Oxide glass structure: Towards a working hypothesis for the 21st century
Adrian C Wright
J.J. Thomson Physical Laboratory, University of Reading, RG6 6AF, U.K.
During the 20th Century there were three major theories of the structure of oxide glasses, viz. the Early Crystallite Theory (discrete crystallites separated by some form of “grain boundary”), the Random Network Theory (continuous statistically-disordered network) and the Cybotactic Theory (continuous network with spatial fluctuations in the degree of order). The problem is that NOT ONE of these theories can be eliminated, as a result of X-ray or neutron diffraction studies, nor on the basis of small-Q scattering (SAXS or SANS) data. Thus an alternative (thermodynamic) approach is required, and it will be demonstrated that two of these three theories have problems in explaining the chemical nanoheterogeneity of glasses having more than one component, the process of devitrification/crystallisation (especially that of nucleation), and/or cationic conduction in glasses containing network-modifiers, thus leading to a possible working hypothesis for the 21st Century.