Nonlinear ion transport at high electric field strengths in the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide

Impedance spectroscopy at high electric field strengths ranging from 73 kV/cm to 146 kV/cm was used to measure the low-field conductivity and third-order nonlinear conductivity of the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C6mim] [NTf2]. The measurements were carried out at three different temperatures close to the glass-transition temperature Tg = 189 K. The third-order conductivity coefficient σ3′ was determined from higher-order harmonic contributions to the measured ionic currents. Apparent jump distances aapp derived from the low-field and the third-order dc conductivity were found to be similar to those derived for solid electrolytes. However, in contrast to various solid electrolytes, the frequency-dependent third-order conductivity σ3′ shows no change in sign in the crossover regime to dc to dispersive conductivity.