Abstract
The dynamics of Ca 2+ ions and the optical properties of calcium bismuth silicate glasses were investigated using relaxation spectroscopy and optical absorption spectra. These glasses were prepared by normal melt quench technique. Density, molar volume and glass transition temperature (T g) have been measured. A large difference in the values of T g and crystalline temperature (T C) suggests the thermal stability of these glasses. The ac and dc conductivities, activation energy for dc conduction (E dc) and for relaxation frequency (E τ) were extracted from the impedance spectra. The compositional variation in conductivity has been attributed to the presence of mixed glass former effect in these glasses. Both electric modulus and the conductivity formalism have been employed to study the relaxation dynamics of charge carriers in these glasses. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates that the dynamic processes for ions in these glasses are temperature independent. Similar values of E dc and E τ indicate that the ions have to overcome the energy barrier of same height in their conduction as well as relaxation. The observed conductivity spectra follows power law with exponent ‘s’ which increases regularly with frequency and approaches unity at higher frequencies. It has been observed that the position of the absorption edge and cutoff wavelength shift towards blue as Bi 2O 3/SiO 2 ratio decreases. The compositional variation in optical band gap (E g) has been attributed to the influence of the CaO and SiO 2 on conduction band. The values of Urbach energy confirm the existence of phonon-assisted indirect transitions in the present glass system. The average electronic polarizability of oxide ion (α O 2−) and the optical basicity (Λ th) have been estimated from the calculated values of the optical band gap and were found to be dependent directly on Bi 2O 3/SiO 2 ratio.
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