.Physica C 312 1999 55–60 Contributions of CuO planes and CuO chains on the transport2

We have investigated the contributions of CuO planes and CuO chains on the transport properties of YBa Cu O by2 2 4 8 . .measuring the electrical resistivity and thermoelectric power S of Y Pr Ba Cu Zn O, Y Ca Ba Cu O and1yx x 2 1yy y 4 8 1yx x 2 4 8 .YBa Cu Ga O. Pr reduces the mobile carrier concentration in the CuO planes in YBa Cu O, as a consequence, the2 1yx x 4 8 2 2 4 8 .superconducting transition temperature is progressively decreased with increasing Pr. The S T data suggest that the metallic behavior at lower temperature of the Pr and Zn doped compounds is contributed by the double CuO chains. On the other .hand, the S T behavior of Ca doped samples is opposite to that of the Pr doped samples because the doping of Ca in Y-site .introduces holes in the CuO planes. However, the substitution of Ga in Cu 1-site suppresses the carrier concentration in2 CuO chains and increases the normal-state resistivity revealing the important contribution from CuO chains on the metalli