Ultrahigh energy-storage density of a lead-free 0.85Bi_0.5Na_0.5TiO₃-0.15Ca(Nb_{0.5Al0.5)O3 ceramic under low electric fields}

The low energy density of dielectric ceramics at low electric fields is a limiting factor for their application in size-reduced integrated electronic devices. In this work, (Nb5+ + Al3+) and Ca2+ ion doped Bi0.5Na0.5TiO3 ceramics possessing high energy storage density at low electric fields were prepared. The microstructure, dielectric properties, energy storage and pulsed charge/discharge properties of the (1 - x)Bi0.5Na0.5TiO3-xCa(Nb0.5Al0.5)O-3 (x = 0, 0.05, 0.075, 0.1, 0.15, 0.2) [(1 - x) BNT-xCNA] ceramics were investigated. Remarkably, the 0.85Bi(0.5)Na(0.5)TiO(3)-0.15Ca(Nb0.5Al0.5)O-3 ceramic exhibits ultrahigh recoverable energy storage density (W-rec = 4.41 J cm(-3)) and efficiency (eta = 88%) at a low electric field (210 kV cm(-1)). Highly stable dielectric energy storage performance is observed over a wide temperature (20-200 degrees C) and frequency (10-500 Hz) range. In addition, a high power density (P-d) of 49.8 WM cm(-3) and a fast charge/discharge rate (t(0.9) = 61.2 ns) can be achieved simultaneously. The excellent properties of the lead-free 0.85Bi(0.5)Na(0.5)TiO(3)-0.15Ca(Nb0.5Al0.5)O-3 ceramics originated from the P4bm polar nanoregions (PNRs), enhanced band gaps and refined grains in the modified non-homogeneous structure. The results show that the composite ion substitution strategy is an effective way to achieve high energy storage performance of BNT-based ceramics at low electric fields.