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Abstract
Lead metaphosphate glass is characteristically prone to aqueous attack but becomes chemically resistant on the addition of iron oxide. We have measured the K-edge extended X-ray absorption fine structure (EXAFS) of Fe and the LIII-edge EXAFS of Pb and find the atomic environments of the two sites to be very different. Whereas Fe is octahedrally coordinated with an oxygen distancce of 1•9(5) Å, the coordination of Pb is 8 (±1) and the sites display considerable disorder with an average lead—oxygen distance of 2•4(7) Å. X-ray absorption near-edge structure (XANES) measurements of the P K-edge confirm the presence of phosphate as (PO4)n, chains. These results suggest that, by pinning the structure, Fe sites not only shorten the average polyphosphate chain length but also block the percolation of Pb ions. Both effects increase the chemical resistance of the structure to aqueous attack and also reduce the tendency of these glasses to crystallize.