Mixed alkali tungsten borate glasses - Optical and structural properties

Glasses with composition xLi(2)O-(30-x)Na2O-10WO(3)-60B(2)O(3) (where x = 0, 5, 10, 15, 20, 25, and 30 mol%) were prepared by the melt quenching technique. Density, refractive index and glass transition temperature varies non-linearly with glass composition indicting the presence of mixed alkali effect. Optical energy band gap for various indirect and direct (allowed and forbidden) transitions were determined using Tauc plots. IR spectral study reveals the existence of BO3 and BO4 groups with W-O-W vibrations in the present glasses. Based on good correlation among refractive index based electronic polarizability of oxide ions, optical basicity and the Yamashita-Kurosawa's interaction parameter, the present Li2O-Na2O-WO3-B2O3 glasses were classified as semi covalent oxides. (C) 2012 Elsevier B. V. All rights reserved.