Glass transition T_g and thermal expansion in glassy materials measured by time-resolved x-ray diffraction

We have determined changes in thermal expansion coefficient α_th and relaxation behavior of glassy materials by monitoring the first maximum of the diffraction pattern, obtained in transmission during in-situ heating in a high-intensity high-energy monochromatic light beam. The excess quenched-in free-volume ΔV_f and its relaxation kinetics can also be determined. Like metallic glasses, oxide glasses also show the glass transition T_g with excess free-volume trapped during cooling. The results allow quantitative determination of T_g by diffraction that compares well with T_g obtained by calorimetry as was previously reported for metallic glasses and the relaxation of excess free volume.