Oxygen and Phosphorus Coordination Around Iron in Crystalline Ferric Ferrous Pyrophosphate and Iron-phosphate Glasses with UO₂ or Na₂O
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Fe K-edge x-ray absorption fine-structure (XAFS) measurements were performed on glass samples of (Fe3O4)0.3(P2O5)0.7 with various amounts of Na2O or UO2. Near-edge and extended-XAFS regions are studied and comparisons are made to several reference compounds. We find that iron in the base glass is ~25% divalent and that the Fe2+ coordination is predominantly octahedral, while Fe3+ sites are roughly split between tetrahedral and octahedral coordinations. Also, we measure roughly one FeñOñP link per iron. Substitution of Na2O or UO2 up to 15 mo1% primarily affects the first FeñO shell. The results are compared to data from the related material Fe3(P2O7)2.