TRANSPORT AND MAGNETIC-PROPERTIES OF THE (EU,CE)2(BA,EU)2CU3O9-DELTA-TYPE AND TSTAR-TYPE SUPERCONDUCTORS - DEPENDENCE OF TC ON THE SIZE OF THE RARE-EARTH ION

The electrical transport properties and magnetic susceptibility of (L2/3Ce1/3)2(La1/3Ba1/3Sr1/3)2Cu3O9-delta (2:2:3 phase) where L is a rare-earth element are measured and compared with those of the T* phase (Nd1.4Ce0.2Sr0.4Cu1-xZnxO4-delta and La1.8-xLxSr0.2CuO4-delta) in order to investigate why the superconducting transition temperature (T(c)) depends on the ionic radius of the atom L. For 2:2:3 samples with L = Eu, Dy, Y, or Ho, the smaller the size of the L3+ ion, the lower is the value of T(c), while the Hall coefficient (R(H)) remains at the same level at temperatures above 130 K. This is in contrast to the case of La1.8-xLxSr0.2CuO4-delta with L = Sm, Eu, or Gd, in which the decrease in T(c) with decreasing ionic radius of the L atom may be attributed to the reduction in the carrier concentration. The resistivity, R(H), and Seebeck coefficient for a nonsuperconducting 2:2:3 sample containing small L3+ ions are all parallel to those of a nonsuperconducting T*-phase sample with Zn doping. Judging from these experimental results, we suggest that a "disordered potential" similar to the case of the Zn-doped T*-phase compound exists in the nonsuperconducting 2:2:3 compound.