Non-Arrhenius viscosity related to short-time ion dynamics in a fragile molten salt

Abstract

The equation T·σ_DC(T) = α·exp[−(E*/k_BT) − γ·exp(E*/k_BT)] has been used to understand the non-Arrhenius behaviour of the DC conductivity in supercooled glass-forming melts. Here, α, γ and E* are parameters, E* denoting the activation energy for an elementary displacive step. Unlike the empirical VTF relation, our equation provides a link between the long-time and the short-time ion dynamics as observed in broad-band conductivity spectra. Surprisingly, the same equation with the same value of E* but different γ successfully describes the fluidity (inverse viscosity) of a fragile glass-forming melt. This opens up the possibility of relating non-Arrhenius viscosities to short-time properties, which is in agreement with recent experimental and computer-simulation results.