Dynamics of strong and fragile glass formers: Differences and correlation with low-temperature properties

Low-frequency Raman spectra of strong and fragile glass forming liquids were measured in a wide temperature range. From an analysis of the spectra and literature data it is found that the main difference in the dynamic structure factor is the ratio of vibrational to relaxational contributions: The stronger the glass former the higher this ratio. It is shown that this difference survives even at very low temperatures and determines the low-temperature anomalies of glasses. A possible way how the observed difference influences the fragility of a liquid is discussed.