Effect of Bi2O3 content on the optical band gap, density and electrical conductivity of MO.Bi2O3.B2O3 (M = Ba, Sr) glasses

Glasses with compositions 20MO(.)xBi(2)O(3)(.)(80-x)B2O3 (M = Ba, Sr) with 10 less than or equal to x less than or equal to 60 (in mol%) have been prepared using the normal melt-quench technique. The optical absorption spectra of the glasses have been recorded in the wavelength range 400-700 nm. The fundamental absorption edge has been identified from the optical absorption spectra. The values of optical band gap for indirect allowed and indirect forbidden transitions have been determined using available theories. The origin of the Urbach energy is associated with the phonon-assisted indirect transitions. The density and molar volume studies indicate that Bi2O3 in these glasses is acting partly as network modifier and partly as network former. Values of the direct-current electrical conductivity have been measured from 373 to 623 K and the activation energy has been calculated. The variations in optical band gap, density and electrical conductivity with Bi2O3 content have been discussed in terms of changes in the glass structure. Values of the theoretical optical basicity are also reported. (C) 2004 Elsevier B.V. All rights reserved.