Abstract
Photon correlation spectroscopy was used to investigate the primary viscous relaxation in mixed network former glasses in which polymeric sodium metaphosphate is crosslinked by the addition of a second network forming oxide (GeO
, B
O
, Bi
O
, Ga
O
or TeO
). Analysis of the relaxation provides both the glass transition temperature and fragility as a function of mixing. In each system, a companion nuclear magnetic resonance study exists in the literature which provides valuable insight into the complex bond structure of the oxide network. We demonstrate the glass transition temperature is proportional to the average bridging oxygen bond density while the fragility is not. Instead, a topological correction of the bond density, invoked when rigid super-structural network forming units are present, results in a more satisfactory dependence of fragility on the bond structure of the network.