Superior energy storage in Sn-doped BaTiO3 thin-film capacitors with a slush-like polar state

• Sn-doped BaTiO 3 thin films achieve 105 J cm −3 energy density and 80 % efficiency. • Films exhibit a figure-of-merit of 1125 J cm −3 and stable performance from 0 to 140 °C. • High breakdown strength attributed to Ti 3+ absence and slush-like polar nanodomains. • Polar nanodomains (2–4 unit cells) show large displacements and Sn-deficiency. • Lead-free BTSn films offer eco-friendly energy storage with long-term reliability. Relaxor ferroelectrics are highly valued in energy storage for their high recoverable energy density and efficiency. To address environmental concerns over lead-based materials, this study explores Sn-doped BaTiO 3 (BaTi 0.89 Sn 0.11 O 3 , BTSn) thin films as a lead-free alternative. BTSn films, grown via pulsed laser deposition on a SrTiO 3 substrate with a LaNiO 3 electrode, achieve 105 J cm −3 energy density and 80 % efficiency at 8.5 MV cm −1 , with a figure-of-merit of 1125 J cm −3 at 6 MV cm −1 . They also demonstrate excellent thermal stability (0–140 °C) and durability through 10 10 charge–discharge cycles. The high breakdown strength was attributed to the absence of Ti 3+ and the presence of nanodomains (1–3 nm) with slush-like polar structures. A correlation between the local Sn content and B-site displacement indicates that polar nanodomains, measuring 2–4 unit cells in size, exhibit large displacements and are Sn-deficient. These findings suggest that BTSn thin films offer a promising, reliable, and eco-friendly alternative for next-generation energy storage systems, contributing to global sustainability efforts by reducing reliance on hazardous lead-based materials.