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 degreesC, decomposition of PVP at 210-360 degreesC, decomposition of CH3COO- below 440 degreesC, and crystallization at 500-610 degreesC. 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 degreesC, crack-free BaTiO3 films as thick as 0.9 mum were obtained. When the gel films were heated isothermally at 360 degreesC and then at 700 degreesC, the film became denser. Higher dielectric constants around 290 were found for the film that underwent the isothermal heat treatment at 360 degreesC. A slower rate of PVP decomposition was thought to be the key for the film densification.