On the localized impedance spectroscopic characterization of grain boundaries: General aspects and experiments on undoped SrTiO3

Impedance measurements using microelectrodes on adjacent grains of polycrystals are a valuable tool for a detailed analysis of grain boundary properties of ceramic materials. In order to support proper interpretation of such experiments two fundamental aspects are discussed in the theoretical part of this paper: first, it is shown that “localized” experiments using contact pads are often not reasonable and can lead to severe misinterpretation. Second, results from finite element calculations illustrate as to how far conclusions on the grain boundary resistivity distribution can be drawn from a measured grain boundary resistance statistics. In the experimental part, microelectrode impedance measurements and orientation imaging data on undoped polycrystalline SrTiO3 are presented and interpreted in terms of the homogeneity of the space charge potentials at grain boundaries.