The P-O bond lengths in vitreous P2O5 probed by neutron diffraction with high real-space resolution

Neutron diffraction has been used to determine the two P-O bond lengths which occur in the threefold-linked tetrahedral PO4 structural units of vitreous P2O5. The large maximum momentum transfer (Q(max) approximate to 500 nm(-1)) which is available on the LAD instrument at the ISIS spallation neutron source gives high real-space resolution which enables a clear separation to be made between P-O bond lengths involving terminal oxygens (143.2 +/- 0.5 pm) and those involving bridging oxygens (158.1 +/- 0.3 pm). The two P-O distances in vitreous P2O5 were found to have narrower distributions than have previously been observed, using the same experimental conditions, for any other modified phosphate glass.