The electrical conductivity of single and polycrystalline copper(I) chloride

Abstract

The electrical conductivity of polycrystalline and single crystal CuCl has been measured by small-signal impedance spectroscopy in the frequency range from 5Hz to 13 MHz, at temperatures between 40 °C and 390 °C, with copper electrodes. Single-crystal and polycrystalline samples rendered well-defined single arc spectra, as predicted by J.R. Macdonald for binary electrolytes in the absence of inhomogeneities, slow interfacial transfer kinetics and concentration polarization. In polycrystalline samples no evidence of an extra arc associated with slow grain-boundary transport was found at lower frequencies, which confirms the general assumption that the bulk conductivity in halides is lower than or comparable to the conductivity along the grain boundaries. The significance of earlier conductivity data on CuCl obtained at 1 KHz is assessed. The possibility of mixed ionic and electronic conduction in CuCl is considered, and the limitations of impedance spectroscopy to separate ionic and electronic contributions are discussed. When reversible electrodes of the parent metal are used, as in the present case, the thermodynamic state of the sample is well-defined, but electronic contributions need to be evaluated with a complementary technique, e.g. the Hebb-Wagner polarization technique. The combination of the results here obtained by impedance spectroscopy with earlier polarization data indicate that ionic transport is the dominant mechanism in CuCl, at least in the temperature range investigated and also for temperatures at which an extrapolation is reasonable. Activation energies for ionic and electronic transport are compared and found nearly equal.