Linking the ring-morphology of (Li2O)x(B2O3)100-x and (Na2O)x(B2O3)100-x borate glasses with topological phases and melt dynamics

Abstract

Raman scattering and calorimetric measurements on lithium borate, (Li₂O)_x(B₂O₃)_100-x, and sodium borate, (Na₂O)_x(B₂O₃)_100-x, glasses, 0 < x < 45 %, were undertaken to elucidate the role of glass molecular structure on the topological phases and melt dynamics. For (Na₂O)_x(B₂O₃)_100-x glasses, a wide square-well like variation of the enthalpy of relaxation at the glass transition was observed, showing an intermediate phase (IP) in the 20 % < x < 40 % range of soda. Raman results reveal the IP to be correlated with the existence of six unique Isostatically Rigid Local Structures (ISRLSs) which have characteristic ring morphologies appearing sequentially with increasing soda concentration across the IP. Additionally, several narrowly defined Gaussian-like fragility index, m, minima are observed to manifest in the 15 < m < 20 range, which appear sequentially with increasing mol x% and directly correspond to the stoichiometry of the six molecular ring based ISRLS. Parallel results are observed for (Li₂O)_x(B₂O₃)_100-x.