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

Abstract 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.