Mossbauer and IR investigations of iron ultraphosphate glasses

The structures of xFeO (.) (1-x)P2O5 glasses (0 less than or equal to x less than or equal to 0.50) prepared in sealed silica ampoules have been investigated using Mossbauer and infrared (IR) spectroscopies. Mossbauer results indicate that the glasses contain 6-18% Fe(III). Both Fe(II) and Fe(III) ions occupy octahedral coordination environments in these glasses. Analysis of the IR spectra indicates that the structure of glass transforms systematically from a three-dimensional P2O5 network (dominated by Q(3) tetrahedra) to a two-dimensional network (dominated by Q(2) units) as the FeO content increases. This transformation is evidenced by the replacement of the IR band at 1380 cm(-1) attributed to P=O vibrations on isolated Q(3) sites with the band at 1260 cm(-1) band which is attributed to asymmetric vibrations of PO2 groups on the Q(2) tetrahedra. In addition, a new IR band at 1317 cm(-1) is created when FeO is added to P2O5 and this band is assigned to P=O bonds that participate in the coordination environments of the Fe-octahedra. At x similar to 0.35 FeO, the P=O bonds that remain are only those that coordinate with the Fe-octahedra. These structural changes are similar to those observed for other ultraphosphate glasses. (C) 2003 Elsevier B.V. All rights reserved.