Superior energy storage performance and transparency in (K0.5Na0.5)(Nb0.97Ta0.03)O3-based ceramics†

Lead-free transparent ferroelectric ceramics are an ideal material to meet the needs of pulsed power technology and optical transparency because of their excellent optical transparency and energy storage performances. However, it is difficult for lead-free ceramics to have both high energy storage performance and high optical transmittance, which limits the development of high-performance and multifunctional devices. Through this paper, we propose a method to construct strong relaxor ferroelectric KNN-based ceramics with nano-domains by adding Sr²⁺, Li⁺ and Nb⁵⁺, which greatly improves the transparent energy storage performance. By introducing appropriate amounts of Sr²⁺, Li⁺ and Nb⁵⁺, the sintering temperature is lowered; therefore, the growth of grains is inhibited. Fine rectangular grains and nanoscale domains are formed. The uneven distribution of potassium and sodium relieves the over-concentration of the electric field and ensures that the ceramics do not decompose under a high electric field. The 0.7(K_0.5Na_0.5)(Nb_0.97Ta_0.03)O₃–0.10LiNbO₃–0.20SrCO₃ ceramic has an ultra-high recoverable energy storage density (W_rec) of 5.9 J cm⁻³, excellent energy storage efficiency (η) of 84.2%, large dielectric breakdown strength (E_b) of 490 kV cm⁻¹, high hardness value of 7.57 GPa, and good light transmittance of 43.0% (at 900 nm). Additionally, excellent temperature and frequency stability are obtained. The dense microstructure, nanoscale grains, symmetrical lattice structure, and strong relaxation behavior are the main reasons for obtaining high energy storage, hardness, and transparency properties.