Influence of cation substitution on the phase formation kinetics of Sr_0.7Bi_2.3Ta₂O₉ thin films

The Ta⁵⁺ ions in sol-gel derived Sr_0.7Bi₂₃Ta₂O₉(SBT) thin films were partially substituted by Zr⁴⁺ to form Sr_0.7Bi_2.3Ta_1.7Zr_0.3 0₉ (SBTZ) thin films and Aurivillius phase formation characteristics were compared for each thin film. X-ray diffraction (XRD) analyses were performed on the thin films heated in the range of 730-760 °C at 10 °C intervals and it was found that phase formation and crystal growth were greatly affected by the film composition and crystallization temperature. Johnson-Mehl-Avrami (JMA) isothermal kinetic analyses were performed on the XRD results and activation energy and Avrami exponent values were determined for the fluorite-to-Aurivillus phase transformation. A reduction of ∼82 kJ/mol in activation energy was observed for the SBTZ thin films, which revealing the key reason of enhanced kinetics in SBTZ. XRD and scanning electron microscopy (SEM) showed the remaining of fluorite phase in SBT and the formation of a secondary phase in SBTZ.