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We synthesized the samples $Ba_{1-x}M_xFe_2As_2$ (M=La and K) with$ThCr_2Si_2$-type structure. These samples were systematically characterized byresistivity, thermoelectic power (TEP) and Hall coefficient ($R_H$).$BaFe_2As_2$ shows an anomaly in resistivity at about 140 K. Substitution of Lafor Ba leads to a shift of the anomaly to low temperature, but nosuperconducting transition is observed. Potassium doping leads to suppressionof the anomaly in resistivity and induces superconductivity at 38 K as reportedby Rotter et al.\cite{rotter}. The Hall coefficient and TEP measurementsindicate that the TEP is negative for $BaFe_2As_2$ and La-doped $BaFe_2As_2$,indicating n-type carrier; while potassium doping leads to change of the signin $R_H$ and TEP. It definitely indicates p-type carrier in superconducting$Ba_{1-x}K_xFe_2As_2$ with double FeAs layers, being in contrast to the case of$LnO_{1-x}F_xFeAs$ with single FeAs layer. A similar superconductivity is alsoobserved in the sample with nominal composition $Ba_{1-x}K_xOFe_2As_2$.

Transport properties and superconductivity in $Ba_{1-x}M_xFe_2As_2$ (M=La and K) with double FeAs layers