The electronic conductivity of lead fluoride and the D.C. Polarization theory

The electronic conduction characteristics of solid lead fluoride were investigated using the Wagner d.c. polarization technique. It was found that when the (?) Pb/PhF₂/graphite ( + ) cell was polarized at potentials much below a critical value, E_c, the steady state current, I, as a function of the polarization potential, E, behaves in accordance with the Wagner equation. The log I vs E plots gave straight lines with slopes having the theoretical value of F/2.303 RT. On the other hand, when the polarization potential was equal or higher than E_c, an anomalous behavior was observed. Slopes with values less than the theoretical were obtained from the log I vs E plots. This anomalous behavior was attributed to the high concentration of electron holes at the PbF₂/graphite interface resulting from the high polarization potential. The critical potential was defined as the applied potential where the electron hole concentration at the PbF₂/graphite interface becomes so high that the electronic conductivity is equal to the ionic conductivity which contradicts the assumptions for the Wagner equation. Consequently, the Wagner equation is not applicable under these conditions.