Redox effects on the structure and properties of Na-Mo-Fe-phosphate glasses

Abstract Na-Mo-Fe-phosphate glasses were prepared with reducing and oxidizing raw materials and the effects of the different Fe2+/Fe3+ and Mo5+/Mo6+ ratios on glass structure and properties were determined. M o ¨ ssbauer spectroscopy confirms significantly greater concentrations of Fe2+ ions in the reduced glasses and distorted Fe3+O4 sites preferred over the Fe3+O6 sites in the oxidized glasses. Raman spectroscopy reveals the presence of isolated Mo6+O6 sites in the oxidized glasses, and highly distorted Mo5+O5 sites in reduced Mo-rich glasses. The presence of specific Fe- and Mo-polyhedra is correlated with the average phosphate anion length, as characterized by high-pressure liquid chromatography. Generally, for the similar compositions, oxidized glasses have greater molar volumes than the reduced glasses, associated with the formation of isolated Mo6+O6 octahedra and the absence of highly crosslinked Mo5+OPO4 units. Tg increases with increasing Fe3+ fractions in the Fe-rich glasses, whereas for the Mo-rich glasses, Tg increases with greater Mo5+ fractions.