Abstract
The electrical properties of xCaO–(20 — x)BaO–20Fe2O3–60P2O5 glasses with x = 0, 5, 10, 15 and 20 mol% have been studied in the frequency range 400 Hz–200 kHz and over a temperature range 323–593 K. The ac conductivity as a function of temperature was divided into two domains, one where the absolute magnitude of the ac conductivity was close to the dc conductivity and another where it was larger than the dc conductivity. At the same temperature, the dc conductivity varied only slightly in glasses with different CaO and BaO content. It is concluded that the conductivity in these mixed CaO and BaO iron phosphate glasses is electronic and depends upon the Fe2+/(Fe2+ + Fe3+) ratio. In the high-temperature region above θD/2 (where θD is the Debye temperature) the Mott model of small polaron hopping (SPH) between nearest neighbours is consistent with the conductivity data, while at low temperature (below θD) the Greaves intermediate variable-range hopping (VRH) model is found to be appropriate. The electrical conduction of the glasses is confirmed to be non-adiabatic SPH. Mössbauer spectral analysis indicates the presence of both Fe2+ and Fe3+ ions.
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