Temperature dependence of electrical resistivity for Ca-doped perovskite-type Y1−xCaxCoO3 prepared by sol–gel process

The temperature dependences of DC electrical resistivity for perovskite-type oxides Y1−xCaxCoO3 (0⩽x⩽0.1), prepared by sol–gel process, were investigated in the temperature range from 20 K up to 305 K. The results indicated that with increase of doping content of Ca the resistivity of Y1−xCaxCoO3 decreased remarkably, which was found to be caused mainly by increase of carrier (hole) concentration. In the whole temperature range investigated the temperature dependence of resistivity ρ(T  ) for the un-doped (x=0x=0) sample decreased exponentially with decreasing temperature (i.e. ln ρ∝1/T  ), with a conduction activation energy Ea=0.308eV; the resisitivity of lightly doped oxide (x=0.01x=0.01) possessed a similar temperature behavior but has a reduced Ea (0.155 eV). Moreover, experiments showed that the relationship ln ρ∝1/T existed only in high-temperature regime for the heavily doped samples (T≳82 and ∼89 K for x=0.05x=0.05 and 0.1, respectively); at low temperatures Mott's ln ρ∝T−1/4 law was observed, indicating that heavy doping produced strong random potential, which led to formation of considerable localized states. By fitting of the experimental data to Mott's T−1/4 law, we estimated the density of localized states N(EF) at the Fermi level, which was found to increase with increasing doping content.