Characterization and transport properties of semiconducting Fe2O3-Bi2O3-Na2B4O7 glasses

Semiconducting oxide glasses of the system Fe2O3-Bi2O3-Na2B4O7 were prepared by a press-quenching method. Their DC conductivity was measured in the temperature range of 300-473 K. In this temperature range, the DC conductivity increased from 10−9 to 10−5 Scm−1 with increasing Fe2O3 concentration. Bi2O3 acted as a reducing agent for redox reaction during glass synthesis and affected the conductivity. Mössbauer results revealed that the relative fraction of Fe2+ increases with an increasing Fe2O3 concentration. The conduction mechanism was found to obey the non-adiabatic small polaron hopping model, and was mainly due to hopping between Fe-ions in the glasses. The small polaron coupling γp was calculated and found to be in the range of 17.06-26.25. For varying glass compositions, hopping mobility and carrier density were calculated and their values were in the range of 3.66×10−8-8.17×10−5 cm2V−1s−1 and 1.29×1017-5.04×1018 cm−3 at 400 K, respectively.