Contributions of CuO planes and CuO chains on the transport

We have investigated the contributions of CuO planes and CuO chains on the transport properties of YBa Cu O by 2 2 4 8 Ž . Ž . measuring the electrical resistivity and thermoelectric power S of Y Pr Ba Cu Zn O , Y Ca Ba Cu O and 1yx x 2 1yy y 4 8 1yx x 2 4 8 Ž . YBa Cu Ga O . Pr reduces the mobile carrier concentration in the CuO planes in YBa Cu O , as a consequence, the 2 1yx x 4 8 2 2 4 8 Ž . 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 Ž . 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 Ž . introduces holes in the CuO planes. However, the substitution of Ga in Cu 1 -site suppresses the carrier concentration in 2 CuO chains and increases the normal-state resistivity revealing the important contribution from CuO chains on the metallic behavior of YBa Cu O and PrBa Cu O . q 1999 Published by Elsevier Science B.V. All rights reserved. 2 4 8 2 4 8 Ž .