Ionic conductivity and microwave dielectric relaxation of lithium hexafluoroarsenate (LiAsF6) and lithium perchlorate (LiClO4) in dimethyl carbonate

Abstract : Audiofrequency electrical conductivity data are reported in the solvent dimethylcarbonate (DMC) at 25 deg C in the concentration range 0.0001 to 1M for LiAsF6 and 0.0001 to 0.3M for LiClO4. From 0.0001 to approx. = 0.01M the data are interpreted by the Fuoss-Kraus triple-ions theory leading to the values of the ion pair formation constant Kp and triple ion formation constant KT. For the data at higher concentration, it is shown that the change of static permittivity of the solution (due to the presence of solute ion-pairs and other polar species, which increase the polarization of the solution) can account qualitatively for the behavior of the conductance data and their deviation from the Fuoss-Kraus theory. These deviations are mostly due to changes in permittivity, not accounted for in the conventional treatment of the data, rather than by the failure of the theory. Introduction of the quadrupole formation constant is necessary, however, for LiAsF6 for a more quantiative treatment of the conductance data. Microwave complex permitivities in the concentration range 0.05M to 0.3M, frequency range approx. = 1 to 90- GHz are intepreted by two Debye relaxation processes, one due to the solute and one to the solvent. For LiAsF6 the Boettcher plot, (expressing a quantity related to the change of the relaxation strength with the concentration of electrolyte), is nonlinear with the concentration. Keywords include: Electrical conductance, and Microwave dielectric relaxation.