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

We report measurements of electrical resistivity and thermopower on CaMnO3-delta and Ca0.98RE0.02MnO3-delta (RE=Sm, Gd, and Dy) prepared by solid state reaction. CaMnO3-delta 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-delta 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 e(g) and O 2p states due to electron doping via partial substitution of lanthanides for Ca2+ and oxygen defects. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3593962]