Physical, optical and electrical properties of calcium bismuth borate glasses

Abstract

The variation in physical, optical and electrical properties has been investigated as a function of Bi₂O₃ content in 20CaO · xBi₂O₃ · (80 − x)B₂O₃ (0 ≤ x ≤ 60, in mol%) glasses. The samples were prepared by normal melt-quenching process, and the optical absorption and reflection spectra were recorded in the wavelength range of 400–950 nm. The fundamental absorption edge has been identified from the optical absorption spectra. The optical band gap, E _g, for indirect allowed and indirect forbidden transitions has been determined from the available theories and its value lies between 1.80–2.37 eV and 1.08–2.19 eV, respectively. The theoretical fitting of the optical absorption indicates that the present glass system behaves as an indirect gap semiconductor. The origin of the Urbach energy, ΔE, has been associated with the phonon-assisted indirect transitions. The refractive index and optical dielectric constant have been evaluated from the reflection spectra. The density and molar volume are found to depend on the molar concentration of Bi₂O₃. The values of DC electrical conductivity have been measured from 373 to 623 K and the activation energy has been calculated. Theoretical optical basicity has been reported as a function of the Bi₂O₃ content. The variations have been discussed in terms of structural changes.

Keywords:

• Oxide glasses
• Optical properties
• Density
• Indirect semiconductor
• DC conductivity

Acknowledgements

The authors are thankful to UGC and CSIR, New Delhi, for providing financial support.