Ultrahigh energy-storage density of a lead-free 0.85Bi0.5Na0.5TiO3–0.15Ca(Nb0.5Al0.5)O3 ceramic under low electric fields

Abstract

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 Bi_0.5Na_0.5TiO₃ 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)Bi_0.5Na_0.5TiO₃–xCa(Nb_0.5Al_0.5)O₃ (x = 0, 0.05, 0.075, 0.1, 0.15, 0.2) [(1 − x) BNT–xCNA] ceramics were investigated. Remarkably, the 0.85Bi_0.5Na_0.5TiO₃–0.15Ca(Nb_0.5Al_0.5)O₃ ceramic exhibits ultrahigh recoverable energy storage density (W_rec = 4.41 J cm⁻³) and efficiency (η = 88%) at a low electric field (210 kV cm⁻¹). Highly stable dielectric energy storage performance is observed over a wide temperature (20–200 °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_0.5Na_0.5TiO₃–0.15Ca(Nb_0.5Al_0.5)O₃ 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.