reveals that the substitution of alkali metal ions (Li+
) in the glass
matrix leads to an enhanced concentration of non-bridging oxy-
gens, leading to loosening of the glass network. The increase in
Vg reveals that the rigid network structure become more open
when Bi2O3 content is gradually increased from 10 to 40 mol%. In
other words, the larger value of ionic radius and bond length (con-
sidered according to Shannon [14] and Wells [15], respectively) of
Bi2O3 than that of SiO2 resulted in a formation of excess free
volume, which increases the overall volume of these glasses. This
expansion in structure may be attributed to the inability of the
voids of the silicate network to accommodate Bi3+ ions modifiers
without any expansion of the glass matrix. Some authors observed
similar variations for Bi2O3 with other conventional glass formers
such as P2O5 and Ga2O3 etc. [16,17]. Further, Fig. 1 shows a
noticeable departure from linear increase in Dg as well as Vg for
Bi2O3 > 30 mol%. This anomalous change in Dg and Vg suggest that
some structural changes are occurring in these glasses around
x = 30 mol%. Also the higher value of Vg compared to the calculated
crystalline volume, VC indicates the existence of excess structural
reveals that the substitution of alkali metal ions (Li+) in the glassmatrix leads to an enhanced concentration of non-bridging oxy-gens, leading to loosening of the glass network. The increase inVg reveals that the rigid network structure become more openwhen Bi2O3 content is gradually increased from 10 to 40 mol%. Inother words, the larger value of ionic radius and bond length (con-sidered according to Shannon [14] and Wells [15], respectively) ofBi2O3 than that of SiO2 resulted in a formation of excess freevolume, which increases the overall volume of these glasses. Thisexpansion in structure may be attributed to the inability of thevoids of the silicate network to accommodate Bi3+ ions modifierswithout any expansion of the glass matrix. Some authors observedsimilar variations for Bi2O3 with other conventional glass formerssuch as P2O5 and Ga2O3 etc. [16,17]. Further, Fig. 1 shows anoticeable departure from linear increase in Dg as well as Vg forBi2O3 > 30 mol%. This anomalous change in Dg and Vg suggest thatsome structural changes are occurring in these glasses aroundx = 30 mol%. Also the higher value of Vg compared to the calculatedcrystalline volume, VC indicates the existence of excess structural
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