Chemical Bonding and the Nature of Glass Structure

The use of fundamental chemical bonding considerations in the determination of the structures and properties of a wide variety of glasses with predominantly covalent bonding is reviewed. Simple considerations based on chemical ordering, coordination numbers and bond energies, can often be used to obtain information concerning the nature of the average local order around any given type of central atom in such an alloy glass. This information enables the explanation and prediction of various physical, chemical and electrical properties. Examples of these procedures are given by examining some chalcogenide glasses of interest due to their reversible threshold switching (Si18Ge7As35Te40) and memory switching (Ge15Te81Sb2S2 and Ge24Te72Sb2S2) properties.