Remarkable improvement of energy storage performance of Gd₂O₃-doped BNT-based relaxor ferroelectric ceramics

Bi_0.5Na_0.5TiO₃ (BNT) is a lead-free ferroelectric ceramic that has received much attention in recent years. However, the pure BNT presents a tetragonal structure with considerable remanent polarization at room temperature, which lead to its low energy storage efficiency thus limiting its application in energy storage. In this paper, on the basis of the introduction of Ba_0.3Sr_0.7TiO₃ (BST), NaNbO₃ (NN) into BNT to form a relaxor ferroelectric, Gd₂O₃ is further doped to refine grain and reduce oxygen vacancy concentration thereby improving the breakdown strength, which is beneficial to improve its energy storage performance. A series of ceramic samples of 0.9 (0.5BNT-0.5BST)-0.1NN + xwt%Gd (x = 0, 0.5, 1, 2.5, 3) were prepared by the solid-state reaction method. The effect of Gd₂O₃ on the microstructure and electrical properties of the systems was investigated. The results show that a suitable doping level of Gd₂O₃ can significantly refine the grains and improve the breakdown strength of the system. For x = 2.5 ceramic sample obtained a high energy storage density of W_rec = 4.86 J/cm³ and an energy storage efficiency of η = 86% at 250 kV/cm. Furthermore, this sample exhibited a stable discharge density (W_d ≥ 1.44 J/cm³) and an ultra-fast discharge rate (t_0.9 ≤ 0.056 µs) in the temperature range of 140 kV/cm, 40∼140 °C.