Viscosity of germanium sulfide melts

摘要

Viscosities of Ge_xS_(1-x) melts (0.30<=x<=0.44) have been measured by penetration viscometry from 10~7 to 10~(13) Pa s. The temperature dependence of equilibrium viscosities in this range can be expressed approximately by a simple Arrhenius equation. Both the heat capacity change at the glass transition and the activation energy of viscous flow monotonously increase with germanium content as predicted by the Adam-Gibbs theory. Therefore, the connectivity of the germanium-sulfur network is reduced due to decreasing concentration of sulfur which causes increasing fragility of the undercooled liquid. The glass transition temperature exhibits a maximum near the GeS_2 composition where heteropolar bonds are predominantly formed.