Polaronic Conductivity in Iron Phosphate Glasses Containing B₂O₃

We report on the electrical properties of glasses with nominal composition xB₂O₃-(100-x)[40Fe₂O₃-60P₂O₅],x = 2-20, mol.%. The conduction transport in these glasses is polaronic and shows a strong dependence on Fe₂O₃ content and polaron number density. The changes in DC conductivity are found not to be directly related to B₂O₃, however structural changes induced by its addition impact frequency-dependent conductivity. All glasses obey Summerfield and Sidebottom procedures of scaling conductivity spectra indicating that the polaronic mechanism does not change with temperature. An attempt to produce a super-master curve revealed that shape of the conductivity dispersion is the same for glasses with up to 15.0 mol.% B₂O₃ but differs for glass with the highest B₂O₃ content. This result could be related to the presence of borate units in the glass network. Moreover, the spatial extent of localized polaron motions increases with the decrease of polaron number density, however, this increase shows a larger slope than for previously reported iron phosphate glasses most probably due to the influence of B₂O₃ on glass structure and formation of polarons. While Summerfield scaling procedure fails, Sidebottom scaling yields a super-master curve, which indicates that polaronic hopping lengths also change with changing polaron number density in these glasses.