Effect of processing temperature on the morphology of hydrothermally derived barium titanate/polymer thin films

Thin-film composites of BaTiO3 particles in a polymeric matrix were processed by reacting films of a titanium alkoxide, mixed with a polybutadiene-polystyrene triblock copolymer, in aqueous solutions of 1.0 M Ba(OH)(2) at temperatures ranging from 60 to 90 degrees C. After reaction, the composite films displayed distinct surface and subsurface morphologies. The film surface consisted of a continuous layer of BaTiO3 grains, the film grain size decreasing from 180 to 60 nm as the reaction temperature increased from 60 to 90 degrees C. The subsurface growth of BaTiO3 depended on the presence of a percolating network of hydrolyzed titanium alkoxide, which enabled the reaction solution to permeate throughout the thin film. The resulting subsurface film morphology was composed of segregated regions of BaTiO3 particles dispersed throughout the polymeric matrix. The growth of subsurface BaTiO3 particles appeared to be constrained by the polymer matrix, resulting in a subsurface particle size of approximately 5 to 10 nm that was independent of the hydrothermal processing temperature. The reacted films displayed a dielectric constant ranging from 10 to 15 at room temperature and a frequency of 10 kHz.