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 p(T) for the un-doped (x = 0) sample decreased exponentially with decreasing temperature (i.e. ln p proportional to 1/T), with a conduction activation energy E-a = 0.308 eV; the resisitivity of lightly doped oxide (x = 0.01) possessed a similar temperature behavior but has a reduced E-a (0.155 eV). Moreover, experiments showed that the relationship ln rho proportional to 1/T existed only in high-temperature regime for the heavily doped samples (T greater than or similar to 82 and similar to 89 K for x = 0.05 and 0.1, respectively); at low temperatures Mott's ln rho proportional to 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(E-F) at the Fermi level, which was found to increase with increasing doping content. (c) 2006 Elsevier Ltd. All rights reserved.