The transport properties of Bi 2-x Pb x Sr 2 Co 2 O y single crystals with various Pb contents are studied. The inplane resistivity ρ ab always shows metallic behavior from room temperature (290 K) to 80 K with various Pb contents, while the out-of-plane resistivity ρ c shows rather complex behavior. For Pb-free samples, ρ c shows semiconductive behavior in the measured temperature range. With increasing Pb content, the temperature dependence of ρ c shows an evolution from semiconductive through crossover to metallic behavior. According to the formula for ρ c proposed previously, the evolution of ρ c behavior is fitted well. Using the small polaron theory, the complex behavior of ρ c is interpreted.

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