Dual chemical role of Ag as an additive in chalcogenide glasses

Ternary (GexSe1-x)(1-y)Ag-y bulk glasses in the Se-rich region (x < 1/3) are shown to be intrinsically phase separated into an Ag2Se-rich grass and a residual GetSe1-t backbone (t > x at y not equal 0) with Ag acting as a network modifier. The existence of an Ag2Se glass with a T-g = 230 degrees C is explained quantitatively in terms of constraint counting algorithms. In contrast, Ge-rich glasses (x greater than or equal to 2/5) are homogeneous, wherein Ag acts as a network former, replacing available Ge sites of the backbone to be 3-fold coordinated to Se.