High-temperature transport properties of Ca0.98RE0.02MnO3−δ (RE=Sm, Gd, and Dy)

Abstract

We report measurements of electrical resistivity and thermopower on CaMnO3−δ and Ca0.98RE0.02MnO3−δ (RE=Sm, Gd, and Dy) prepared by solid state reaction. CaMnO3−δ exhibits nonmetal-like temperature dependence of resistivity while metal-like temperature dependence of thermopower. This inconsistency can be explained by the extrinsic carriers arising from oxygen defects using two-band model. Ca0.98RE0.02MnO3−δ exhibits metal-like temperature dependence in both resistivity and thermopower. The transition to metal-like behavior resembles the case in degenerate semiconductors and can be attributed to an impurity band formation with characteristic of hybridized Mn 3d eg and O 2p states due to electron doping via partial substitution of lanthanides for Ca2+ and oxygen defects.