High energy storage performance of (1-x)Ba0.5Sr0.5TiO3-xK0.5Na0.5NbO3 ceramics via a combined strategy of fine grains and multiphase polar nanoregions.

• A novel (1- x)BST– x KNN lead-free relaxor ceramic system was proposed. • Coexistence of multiphase PNRs contributed to the linearization of the P-E loops. • Ultrafine grains in the ceramics greatly improved the E b. • High energy storage performances were achieved in 0.7BST-0.3KNN. Electrostatic dielectric capacitors have received great attention due to their ultrafast charging-discharging speed and ultrahigh power density. However, the low energy storage density and efficiency are the main obstacles to their practical applications. In this work, solid solution relaxor ceramics with different proportions of lead-free ferroelectrics Ba 0.5 Sr 0.5 TiO 3 (BST) and K 0.5 Na 0.5 NbO 3 (KNN) were prepared. Superior energy storage performance was achieved in the 0.7BST-0.3KNN ceramics with a breakdown strength (E b) of 510 kV/cm, a recoverable energy storage density (W rec) of 4.10 J/cm3, and an energy storage efficiency (η) of 80 %, which was fairly stable over the temperature range of 30–100 °C. Since multiple cations with different valence and radius coexist on the equivalent sites (A or B sites) of the solid solutions, the chemical disorder and the corresponding lattice distortion induced the coexistence of cubic, tetragonal, and orthorhombic phases, as well as the appearance of the multiphase polar nanoregions (PNRs), making the ferroelectric hysteresis loops linear. At the same time, ultrafine grains in the ceramics greatly improved the E b. For achieving excellent energy storage performance, this work demonstrates a potential candidate of (1- x)BST- x KNN lead-free solid solution ceramics and a combined strategy of fine grains and multiphase PNRs. [ABSTRACT FROM AUTHOR]