La0.67Ca0.33MnO3: defects and conducting mechanism

Abstract We report on temperature dependence of Mn K-edge local structure studies of La 0.67 Ca 0.33 MnO 3 , its relation with the behavior at the insulator–metal oxide transition ( T IM ), and the change of conducting regime on both sides of this phase transition in samples prepared with different protocols. Our results yield strong support for the coexistence of two non-equivalent octahedra sublattices in the insulating phase, one assigned to a localized small-polaron distorted site. Below T IM we detect one average octahedron only at temperatures in which the resistivity shows its last inflection. We also find support of this picture in our small-polaron analysis of infrared optical conductivity of the same samples.