FTIR and Mössbauer spectroscopic study of sodium–aluminum–iron phosphate glassy materials for high level waste immobilization

Abstract Complex sodium-aluminum-iron phosphate glassy materials with various Al 2 O 3 to Fe 2 O 3 ratio containing high level waste (HLW) surrogate were characterized by X-ray diffraction and scanning electron microscopy and studied in details by Fourier transform infrared (FTIR) spectroscopy. The samples with high Al 2 O 3 content and not containing Fe 2 O 3 were predominantly amorphous but subjected to devitrification under annealing. Addition of B 2 O 3 and partial Fe 2 O 3 substitution for Al 2 O 3 in the materials increases their resistance to devitrification whereas further substitution and NiO incorporation significantly increase the tendency to devitrification. FTIR spectra demonstrate changes in the structure of glassy materials caused by both structural variations in the anionic motif and occurrence of crystalline phases in the materials. According to Mossbauer spectroscopy data, iron in the glassy samples is present as octahedrally coordinated Fe 3+ ions while in the partly devitrified samples iron is partitioned among vitreous and crystalline phases entering the vitreous phase mainly as Fe 3+ O 6 units and crystalline phases as major Fe 3+ and minor Fe 2+ ions in a magnetically ordered state and participating in a “fast” electronic exchange.