A generalized theory of compositional changes and structural relaxation in amorphous materials

Abstract

A generalized theory of concurrent compositional changes and structural relaxation has been developed by combining the classical internal parameter description of the glassy state and the square gradient thermodynamics of inhomogeneous systems. The new formulation provides a rational basis to analyze coupling effects between compositional and structural changes. This coupling results from the equilibrium between local composition and local structure. The new formalism generalizes previous results about the strain energy effects in phase separation. It shows that irrespective of the physical nature of the internal parameters, the binodal and spinodal boundaries are always suppressed. Furthermore the new theory predicts some general results regarding the kinetics of compositional changes. For example the process of homogenization in single phase region is accelerated in the quenched state. On the other hand, the kinetics of spinodal decomposition in the immiscibility region is retarded in the quenched state (compared to that in the annealed state). Several other consequences pertaining to spinodal decomposition, nucleation and structural relaxation are discussed.