Influence of the heat treatment on the Mössbauer spectrum of a simulated nuclear-waste glass

The crystallization behaviour of a reference glass for the conditioning of α-contaminated waste is studied by means of ⁵⁷Fe Mössbauer spectroscopy at 80 K and at room temperature. The parent glass and three, nearly fully crystallized samples, produced by heating at 620, 700 and 800°C respectively, the latter temperature being above the glass' crystallization temperature T_c, have been considered. All spectra have been analysed by both a superposition of two ferrous and two ferric doublets and by a superposition of a ferrous and a ferric quadrupole splitting distribution. It is concluded that the latter method is to be preferred for the spectra of those samples which have not been heated above T_c. The change in the crystallites' morphology of the glass samples as a function of the heat-treatment temperature, i.e. from nearly equiaxed crystallites at 620°C to plate-like ones at 700°C seems to have no significant effect on the Mössbauer parameters. For al spectra, a linear correlation between quadrupole splitting and isomer shift is derived. The results are discussed in terms of different iron coordinations and geometrical deformations thereof.