Electrical conduction through bond percolation in Nd0.67Sr0.33MnO3

We report our analysis of resistivity data on Nd0.67Sr0.33MnO3 polycrystalline samples as a function of preparative conditions using a bond percolation model for a random mixture of metallic and insulating regions, assuming polaronic transport above and below the metal–insulator (M–I) transition temperature. Our analysis suggests that for oxygen deficient compounds the M–I transition that occurs at a lower temperature than the ferromagnetic transition arises from a percolation of the metallic regions. The temperature dependence of resistivity and thermopower suggests the existence of a bimodal distribution of conductivities.