Origin of electrically heterogeneous microstructure in CuO from scanning tunneling spectroscopy study

We report electronic structure of the grains and grain boundaries (GBs) of the high permittivity (kappa similar to 10(4)) ceramic CuO from scanning tunneling spectroscopy (STS) studies. The p-type semiconducting character of the CuO grains and insulating behavior of the corresponding GBs, observed from STS studies, have been explained. This type of electrically inhomogeneous microstructure leads to the formation of barrier layer capacitance elements in CuO and, hence, provides an explanation of the colossal-kappa response exhibited by CuO. (c) 2008 American Institute of Physics.