Effect of Bi 2O 3 content on the optical band gap, density and electrical conductivity of MO·Bi 2O 3·B 2O 3 (M = Ba, Sr) glasses

Abstract

Glasses with compositions 20MO· xBi 2O 3·(80− x)B 2O 3 (M = Ba, Sr) with 10 ≤ x ≤ 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 Bi 2O 3 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 Bi 2O 3 content have been discussed in terms of changes in the glass structure. Values of the theoretical optical basicity are also reported.