Optical and electrical properties of binary WO3-Pb3O4 glasses

A glass system of the composition xWO(3) + (100 - x)Pb3O4, With x = 5, 10, 20 and 30 mol.% was prepared. The optical absorption, ac and de conductivities are the subject of the present work. The optical absorption indicates that the electronic transition is indirect and is associated with phonon assisted transition. The exponential dependence of the absorption coefficient as a function of the incident photon energy suggests that the Urbach rule is obeyed, and indicates the formation of a band tail. On the other hand, ac conductivity measurements are performed in the frequency range 0.1-100 kHz, and in the temperature range 300-600 K. The results of the electrical conductivity are discussed on the basis of electronic glass conduction models. Correlated narrow-band limit for random sites and single polaron hopping model are found to describe the experimental results effectively. The dielectric constant was correlated to the optical band gap and a satisfactory relation was found. It was also possible to calculate the thermochromic properties from independent ac and de measurements, and it was possible to evaluate the optical gap at 0 K by extrapolation. (C) 1999 Elsevier Science Ltd. All rights reserved.