Spectroscopic investigation of MoO3-Fe2O3-P2O5 and SrO-Fe2O3-P2O5 glasses.: Part I

The relationship between the composition, structure and selected properties for four series of iron phosphate glasses containing MoO3 and SrO has been investigated. The three series of MoO3-Fe2O3-P2O5 glasses were prepared with increasing MoO3 content. In series A the molar Fe/P ratio was constant at 0.67, in series B the O/P ratio was 3.5, whereas, in series C the molar percentages of Fe2O3 was fixed at 40 mol%. In the fourth series, M, SrO was added to maintain the Fe/P ratio constant at 0.67. The structural changes in these glasses have been studied by Raman spectroscopy. The Raman spectra show that MoO3 is incorporated into the phosphate network. However, the structure/ properties are strongly influenced by the overall O/P ratio. In glasses with O/P > 3.5 the addition of MoO3 depolymerized some of the bridging oxygens in pyrophosphate units to form isolated (PO4)(3-) orthophosphate groups. The decrease in glass temperature, T-g, and glass density, D, increase in thermal expansion coefficient, alpha, and glass density, D, for these glasses are attributed to an increase in the number of weaker P-O-Mo bonds connected to both orthophosphate and pyrophosphate units. The replacement of the stronger P-O-P bonds for the weaker Mo-O-P bonds imparts greater covalency to the network and contributes to the lower bond strength as the bond covalence decreases from P-O to Mo-O. The addition of up to 20 mol% SrO does not produce any changes in the Raman spectra and any further disruption of pyrophosphate chains. (C) 2003 Elsevier B.V. All rights reserved.