Oxygen and phosphorus coordination around iron in crystalline ferric ferrous pyrophosphate and iron-phosphate glasses with UO₂ or Na₂O

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 Fe–O–P link per iron. Substitution of Na₂O or UO₂ up to 15 mol% primarily affects the first Fe–O shell. The results are compared to data from the related material Fe₃(P₂O₇)₂.