Simultaneous enhancement of the energy storage, transparency, and hardness properties of K0.5Na0.5NbO3-based ceramics via a synergistic optimization strategy

Abstract

The development of dielectric capacitors with good overall performance is urgently needed to meet the growing demand for multifunctional energy storage devices. However, most high-energy storage ceramics rely on large polarization or electric field strength, and it is challenging to integrate these with other properties, such as high transparency or hardness. This study achieves a synergistic optimization of energy storage performance, optical transparency, and mechanical hardness under a moderate-strength electric field by designing a (1 − x)(K_0.5Na_0.5)NbO₃–x(Bi(Zn_0.5Nb_0.4)O₃) (KNN–BZN) ceramic. The results show that a high recoverable energy storage density (W_rec = 2.65 J cm⁻³), energy storage efficiency (η = 85.96%) and optical transmittance (66%) were obtained under a moderate electric field when x = 0.15. The introduction of BZN had a significant effect on the microstructure and relaxation of the KNN-based ceramics, leading to a decrease in grain size, denser ceramics, and prompting the formation of polar nano-regions (PNRs). Meanwhile, the bandgap of 0.85KNN-0.15BZN is shown to be the largest from first-principles calculations, with a value of about 2.72 eV, and a high hardness of 13.12 GPa is obtained. These results indicate that KNN–BZN lead-free ferroelectrics have a promising future in the field of multifunctional energy storage ceramics.