Temperature-modulated differential scanning calorimetry studies of the structure of bulk and film GexAsyS60 chalcogenide glasses

Abstract

The recent novel temperature-modulated differential scanning calorimetry (TA Instruments MDSCTM) technique has been applied to the measurement of thermal properties of GexAsyS60 chalcogenide glasses in the glass transition region in bulk glasses and in their thin films. The reversing and non-reversing heat flows through the glass transformation region during both heating and cooling schedules were measured and the values of the parameters, Tg, ΔH, Cp and ΔCp, which characterize the thermal events in the glass transition region, were determined. The structurally determined parameters, Tg, ΔH, Cp and ΔCp, reveal significant changes with composition because in the GexAsyS60 glasses the average coordination number, 〈r〉, increases from 2.4 to 2.8 with increasing x from 0 to 40 at% Ge. A maximum in Tg, ΔH and Cp and a minimum in the heat capacity change, ΔCp, at Tg occur near the composition for which x≈30 at% Ge. These extrema which appear in both films and bulk glasses are ascribed to a change in the network function of Ge atoms replacing As atoms in a covalent network. Recent structural models for chalcogenide glasses have been considered to explain the observed thermal properties.