Sangoro J, Iacob C, Serghei A, Naumov S, Galvosas P, Kärger J, Wespe C, Bordusa F, Stoppa A, Hunger J, Buchner R, Kremer F
Institute of Experimental Physics I, Faculty of Physics and Geosciences, University of Leipzig, 04103, Leipzig, Germany.
J Chem Phys. 2008 Jun 7;128(21):214509. doi: 10.1063/1.2921796.
Broadband dielectric and terahertz spectroscopy (10(-2)-10(+12) Hz) are combined with pulsed field gradient nuclear magnetic resonance (PFG-NMR) to explore charge transport and translational diffusion in the 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid. The dielectric spectra are interpreted as superposition of high-frequency relaxation processes associated with dipolar librations and a conductivity contribution. The latter originates from hopping of charge carriers on a random spatially varying potential landscape and quantitatively fits the observed frequency and temperature dependence of the spectra. A further analysis delivers the hopping rate and enables one to deduce--using the Einstein-Smoluchowski equation--the translational diffusion coefficient of the charge carriers in quantitative agreement with PFG-NMR measurements. By that, the mobility is determined and separated from the charge carrier density; for the former, a Vogel-Fulcher-Tammann and for the latter, an Arrhenius temperature dependence is obtained. There is no indication of a mode arising from the reorientation of stable ion pairs.
宽带介电和太赫兹光谱（10⁻² - 10¹² Hz）与脉冲场梯度核磁共振（PFG-NMR）相结合，以探索1-丁基-3-甲基咪唑四氟硼酸盐离子液体中的电荷传输和平动扩散。介电谱被解释为与偶极摆动相关的高频弛豫过程和电导率贡献的叠加。后者源于电荷载流子在随机空间变化的势场中的跳跃，并定量拟合了观测到的谱的频率和温度依赖性。进一步的分析给出了跳跃速率，并使人们能够利用爱因斯坦-斯莫卢霍夫斯基方程推导出电荷载流子的平动扩散系数，与PFG-NMR测量结果定量一致。由此确定了迁移率并将其与电荷载流子密度分离；对于前者，得到了Vogel-Fulcher-Tammann温度依赖性，对于后者，得到了阿仑尼乌斯温度依赖性。没有迹象表明存在由稳定离子对的重新取向产生的模式。
