Fragility Index variation in (Li$_{2}$O)x(B$_{2}$O$_{3})$100-x melts

We have measured the fragility index (m) of titled melts as a function of Li$_{2}$O content in the 0\textless x\textless 35{\%} range using Modulated DSC. In this approach, one measures the real and imaginary part of the complex specific heat as a function of modulation frequency ($\nu )$, and deduces an activation energy by plotting the log of the enthalpy relaxation time as a function of inverse Temperature obtained at various $\nu $. For pure B$_{2}$O$_{3}$ glass with a T$_{g} \quad =$ 308\textdegree C, we obtain m $=$ 28 (1). With increasing x, m is found to monotonically increase to 38(1) as x increased to 15{\%}, but then to plateau at a value of m $=$ 42(2) in the range 18{\%}\textless x\textless 25{\%}. These values in m are significantly lower than those reported earlier$^{1}$. In particular, the range of x where we observe a plateau in m, authors of ref. 1 observed a linear increase in the 41\textless m\textless 62 range. T$_{g}$ of our glasses are found to be significantly greater than those of ref. 1, suggesting that the lower value of m in our glasses could be a manifestation of the reduced concentration of bonded water. The range of x across which a plateau is observed also happens to coincide where the isostatically rigid Intermediate Phase reported recently$^{2}$. $^{1}$ G.D.Chryssikos et al. JNCS \textbf{196}, 244 (1996). $^{2}$ K. Vignarooban et al. EPL \textbf{108}, 56001 (2014).