Stabilization of poly(vinylpyrrolidone)-containing alkoxide solutions for thick sol-gel barium titanate films

The authors previously demonstrated that Ba(CH3COO)(2)- Ti(OC3H7i)(4)-CH3COOH-H2O-i-C3H7OH solutions containing poly(vinylpyrrolidone) (PVP) can offer crack-free BaTiO3 coatings >1 mum thick via noncycled, single-step dip coating. The solutions, however, gelled. within a few hours, which cannot be of practicable use in industry. To make the solutions applicable for industrial use, the solution composition has been optimized so that the solutions have sufficient stability in viscosity. Using Ti(OC2H5)(4) and C2H5OH instead of Ti(OC3H7i)(4) and i-C3H7OH, respectively, high CH3COOH contents and low H2O contents in solutions were effective in suppressing the variation of viscosity with time. A solution of molar composition, Ba(CH3COO)(2): Ti(OC2H5)(4):PVP:CH3COOH:H2O:C2H5OH = 1:1:0.5:27:4:5, exhibited great stability in viscosity over 900 h at room temperature. Crack-free BaTiO3 films as thick as 0.9 mum could be obtained via noncycled gel film deposition and firing at 700degreesC. However, the dielectric constant of the 0.9-mum-thick film was as low as 130 at I kHz. The films obtained via stepwise firing at 360degrees and 700degreesC, on the other hand, were similar to0.6 mum thick, showed good transparency, and had dielectric constants of similar to290. at 1 kHz.