Structural fluctuations in glass-forming liquids: Mössbauer spectroscopy on iron in glycerol

Mössbauer absorption spectra of Fe2+57 dissolved in a glycerol-water mixture have been measured over a wide temperature range (80"275 K). In the supercooled liquid state the shapes of the spectra depend strongly on temperature. The Mössbauer spectra can be fit with jump diffusion with a Cole-Davidson distribution of fluctuation times. The results are in agreement with those obtained from dielectric and ultrasonic volume relaxations, proving that the relaxation of viscous liquids is responsible for the line broadening of the spectra. From the temperature dependence of the integrated area of the Mössbauer spectrum a second dynamic process is inferred. Its activation energy of 31.4 kJ/mol is typical for the relaxation.