Thermophotometric study of phase transformations in silver-zinc alloy thin films

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Abstract
The transformations between β1, ζ, and β phases in a sputter-deposited Ag-50 at. % Zn alloy thin film were examined by a developed thermophotometric apparatus. Good observations were made using the change in reflectivity of the thin film with temperature and time, and some characteristic transformation behaviors in the thin film were made clear. Kinetics of the β1→ζ transformation were analyzed using the Johnson–Mehl–Avrami equation. The activation energy obtained from the relaxation time measured at different temperatures was 220.6 kJ/mol. It was much larger than that in the bulk. The time exponent of the equation was 1.51. This shows that the ζ phase nucleates at the grain edge and/or the boundary of the β1 phase after site saturation under a zero nucleation rate. The activation entropy was a large positive value, and the transformation interface was expected to have a complicated structure.