Devitrified phases in CuAsSe glasses

Abstract

Thermal crystallisation studies of (Cu₂Se)_x(As₂Se₃)_{1 - x} glasses, where 0.12 =x=0.5 (Cu at% of 5 to 25) is is carried out using a differential scanning calorimeter (DSC). On heating, glasses with 5 and 10at% of Cu show a single glass transition temperature and a single crystallisation temperature with a small shoulder. Glasses with Cu content of 15, 20 and 25at% exhibit the phenomenon of double glass transition and double crystallisation. Isothermal annealing of the glasses at their respective crystallisation temperature(s) results in phase separation. The CuAsSe₂ compound is the primary crystallisation phase in all the glasses. The thermodynmically stable Cu₃AsSe₄ compound is an additional primary crystallisation phase in the glasses with 15, 20 and 25 at% of Cu. The monoclinic As₂Se₃ compound is the secondary crystallisation product in all the glasses investigated. The presence of these crystalline phases in the devitrified glasses is supported by the multiple melting endotherms observed in the DSC thermograms. An attempt is made to correlate the experimental results with the formal valence shell model.