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

Abstract

Modulated Differential Scanning Calorimetric (MDSC) studies have been performed on Cu_xAs₄₀Se_60-x glasses with x ranging between 0 and 30 at.%. The thermal parameters, namely the glass transition temperature (T_g), the heat capacity (C_ρ) and the jump in heat capacity at the glass transition (Δ C_ρ) 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 T_g, C_ρ and ΔC_ρ. The observed transitions are also understood on the basis of Formal Valence Shell (FVS) model and the classification of strong and fragile liquids.