Raman studies and some physical properties of selected (PbO)x(Nb2O5)y(TeO2)1−x−y glasses

Selected Nb2O5-TeO2, PbO-Nb2O5-TeO2 and PbO-TeO2 glasses were prepared from very pure oxides. The glass-transition temperature increased from 281 to 411 °C with an increase in Nb2O5 content and, simultaneously, the coefficient of thermal expansion decreased from 21 to 11 ppm/°C. Raman scattering measurements indicated that TeO4 trigonal bipyramids, TeO3+1, TeO3 trigonal unit and NbO6 octahedra were the basic structural units of Nb2O5-TeO2 and PbO-Nb2O5-TeO2 glasses. The optical band gap was determined in the region 3.39-3.60 eV and the coefficient of the temperature dependence of the optical gap for the temperatures between 30 and 250 °C in the region 4.1 × 10−4-6.8 × 10−4 eV/K was found. Non-linear refractive index of the studied glasses was estimated from the optical gap values at around 0.85 × 10−11 esu.