Résumé
The explanation of the physical and chemical properties of amorphous materials requires knowledge of their composition, thermodynamic history, and structure. Whereas, for example, only structural units in the first coordination sphere contribute to some optical properties, mechanical, electrical, or thermal properties are influenced by the arrangement and the connections of these structural units [3.1]. For crystalline solids whose structure is predominantly determined by the unit cells containing only a few atoms and by symmetry operations, a distinct description of the structure is possible. Amorphous solids such as glasses per definition have a non-periodic structure. But this does not mean that the sites are randomly distributed in a statistical way, only that there is a lack of translational periodicity. Actually, the structural units of amorphous systems and crystals with the same composition are often identical in the first coordination sphere (short-range order SRO) but, unfortunately, the polymerization of the network (long-range order LRO, which per definition is without any information about order so that the lower distance limit depends on the structure evaluation of measurements with different methods) of amorphous systems is not identified. It is therefore difficult to find simple operations for the description of the structure of amorphous solids and, consequently, difficult to detect the correlation between structure and properties.