Bulk and local dynamics in glass-forming liquids: A viscosity, electrical conductivity, and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi mathvariant="normal">NMR</mml:mi></mml:math>study of aluminosilicate melts

Abstract

The viscosity and electrical conductivity and the ${}^{27}\mathrm{Al}$ spin-lattice relaxation time have been measured for two calcium aluminosilicate liquids or glasses. At high temperature, the relaxation times for the three processes are the same to within experimental errors. This similarity points to a coupling between the rate of Al-O bond exchange and the structural relaxation involved in viscous flow, which also controls the motion of Ca ions that is associated with electrical conductivity. Near the glass transition, decoupling of Ca motion is indicated by the fact that the characteristic time for calcium hopping is much shorter than the structural relaxation time. For the quenched glass, the electrical conductivity is then much higher than would be predicted from extrapolation of the high-temperature equilibrium data for the melt.