The glass ceramics of various compositions 60SiO2.(40- x)Bi2O3.xFe2O3 with x = 0, 1, 2, 3, 4 and 5 were prepared by annealing the as prepared glasses at temperature ~50oC above the glass transition temperature (Tg), in the electrically heated furnace and then hold the temperature constant for one hour. The ac conductivity of different compositions of iron doped bismuth silicate glass ceramics were studied in the wide temperature range 533 K to 713 K and frequency range 10-1 Hz to 1MHz. The temperature and frequency dependent conductivity was found to obey Jonscher’s power law all the compositions and found to increase with increase in Fe2O3 content. Various parameters like dc conductivity ( dc s ), cross -over frequency ( H w ) and frequency exponent ( s ) were estimated from theoretical fitting of experimental data of ac conductivity with Jonscher’s power law, which showed very good agreement for all the compositions. Enthalpy to dissociate the cations from original site to a charge compensating center (Hf) and enthalpy of migration (Hm) had also been estimated. The conductivity data were analyzed in terms of different theoretical models to determine the possible conduction mechanism. Analysis of the conductivity data and the frequency exponent ‘ s ’ showed that the correlated barrier hopping of electrons between Fe2+ and Fe3+ ions in the glass ceramics was suitable to describe the conduction mechanism for ac conduction. The temperature dependent dc conductivity were analyzed using the theoretical variable range hopping model (VRH) proposed by Mott which describe the hopping conduction in disordered semiconducting glass in low temperature range. The various polaron hopping parameters were also calculated. Greave’s VRH model was found to be in good agreement with experimental data.
