Electrical conductivity and translational diffusion in the 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid

Abstract

Broadband dielec. and terahertz spectroscopy (10-2-10+12 Hz) are combined with pulsed field gradient NMR (PFG-NMR) to explore charge transport and translational diffusion in the 1-butyl-3-methylimidazolium tetrafluoroborate ionic liq. The dielec. spectra are interpreted as superposition of high-frequency relaxation processes assocd. with dipolar librations and a cond. contribution. The latter originates from hopping of charge carriers on a random spatially varying potential landscape and quant. fits the obsd. frequency and temp. dependence of the spectra. A further anal. delivers the hopping rate and enables one to deduce-using the Einstein-Smoluchowski equation-the translational diffusion coeff. of the charge carriers in quant. agreement with PFG-NMR measurements. By that, the mobility is detd. and sepd. from the charge carrier d.; for the former, a Vogel-Fulcher-Tammann and for the latter, an Arrhenius temp. dependence is obtained. There is no indication of a mode arising from the reorientation of stable ion pairs. (c) 2008 American Institute of Physics