On the Conductivity of Polycrystalline Materials

Expressions for the conductivity and impedance of polycrystalline materials are given for a greatly simplified grain distribution topology. We include not only contributions from the bulk and the proper grain boundary, but also series and parallel contributions from the space charge regions surrounding the grain boundaries. The relations obtained are applied to conductance measurements of bicrystalline and of ceramic ionic conductors (silver halides). ‐ It is shown that the space‐dependent grain boundary conductivity can be taken account of to a first approximation by introducing effective charge carrier concentrations and an effective width, and thus normal resistor‐elements. The experiments give evidence for both the presence of highly conductive space charge layers adjacent to the grain boundaries (manifesting in the high frequency impedance semi‐circle) and the presence of less conductive core regions (manifesting in the low frequency circle) in the silver halides.