ANISOTROPIC ELECTRICAL-RESISTIVITY AND OXYGEN ANNEALING EFFECT ON IT IN LA2-XCAXCUO4 SINGLE-CRYSTALS

The oxygen annealing effect on the temperature-dependent electrical resistivity has been studied in La1.91Ca0.09CuO4-y single crystals grown by the TSFZ method. In as-grown crystals, semiconducting-like electrical conduction has been observed, both in the ab-plane and the c-axis at the non-superconducting state. The onset transition temperature T-c-onset was about 17.5 K. After annealing in oxygen, rho(ab)(T) becomes metallic and shows a resistivity minimum at a certain temperature T-min that separates regions of metallic behavior at T>T-min from semiconducting behavior at T<T-min, while rho(c)(T) remains semiconducting. In the low-temperature region, an upward curvature of the resistivity (rho(ab)(T)) has been observed with decreasing temperature below T-min. This is an indication of the occurrence of weak electron localization due to the randomness of the oxygen distribution in the crystal lattice caused by oxygen deficiency that might still be present in the annealed samples. The Anderson-Zou fit to the data works well in metallic samples and the variable range hopping law (VRH) in non-metallic samples.