Contributions of CuO2 planes and CuO chains on the transport properties of YBa2Cu4O8

We have investigated the contributions of CuO2 planes and CuO chains on the transport properties of YBa2Cu4O8 by measuring the electrical resistivity and thermoelectric power (S) of Y1-xPrxBa2(Cu1-yZny)(4)O-8, Y1-xCaxBa2Cu4O8 and YBa2(Cu1-xGax)(4)O-8. Pr reduces the mobile carrier concentration in the CuO2 planes in YBa2Cu4O8, as a consequence, the 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 CuO2 planes. However, the substitution of Ga in Cu(1)-site suppresses the carrier concentration in CuO chains and increases the normal-state resistivity revealing the important contribution from CuO chains on the metallic behavior of YBa2Cu4O8 and PrBa2Cu4O8. (C) 1999 Published by Elsevier Science B.V. All rights reserved.