Simultaneously achieved high‐energy storage density and efficiency in (K,Na)NbO3‐based lead‐free ferroelectric films.

With the development of advanced electrical and electronic devices and the requirement of environmental protection, lead‐free dielectric capacitors with excellent energy storage performance have aroused great attention. However, it is a great challenge to achieve both large energy storage density and high efficiency simultaneously in dielectric capacitors. This work investigates the energy storage performance of sol‐gel‐processed (K,Na)NbO3‐based lead‐free ferroelectric films on silicon substrates with compositions of 0.95(K0.49Na0.49Li0.02)(Nb0.8Ta0.2)O3‐0.05CaZrO3‐x mol% Mn (KNN‐LT‐CZ5‐x mol% Mn). The appropriate amount of Mn‐doping facilitates the coexistence of orthorhombic and tetragonal phases, suppresses the leakage current, and considerably enhances the breakdown strengths of KNN‐LT‐CZ5 films. Consequently, large recoverable energy storage density up to 64.6 J cm−3 with a high efficiency of 84.6% under an electric field of 3080 kV cm−1 are achieved in KNN‐LT‐CZ5‐5 mol% Mn film. This, to the best of our knowledge, is superior to the majority of both the lead‐based and lead‐free films on silicon substrates and thus demonstrates great potentials of (K,Na)NbO3‐based lead‐free films as dielectric energy storage materials. [ABSTRACT FROM AUTHOR]