Configurationally frozen defects, random strains and landau theory of crystal to glass transition

A Landau theory is proposed to describe the crystal to glass transition in systems under strict polymorphic constraint, or constant chemical affinity. Under such a kinetic constraint, long-range diffusion is absent in the metastable systems and thus large scale atomic configuration rearrangements are prohibited. But local short-range relaxation of atoms from unfavorable positions is possible. The resulting static atomic displacement fields can therefore be used as the primary order parameter in the Landau theory to describe the crystal to glass transition. The presence of static defects, especially topological defects, generated from different sources during amorphization introduces random static strain fields that affect the transition critically by coupling to the primary order parameter. Depending on the kinetic constraint and certain material properties, the random strain fields associated with these 'frozen-in' defects can lead to smearing-out effects on the ordinary first-order polymorphic melting transition; when the random strain fluctuation becomes anomalously large, the transition can be smeared out completely, making the crystal to glass transition appear continuous. Some thermodynamic properties and the metastable phase diagram of a model system of binary solid solution are discussed in the context of the Landau theory.