Dual Chemical Role of Ag as an Additive in Chalcogenide Glasses

Ternary (GeₓSe_1-x)_1-yAgy bulk glasses in the Se-rich region (x<1/3) are shown to be intrinsically phase separated into an Ag₂Se-rich glass and a residual GeₜSe_1-t backbone ( $t>x$ at y≠0) with Ag acting as a network modifier. The existence of an Ag₂Se glass with a Tg0ex0ex=0ex0ex230^∘C is explained quantitatively in terms of constraint counting algorithms. In contrast, Ge-rich glasses (x≥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.