Structure and properties of GeGaP sulfide glasses

Abstract GeGaP sulfide glasses containing 60–90 mol% GeS 2 , 0–30 mol% Ga 2 S 3 and 0–33.3 mol% P 2 S 5 have been investigated to determine the compositional dependence of physical properties and network structure. The glass transition temperature ( T g ) and absorption edge ( λ 0 ) 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 31 P nuclear magnetic resonance (NMR) measurements. For glasses with P > Ga, the P polyhedra consist mostly of asymmetric S = PS 3/2 tetrahedra and trigonal PS 3/2 groups. Above the Ga:P ratio of 1:1, P is found almost entirely in symmetric PS 4/2 tetrahedra. The trend in P speciation parallels that of the physical properties of these glasses, providing a structural explanation for compositional variations in T g and λ 0 .