Stabilization of Poly(vinylpyrrolidone)‐containing Alkoxide Solutions for Thick Sol‐Gel Barium Titanate Films

The authors previously demonstrated that Ba(CH 3 COO) 2 ‐Ti(OC 3 H 7 i ) 4 ‐CH 3 COOH‐H 2 O‐ i ‐C 3 H 7 OH solutions containing poly(vinylpyrrolidone) (PVP) can offer crack‐free BaTiO 3 coatings >1 μm 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(OC 2 H 5 ) 4 and C 2 H 5 OH instead of Ti(OC 3 H 7 i ) 4 and i ‐C 3 H 7 OH, respectively, high CH 3 COOH contents and low H 2 O contents in solutions were effective in suppressing the variation of viscosity with time. A solution of molar composition, Ba(CH 3 COO) 2 :Ti(OC 2 H 5 ) 4 :PVP:CH 3 COOH:H 2 O:C 2 H 5 OH = 1:1:0.5:27:4:5, exhibited great stability in viscosity over 900 h at room temperature. Crack‐free BaTiO 3 films as thick as 0.9 μm could be obtained via noncycled gel film deposition and firing at 700°C. However, the dielectric constant of the 0.9‐μm‐thick film was as low as 130 at 1 kHz. The films obtained via stepwise firing at 360° and 700°C, on the other hand, were ∼0.6 μm thick, showed good transparency, and had dielectric constants of ∼290 at 1 kHz.