Optical and dielectric properties of the SiO2-B2O3-Bi2O3-TeO2 glass system

Glasses having a composition (45-x)SiO2 center dot xB(2)O(3)center dot 50Bi(2)O(3)center dot 5TeO(2), (where x=15, 20, 25, 30) were prepared by the conventional melt quench technique. An analysis of the absorption measurement has been carried to obtain the optical energy gap and determine the mechanism of transition involved. It was found by increasing B2O3 content that the values of optical energy gap decrease and the refractive index increase. Conduction and relaxation mechanisms in all the investigated glass samples were studied in the frequency range from 45 Hz to 3000 kHz and in the temperature range from 303 to 483 K. The ac and dc conductivities, the activation energy for dc conduction E-dc and relaxation energy E-tau were calculated. Both of E-dc and E-tau values decrease with increasing B2O3 content. The power exponent has been found to be temperature and composition dependent. The decrease in value of the power exponent with an increase in temperature further suggested that the ac conduction mechanism of the studied samples follows the correlated barrier hopping (CBH) model. Similar values of E-dc and E-tau for each glass composition indicated that that the same type of charge barriers are involved in the relaxation and conduction mechanisms.