Crystallization kinetics of Ba_0.8Sr_0.2TiO₃ sols and sol-gel synthesis of Ba_0.8Sr_0.2TiO₃ thin films

Chemically homogeneous Ba_0.8Sr_0.2TiO₃ (BST) sols were synthesized using barium acetate, strontium acetate, and titanium tetra-n-butoxide as starting materials. The crystallization behaviour of the BST sols and thin films was studied by differential thermal analysis (DTA) and X-ray diffraction (XRD). The kinetics of crystallization was studied by applying the DTA measurement carried out at different heating rates. The effective activation energy of crystallization associated with the formation of perovskite phase was measured as 270.8 kJ mol^-1. The Avrami exponent n (reaction order) is about 1, which suggests that the growth of perovskite phase is diffusion-controlled. The calculated half-life time indicates that the minimum temperature for the crystallization is 600 °C. The BST thin films were prepared on Pt-coated silicon substrates from the sols. The films annealed at 650 °C have good perovskite crystallinity without the existence of second phase.