Abstract
Dynamic light scattering was performed to measure the structural relaxation in sodium and zinc phosphate glass-forming melts in the range from 50 mol% to 40 mol% P2O5 where long polymer-like chains of PO4 tetrahedra are systematically shortened in length. The findings reveal compositional changes in the non-exponentiality of the relaxation as well as in the glass fragility, the latter of which exhibits anomalous differences between sodium and zinc.