Enhanced Aurivillius phase formation kinetics in seeded SBT thin films

Strontium bismuth tantalate thin films having composition of Sr_0.7Bi_2.4Ta₂O₉ (SBT) were deposited on the pre-crystallized SBT seed layer with the same composition using sol-gel and spin coating methods. Unseeded and seeded SBT thin films were crystallized to fluorite by heating at 600°C for 1h and they were further heated in the range of 710-740°C at 10°C intervals for different time periods to analyze fluorite-to-Aurivillius phase transformation characteristics. X-ray diffraction (XRD) results on the heated films indicate that the phase transformation kinetics is greatly enhanced in the seeded ones. Quantitative X-ray diffraction (Q-XRD) was performed and the results were used for Johnson-Mehl-Avrami (JMA) isothermal kinetic analyses. From JMA plots Avrami exponent values for unseeded and seeded films were determined as ∼1.5 and ∼1.1, respectively, which implies that each film has a different nucleation mechanism. Using Arrhenius plots the activation energy values for the phase transformation of unseeded and seeded films were determined as ∼263 and ∼183 kJ/mol, respectively. The nucleation mechanism difference and the resultant activation energy difference provide the origin of enhanced kinetics in seeded SBT thin films.