Spectroscopic study on iron doped silica-bismuthate glasses and glass ceramics

Fourier transform infrared (FTIR) and electron paramagnetic resonance (EPR) spectroscopic data obtained for iron doped silica-bismuthate glasses were used to investigate the changes induced in the local structure of samples as the ratio between Bi2O3 and SiO2 content changes from 3 to 0.66. The environment of constituent cations was investigated both in vitreous and partially crystallized samples of same composition. Progressive substitution of Bi2O3 by SiO2 contributes to the structural relaxation of vitreous network and enhances glass stability. By crystallization heat treatment the structural units appear to be more uniform as it results from the narrowing of corresponding IR bands and EPR lines. FTIR data show that more affected by composition and heat treatment is the environment of bismuth than that of silicon. EPR data indicate an ordering tendency with SiO2 content in glasses, while in vitroceramics the iron environment is much uniform in samples with less SiO2 content, where Bi12SiO20 phase is developed.