Role of Iron and Electrical Conductivity in Iron Calcium Phosphate Glasses
Mossbauer spectroscopy, X-ray diffraction and magnetic susceptibility techniques were used to study the role of iron in calcium phosphate glasses before and after heat treatment. Factors affecting the electrical conductivity of these glasses included the total iron concentration, ferrous-ferric ratio, devitrification by heat treatment, and the type of local order in the glass. An exponential decrease in log ρ was observed with increasing total iron concentration from about 8 to 17 wt. % Fe2O3. The range at which there is a change in slope of the exponential (about 11–13 wt. % Fe203) is characterized by the presence of a new compound (FePO4) in the heat treated samples, as confirmed by X-ray diffraction studies. These samples, heated for 88 hours at 750°C, showed a minimum resistivity. The foregoing observations support the postulate that local order in the glasses of this series is similar to that in corresponding crystals separated on devitrification of these glasses by heat treatment. The appearance or disappearance of these crystals (eg. FePO4) at certain compositions was found to coincide with changes in physical properties such as conductivity.
KeywordsHeat Treatment Mossbauer Spectroscopy Isomer Shift Phosphate Glass Heat Treated Sample
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