Magnetoresistance of polycrystalline Ba2YCu3O7 and Ba2Y1-xLnxCu3O7 (Ln=Pr,Ho,Gd, or Eu) are measured from Tc to 230 K. All the samples show large positive magnetoresistance arising from superconducting fluctuation. The temperature dependence is well-described by the recently developed theory which includes the Zeeman contribution of the Maki-Thompson-term. in pure samples, the coherence lengths along the ab axis and c axis are 12 Å and 2 Å, respectively. The phase relaxation time is estimated to be 2×10-13 sec at 100 K. Only Pr substitution shortens the phase relaxation time, indicating the pair breaking nature of the Pr ion.
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