Viscosity of germanium sulfide melts

Viscosities of GexS1-x melts (0.30 less than or equal to x less than or equ al to 0.44) have been measured by penetration viscometry from 10(7) to 10(1 3) Pa s. The temperature dependence of equilibrium viscosities in this rang e can be expressed approximately by a simple Arrhenius equation. Both the h eat capacity change at the glass transition and the activation energy of vi scous flow monotonously increase with germanium content as predicted by the Adam-Gibbs theory. Therefore, the connectivity of the germanium-sulfur net work is reduced due to decreasing concentration of sulfur which causes incr easing fragility of the undercooled liquid. The glass transition temperatur e exhibits a maximum near the GeS2 composition where heteropolar bonds are predominantly formed. (C) 1999 Elsevier Science B.V. All rights reserved.