Breakdown of the fractional Stokes-Einstein relation in silicate liquids

The fractional Stokes-Einstein relation postulates a direct relationship between conductivity and shear flow. Like viscosity, the electrical resistivity of a glass-forming liquid exhibits a non-Arrhenius scaling with temperature. However, while both viscosity and resistivity are non-Arrhenius, here we show that these two properties follow distinct functional forms. Through analysis of 821 unique silicate liquids, we show that viscosity is best represented using the Mauro-Yue-Ellison-Gupta-Allan (MYEGA) model, whereas the resistivity of the same compositions more closely follows the Avramov-Milchev (AM) equation. Our results point to two fundamentally different mechanisms governing viscous flow and conductivity and therefore cast doubt on the general validity of the fractional Stokes-Einstein relation. (C) 2011 Elsevier B.V. All rights reserved.