Polaronic transport in iron phosphate glasses containing HfO₂ and CeO₂

Abstract

The electrical and dielectric properties of three series of glasses, xHfO-(40 - x)FeO-60PO, 0 ≤ x ≤ 8 mol%, xCeO-(40 - x)FeO-60PO, 0 ≤ x ≤ 8 mol%, and xHfO-(38 - x)FeO-2BO-60PO 2 ≤ x ≤ 6 mol%, have been investigated by impedance spectroscopy over a wide frequency and temperature range. As expected, these glasses exhibit polaronic conductivity which strongly depends on the fraction of ferrous ions, Fe/Fe. Following a detailed discussion on the DC conductivity, we use the MIGRATION concept to model their conductivity spectra. It is found that in each series of glasses, the shape of the conductivity isotherms remains the same indicating that the time-temperature superposition principle is satisfied and that the mechanism of conductivity is the same. Returning to a model-free scaling procedure, namely Summerfield scaling, it is found that while conductivity isotherms for each composition yield a master curve, we need to suitably shift individual master curves on the frequency axis to generate a super-master curve. We examine the dependence of the DC conductivity and the shift factors on the number density of charge carriers. Next, using the fact that the dielectric strength of relaxation for each isotherm is well-defined in these systems, we scale the conductivity isotherms using the Sidebottom scaling procedure. This procedure yields a super-master curve, implying that length scales for polaronic transport also change with composition. Further, using the scaling features of permittivity spectra, we extract in a straightforward way the characteristic spatial extent of localized hopping of polarons and find that it decreases with increasing number density of charge carriers. The magnitude of these values obtained from permittivity spectra lies in the same range as those for the polaron radius calculated using the equation proposed by Bogomolov and Mirilin.

Polaronic Conductivity in Iron Phosphate Glasses Containing B2O3

“…Observed trends suggest that the dominant parameter for the polaronic transport in these glasses is Fe 2 O 3 content and not the addition of B 2 O 3 . Interestingly, the DC conductivity of binary 40Fe 2 O 3 -60P 2 O 5 mol.% glass without B 2 O 3 which we previously reported [30] lies precisely on the linear dependence of DC conductivity versus Fe 2 O 3 content of the present glass system, see the black symbol in Figure 2c. This further supports our conclusion that the polaronic transport in these glasses is controlled solely by the iron oxide content and hence, polaron number density.…”

“…Here, it should be noted that the polaron number density depends not only on the total amount of Fe 2 O 3, but also on the fraction of Fe 2+ and Fe 3+ ions. For the Fe 2+ /Fe tot ratio ≤ 0.5 the polaron number density is determined by the product of number density of the total iron ions and fraction of ferrous ions, whereas for Fe 2+ /Fe tot ratio > 0.5 it is determined as a product of the number density of the total iron ions and the fraction of ferric ions [3,4,30]. In the previous structural study of this glass system [24], it was shown that there is no significant variation in Fe 2+ /Fe tot ratio since the fraction of ferrous ions for selected glasses changes from 0.16 to 0.22.…”

Nature of mixed electrical transport in Ag2O–ZnO–P2O5 glasses containing WO3 and MoO3

“…The dispersive behavior is more visible at lower frequencies and temperatures, and shifts to higher frequencies at higher temperatures. In general, conductivity dispersion is characteristic for ionic as well as polaronic glasses [53] and, hence, it is not connected to the type of charge carriers. Instead, it is closely related to the structural disorder, one property which is common to all glasses.…”

Study of Electrical Transport of Ag2O – CdO – MoO3 Glass‐Nanocomposite‐Semiconductor

“…The dc conductivity for all the glass‐nanocomposites under investigation is shown in Figure as a function of reciprocal temperature. Smooth variation of the dc conductivity with temperature is the characteristic of semiconducting behavior of the samples of small polaron hopping conduction . However, in the high and low temperatures, the activation energies (Table ) were computed from the slope of the graphs in the two range of temperature.…”