Mössbauer and X-ray photoelectron spectroscopic studies of heat-treated calcium borate glasses containing iron

Abstract

⁵⁷Fe Mössbauer and X-ray photoelectron spectroscopic studies have been carried out on a number of iron-containing calcium borate glasses which show large changes in d.c. conductivity upon annealing. The Mössbauer spectra of the unannealed glass samples are compatible with the presence of predominantly ferric iron in a six-co-ordinate oxygen environment. Upon annealing a partial ordering of the glassy phase is found as indicated by a reduction in the linewidth of the Mössbauer resonances. Longer annealing times lead to the precipitation ofα-Fe₂O₃ clearly identified by the gradual appearance of a six-line magnetically split pattern in the Mössbauer spectra. These changes are qualitatively correlated with changes in d.c. conductivity of the samples. The binding energies and full width at half maxima of representative core levels of each element present show a remarkable consistency for all samples. Moreover the 2p spectra of iron incorporated in the glassy phase are essentially similar to that of the precipitated Fe₂O₃.