Oxygen and phosphorus coordination around iron in crystalline ferric ferrous pyrophosphate and iron-phosphate glasses with UO_2 or Na_2O

摘要

Fe K-edge x-ray absorption fine-structure (XAFS) measurements were performed on glass samples of (Fe_3O_4)_o.3(P_2O_5)_o.7 with various amounts of Na_2O or UO_2. 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 Fe~2+ coordination is predominantly octahedral, while Fe~3+ sites are roughly split between tetrahedral and octahedral coordinations. Also, we measure roughly one Fe-O-P link per iron. Substitution of Na_2O or UO_2 up to l5 mol primarily affects the first Fe-O shell. The results are compared to data from the related material Fe_3(P_2O_7)_2.