Enhanced energy storage properties of KNbO₃ modified (Bi_0.5Na_0.5)TiO₃-BaTiO₃ based lead-free relaxor ferroelectric ceramics

Dielectric capacitors are widely used in pulse devices because of their fast charge/discharge speed. However, the low energy storage density limits their application. In this work, (1 − x)(Bi_0.5Na_0.5)_0.94Ba_0.06Ti_0.99(Y_0.5Nb_0.5)_0.01O₃-xKNbO₃ (BNBTYN-100xKN) lead-free relaxor ferroelectric ceramics were fabricated via a solid-state sintering technique. K⁺ and Nb⁵⁺ were completely diffused into the BNBTYN lattice and formed solid solutions. The incorporation of KNbO₃ reduced the symmetry of BNBTYN-100xKN ceramics and destroyed the long-range ordered ferroelectric domains, leading to thinning of hysteresis loops. The relaxor degree increased with the KN content, resulting in the improvement of efficiency. Therefore, using BNBTYN-5KN ceramics an energy storage density of 1.246 J cm⁻³ and an efficiency of 78.7% at 104 kV cm⁻¹ were obtained. In addition, the BNBTYN-5KN ceramics exhibited this energy storage density with outstanding temperature stability (in the range of 20-120 °C) and excellent fatigue resistance. These results reveal that BNBTYN-5KN ceramics is a promising material for energy storage.