Universal charge transport of the Mn oxides in the high temperature limit

We have found that various Mn oxides have the universal resistivity and thermopower in the high temperature limit. The resistivities and thermopowers of all the samples go toward constant values of 7+/-1 mOmega cm and -79+/-3 muV/K, which are independent of carrier density and crystal structures. We propose that the electric conduction occurs in a highly localized way in the high temperature limit, where the exchange of entropy and charge occurs in the neighboring Mn3+ and Mn4+ ions. (C) 2004 American Institute of Physics.