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)NbO 3 -based lead-free ferroelectric films on silicon substrates with compositions of 0.95(K 0.49 Na 0.49 Li 0.02 )(Nb 0.8 Ta 0.2 )O 3 -0.05CaZrO 3 - 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)NbO 3 -based lead-free films as dielectric energy storage materials.