Conductivity and dielectric relaxation in concentrated aqueous lithium chloride solutions

This paper describes a study of the recently recognized phenomenon of conductivity relaxation in liquid electrolytes as it is observed in the system LiCl+water. Advantage has been taken of the supercooling ability of 6-20m solutions in this system to reduce solution temperatures to the vicinity of -100°C and thereby to increase the relaxation time characteristic of the conductance process sufficiently to permit its study with conventional ac conductance bridges operating in the frequency range 0.2-2 000 kHz. Extensive data are presented for four solutions in the concentration range 8.3-11.9m. When the frequency-dependent conduclance and capacitance data are analyzed in the dielectric modulus notation developed by Macedo, Bose, and IJtovitz, mean relaxation times for conductance are obtained which have a non-Arrhenius temperature dependence identical to that of the dc conductivity. Earlier studies of dielectric relaxation in these solutions, carried out at room temperature and gigahertz frequencies, are re-analyzed and shown to correspond to the high-temperature extension of the same phenomenon examined at low temperatures in the present study. The characteristic migration distance associated with the conductivity relaxation time, assessed using the Nernst-Einstein equation, is of ionic dimensions. The presence of subsidiary higher-frequency relaxations is noted and their origin considered in relation to Goldstein's ubiquitous "localized motions" in glasses.