Structure and properties of GeGaP sulfide glasses

GeGaP sulfide glasses containing 60–90 mol% GeS2, 0–30 mol% Ga2S3 and 0–33.3 mol% P2S5 have been investigated to determine the compositional dependence of physical properties and network structure. The glass transition temperature (Tg) and absorption edge (λ0) decrease and blueshift, respectively, with addition of Ga until Ga ⩾ P, at which point these properties level off. Replacement of P with Ga in these glasses also changes the P speciation, as determined by 31P nuclear magnetic resonance (NMR) measurements. For glasses with P > Ga, the P polyhedra consist mostly of asymmetric S = PS3/2 tetrahedra and trigonal PS3/2 groups. Above the Ga:P ratio of 1:1, P is found almost entirely in symmetric PS4/2 tetrahedra. The trend in P speciation parallels that of the physical properties of these glasses, providing a structural explanation for compositional variations in Tg and λ0.