Influence of Nb2O5 on the structure, optical and electrical properties of alkaline borate glasses

Glasses with composition xNb2O5·(30 − x)MO·70B2O3 [where M = Ca, Sr, Ba] have been prepared by using normal melt-quench technique. The density (D), molar volume (VM), structure, optical and electrical properties have been investigated in order to understand the role of Nb2O5 in these glasses. Values of D and VM increase with increasing concentration of Nb2O5 in these glasses. The increase in VM indicates that the volume of non-bridging oxygens (NBOs) sites produced by the Nb2O5 is greater than that produced by alkaline oxides in present glasses. The results of optical basicity (Λth) show that the ionic character of these glasses is improving with increase in Nb2O5 content. The analysis of IR spectra reveals the presence of NbO4 and NbO6 units. The band gap energy (Eg) of the present glasses is found to decrease with increase in Nb2O5 content. A theoretical approach has been used to calculate the refractive index (nr), molar refraction (Rm) and optical polarizability (α0) for the glass samples having D in between 1 and 3 g cm−3. The conductivity results support the IR analysis and indicate the presence of NbO4 and NbO6 units in these glasses.