Sol–gel synthesis and characterization of lead-free Ba0.85Sr0.15TiO3-based thin-film capacitors with enhanced dielectric and energy storage performance

Lead-free Ba_0.85Sr_0.15TiO₃ (BST) thin films ranging in thicknesses from 50 to 600 nm were deposited on platinized silicon (Pt/SiO₂/Si) substrates using a spin-coating technique, successfully creating Au/BST/Pt thin capacitors. X-ray diffraction and scanning electron microscopy revealed that the BST films were crack-free, dense, and crystallized with a polycrystalline tetragonal perovskite structure. The thickness-dependent dielectric, leakage current, ferroelectric, and energy storage properties of Ba_0.85Sr_0.15TiO₃ were analyzed at room temperature. As the BST film thickness increased from 50 to 600 nm, the dielectric permittivity of films also increased from about 40 to over 320, caused by the interfacial dead layers between films and electrodes. In contrast, both the leakage current density and the dielectric losses decreased with increasing film thickness. The figure of merit shows a remarkable enhancement from 7 to 38 with the increase in thickness from 50 to 600 nm. Experimental results indicated that increases in dielectric permittivity and tunability are consistently linked to a low dielectric loss, which practically enhances the figure of merit. Additionally, the study of energy storage performance across different films revealed high and promising values for both efficiency and recoverable energy density. The highest efficiency, 70%, was achieved with a 400 nm film, which also exhibited a significant energy storage density of 7 J/cm³. These BST thin films thus show great potential as materials for manufacturing electrostatic capacitors for electrical energy storage.