Chemical ordering and fragility minimum in Cu–As–Se glasses

Modulated Differential Scanning Calorimetric (MDSC) studies have been performed on CuxAs40Se60−x glasses with x ranging between 0 and 30 at.%. The thermal parameters, namely the glass transition temperature (Tg), the heat capacity (Cp) and the jump in heat capacity at the glass transition (ΔCp) are measured. The composition dependence of these thermal parameters has been found to exhibit interesting variations particularly at x = 20. Thermal crystallization studies show that the structural network is mainly characterized by the ternary Cu3AsSe4 units with As2Se3 and Cu2As3 units depending on the concentration of Cu. These structural differences arising as a function of composition are reflected in the Tg, Cp and ΔCp. The observed transitions are also understood on the basis of Formal Valence Shell (FVS) model and the classification of strong and fragile liquids.