Microcontact impedance measurements of individual highly conductive grain boundaries: General aspects and application to AgCl

An impedance technique is presented using microelectrodes to quantitatively investigate bulk and grain boundary properties of polycrystals with highly conductive grain boundaries. The connections between the experimentally available resistance data and the local grain boundary properties are achieved by finite element simulations. Experiments on polycrystalline AgCl are presented which demonstrate the applicability of the method and permit the determination of the ionic conductivity enhancement at the grain boundaries. Under the assumption that an enhanced Ag vacancy concentration in the space charge layer is the origin of the increased conductivity, the space charge potential is determined to be 300 mV.