Medium-range order and random networks

Micro-crystallite and continuous random network (CRN) models started life i n the same decade. Their fates have been quite different. With the discover y of each new family of glasses, micro-crystallite models have been tested in extreme versions and, rightly, found to be inadequate. CRN models have b een treated much more elastically, with modifications inserted to accommoda te new experimental facts. It is now hard to find a clear statement of what the term CRN means, and most definitions are system-specific. An attempt i s made here to present a view of the structure of network glasses, which re cognises the strengths and weaknesses of ordered and random models. and the impact of recent experimental investigations of medium-range structure. (C ) 2001 Elsevier Science B.V. All rights reserved.