The conductivity of polycrystalline and monocrystalline material was measured by means of small-signal impedance spectroscopy at frequencies ranging from 5Hz to 13MHz, and temperatures of between 40 and 390C, using Cu electrodes. The single-crystal and polycrystalline samples produced well-defined single-arc spectra, as predicted for binary electrolytes in the absence of inhomogeneities, slow interfacial transfer kinetics and concentration polarization. In the case of polycrystalline samples, no evidence was found for an extra arc which was associated with slow grain-boundary transport at lower frequencies. This confirmed the general assumption that the bulk conductivity in halides was lower than, or comparable to, the conductivity along grain boundaries. The significance of earlier conductivity data which had been obtained at 1kHz, the possibility of mixed ionic and electronic conduction, and the limitations of impedance spectroscopy for the separation of ionic and electronic contributions, were considered. It was found that, when reversible electrodes of the parent metal were used, the thermodynamic state of the sample was well-defined but the electronic contribution had to be evaluated by using a complementary technique such as Hebb-Wagner polarization. A combination of the present impedance spectroscopic results with earlier polarization data indicated that ionic transport was the predominant mechanism in CuCl; at least in the temperature range which was investigated and for temperatures to which extrapolation was reasonable. The activation energies for ionic and electronic transport were compared and were found to be almost equal.

A.Brune, J.B.Wagner: Materials Research Bulletin, 1995, 30[5], 573-9