Modulated-temperature differential scanning calorimetry and Raman spectroscopy studies of AsxSi100-x glasses

Thermal properties of chalcogenide AsxS100-x glasses in the glass transitio n region have been studied by modulated-temperature differential scanning c alorimetry (MTDSC). All samples in this work were given the same thermal hi story by heating to a temperature above the glass transition, equilibrating and then cooling at a rate of 5 degrees C/min to a temperature of 20 degre es C. The reversing and non-reversing heat flows through the glass transfor mation region during both heating and cooling schedules were measured and t he values of the parameters T-g, Delta H, C-p and Delta C-p, which characte rize the thermal events in the glass transition region, were determined as a function of the glass composition. The structurally determined parameters T-g, Delta H, C-p and Delta C-p reveal major extrema when the composition of AsxS100-x glass becomes As40S60, that is the same as the composition of the corresponding stoichiometric compound. In addition, we observe "small t hresholds" in these properties at 28.5 at % As (As28.5S71.5) around the sam e composition as that reported in the As-Se glasses. No such thermal analys is had been done on the AsxS100-x glasses previously. It is shown that AsxS 100-x glasses where x < 25 at % As are formed from two glass phases. From M TDSC measurements, it was possible to establish the probable composition of the high temperature glass phase and from Raman spectroscopy it was possib le to correlate the MTDSC results with the structure of the As-S glasses. ( C) 1998 Kluwer Academic Publishers.