Effect of Sulfur Addition on the Redox State of Iron in Iron Phosphate Glasses

摘要

Moessbauer, IR, and electrical conductivity were investigated in iron phosphate glasses, 40Fe_2O_3-60P_2O_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. Moessbauer spectroscopy was used in order to determine the relative fraction of Fe~(2+), i.e. Fe~(2+)/Fe(total), isomer shift (δ), and quadrupole splitting (Δ). Moessbauer results revealed that the relative fraction of Fe~(2+) increases with an increasing sulfur content. Electrical conductivity showed a similar composition dependency as the fraction of Fe~(2+). 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 Fe~(2+) to Fe~(3+). 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.