On a model structure for amorphous solids: A working approach to the structure of a perfect amorphous solid

Abstract

According to the arguments by Sadoc a model structure for amorphous solids is defined, on the basis of the dense random packing (DRP) model, as a tetrahedral packing of hard spheres in a curved non-Euclidean space followed by a mapping onto the linear Euclidean space. The mapping introduces an equivocalness into the topology of the DRP, of which the nature is the central problem for the description of the model structure. The energetic implication of the DRP is given by a nil excess entropy. This definition of the DRP as a model structure for amorphous solids can be verified through the observation of densities, density fluctuations, mean coordination numbers, excess entropies, etc. Structural and thermodynamical changes of metallic glasses due to particle bombardments and cold works are compiled, and are reasonably interpreted with a reference to the DRP as defined above, suggesting the adoption of the DRP as a model structure for amorphous solids with single kinds of atoms. The model is extended to systems of different kinds of atoms with chemical orders. The extension is feasible by defining the structure units, which materialize the chemical order, and which are arranged as topologically equivalent to the hard spheres in the DRP. The arguments are verified by the effects of neutron irradiation on silica glass. The model structure here defined proves to work as a reference when an amorphous material is to be characterized, just as does the model of a perfect crystal for the characterization of crystalline materials.