A study of the devitrification of Pd₈₂Si₁₈ over a wide temperature range

Measurements of the crystallization kinetics of amorphous Pd₈₂Si₁₈ with electrical resistivity and differential scanning calorimetry have been made in the temperature range 548-691K. The crystallization has been shown to occur simultaneously from the sample surface and on pre-existing nuclei in the bulk. A numerical model has been developed to simulate the growth kinetics associated with this morphology, and values for the growth velocity, and numbers of surface and volume nuclei have been obtained. It is demonstrated that failure to account properly for the morphology of the growth leads to a nonlinear artifact in the Johnson-Mehl-Avrami analysis of the kinetics. Assuming an Arrhenius temperature dependence for the growth velocity, a decreasing activation energy with decreasing temperature is found; this is in agreement with recent results for isoconfigurational atomic transport in the same system. Auger measurements indicate that silicon segregates to the surface of the sample and oxidizes to form SiO₂, leaving behind elemental palladium.