Out-of-plane transport in Bi2-xPbxSr2Co2Oy single crystals

The transport properties of Bi2−xPbxSr2Co2Oy single crystals with various Pb contents are studied. The in-plane resistivity ρab always shows metallic behavior from room temperature (290 K) to 80 K with various Pb contents, while the out-of-plane resistivity ρc shows rather complex behavior. For Pb-free samples, ρc shows semiconductive behavior in the measured temperature range. With increasing Pb content, the temperature dependence of ρc shows an evolution from semiconductive through crossover to metallic behavior. According to the formula for ρc proposed previously, the evolution of ρc behavior is fitted well. Using the small polaron theory, the complex behavior of ρc is interpreted. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)