EFFECT OF SHARP CONCENTRATION GRADIENTS ON THE STABILITY OF A 2-COMPONENT AMORPHOUS LAYER OBTAINED BY SOLID-STATE REACTION

On the basis of thermodynamic argument it is shown that sharp concentration gradients occurring during diffusion mixing facilitate amorphization by solid state reaction by reducing or suppressing the driving force for crystallization. As the concentration gradient diminishes during diffusive layer growth, the driving force for crystallization of compounds is gradually restored and the energy barrier to their nucleation reduced to the classical value. This approach yields a critical concentration gradient and a thermodynamical critical amorphous layer thickness as observed experimentally. The effect of the Gibbs stability function for both amorphous phase and compounds on the critical gradient is analysed and discussed.