Abstract
Mossbauer, IR, and electrical conductivity were investigated in iron phosphate glasses, 40Fe(2)O(3)-60P(2)O(5) (in mol%), containing sulfur ranging from 0 to 2, 4, 6, and 8 mass%. Sulfur proved to act as a reducing agent for the redox reaction during the glass preparation. Mossbauer spectroscopy was used in order to determine the relative fraction of Fe2+, i.e. Fe2+/Fe(total), isomer shift (delta), and quadrupole splitting (Delta). Mossbauer results revealed that the relative fraction of Fe2+ increases with an increasing sulfur content. Electrical conductivity showed a similar composition dependency as the fraction of Fe2+. These results indicate that higher electrical conductivity of sulfur-containing iron phosphate glasses is due to small polaron hopping (SPH) between iron atoms of different valance states, i.e., a step-by-step electron hopping from Fe2+ to Fe3+. IR spectra of these glasses are very similar to those of sulfur-free iron phosphate glasses, proving that the structure of sulfur-containing iron phosphate glasses is essentially the same as that of sulfur-free phosphate glasses.