Grain boundary conductance in AgCl gained by micro-contact impedance spectroscopy

Local conductivity of sintered AgCl polycrystals was studied using micro-contact impedance spectroscopy. The technique is based on the flux constriction effect, which involves probing of the sample solely in the vicinity of the microelectrode. By contacting the polycrystal surface at different points, we could distinguish between the grains and the highly conductive grain boundaries. Temperature-dependent measurements revealed that the grain conductivity resembles that of single crystals, showing clearly the extrinsic and intrinsic behaviour. On the contrary, the grain boundary conductance exhibits the same activation energy over the whole temperature range studied. These results go along with the ionic space charge model. Conductivity data obtained from micro-contact and conventional impedance spectroscopy allow a quantitative verification of the brick layer model.