Evolution of Local Structures in Alkali-Borate Glasses

Abstract

We analyze the dependence of relative proportion of various characteristic clusters in binary alcali-borate glasses on modifier's concentration $x$. A pure $B_2O_3$ glass contains a huge amount of boroxol rings and some amount of boron atoms in between, linking the boroxol rings via oxygen bonds. The addition of the $Na_2O$ modifier creates four-coordinated borons, but the resulting network glass remains totally connected. We study local transformations that lead to creation of new configurations like tetraborates, pentaborates, diborates, etc., and set forth a non-linear differential system similar to the Lotka-Volterra model. The resulting density curves of various local confugurations as functions of $x$ are obtained. Then the average rigidity is evaluated, enabling us to compute the glass transition temperature $T_g(x)$ for a given value of $x$