Self-organization in network glasses

The continuous random network model is widely used as a realistic descripti on of the structure of covalent glasses and amorphous solids. We point out that in real glasses and amorphous materials, there are non-random structur al elements that go beyond just simple chemical ordering. We propose that t he network can self-organize at its formation or fictive temperature, and e xamine some of the possible consequences of such self-organization. We find that the absence of small rings can cause the mechanical threshold to chan ge from a second order to a first order transition. We show that if stresse d regions are inhibited in the network, then there are two-phase transition s and an intermediate phase that is rigid but stress-free. This intermediat e phase is bounded by a second order transition on one side and a first ord er transition on the other. Recent experiments in chalcogenide glasses give evidence for this intermediate phase. (C) 2000 Elsevier Science B.V. All r ights reserved.