Role of Iron in Calcium Phosphate Glasses

Some physical properties okf phosphate glasses con-taining up to about 26 mol% Fe₂O₂ were studied. Pronounced changes in properties were observed at compositions containingabout 6, 10, and 13 mol% Fe₂O₃. The X-ray diffraction spectra of devitrified (heat-treated) samples showed new compounds near these compositions. Electron spin resonance and optical studies confirmed the presence of Fe³⁺ and Fe²⁺ in both 4- and 6-coordination. An increase in total iron in these samples was associated with a decrease in the ratios Fe²⁺ 4-coordinated/Fe³⁺ 6-coordinated 6-coordinated and Fe³⁺ 4-coordinated/Fe³⁺ 6-coordinated up to about 2.0 mol% Fe₂O₃, as shown by the intensity of the optical absorption bands at about 2.0 and 1.0 μm and by the intensity of the ESR lines at g⋍4.2 and 2.0, respectively. Samples containing up to 4.3 mol% Fe₂O₃ showed an increase in Fe³⁺ concentration and a decrease in Fe²⁺ concentration after gamma irradiation. The electrical conductivity and activation energy decreased sharply with increasing Fe₂O₃ content.