Correlation between electrical conductivity, viscosity, and structure in borosilicate glass-forming melts

The electrical conductivity and viscosity of borosilicate glass-forming melts were studied over a wide composition and temperature range above the transition temperature Tg. High-temperature Raman spectroscopy was used to characterize the structure of both molten and glassy states of the system. The temperature dependence of both electrical conductivity and viscosity are well described by a Vogel-Tammann-Fulcher (VTF) law. Contrary to the solid state, it appears that in the molten state the boron coordination number is no longer the relevant parameter to account for the compositional dependence of both the electrical conductivity and the viscosity. Our results reveal an interdependence of the electrical conductivity and viscosity with a nonlinear character of the Stokes-Einstein law. This could be explained by a difference in the elementary mechanism of transport between these two properties.