Single-layer submicron-thick BaTiO₃ coatings from poly(vinylpyrrolidone)-containing sols: Gel-to-ceramic film conversion, densification, and dielectric properties

BaTiO₃-coating films were prepared from a solution containing poly(vinylpyrrolidone) (PVP) of molar composition Ba(CH₃COO)₂:Ti(OC₂H₅)₄:PVP:CH₃COOH:H₂O: C₂H₅OH = 1:1:0.5:27:4:5, via nonrepetitive, single-step dip-coating. The gel films were found to be converted into BaTiO₃ films via evaporation of the solvent and CH₃COOH below 210 °C, decomposition of PVP at 210–360 °C, decomposition of CH₃COO⁻ below 440 °C, and crystallization at 500–610 °C. The decomposition of PVP was accompanied by the progress of the condensation reaction, which resulted in significant reduction in film thickness. When the gel films were heated isothermally at 700 °C, crack-free BaTiO₃ films as thick as 0.9 μm were obtained. When the gel films were heated isothermally at 360 °C and then at 700 °C, the film became denser. Higher dielectric constants around 290 were found for the film that underwent the isothermal heat treatment at 360 °C. A slower rate of PVP decomposition was thought to be the key for the film densification.