- x NG, x = 0–0.06) were fabricated through a solid-state reaction method. High-valent Nd3+ ions enter the perovskite A-site to occupy Bi vacancies resulting from the volatilization of Bi, inhibiting the formation of oxygen vacancies and contributing to an enhanced breakdown electric field (E b). Low-valent Ga3+ ions enter the B-site to substitute for Ti4+ ions, resulting in the formation of random electric fields (REFs) at the B-site due to co-occupying hetero-valence ions of Ga3+/Ti4+, which significantly reduces ferroelectric hysteresis. Therefore, a synergic effect of A- and B-sites co-doping was realized in NBST- x NG ceramics. Benefitting from this synergic effect, an enhanced recoverable energy storage density (W rec) of 2.88 J/cm3 and an efficiency (η) of 83% are simultaneously obtained in NBST-0.04NG ceramics under a moderate electric field (E) of 200 kV/cm. Compared with most NBT-based ceramics, the values of (η vs W rec / E 2) for NBST-0.04NG ceramics show an obvious advantage, indicating excellent potential for application as an energy storage material. Moreover, W rec and η of NBST-0.04NG ceramics exhibit excellent temperature stability from 30 °C to 200 °C due to the enhanced correlation strength of polar nanoregions (PNRs) and local structural stability. This work provides a potential strategy to improve the energy storage performance of NBT-based ceramics via the synergic effect of A- and B-site co-doping. [ABSTRACT FROM AUTHOR]