SUPPRESSION OF SUPERCONDUCTIVITY IN R0.8PR0.2BA2CU4O8 SYSTEM

R1-xPrxBa2Cu4O8 (R=Eu, Gd, Dy, Ho, Er, Tm; x=0 and 0.2) have been inve stigated by means of X-ray diffraction and electrical-resistivity meas urements. Lattice parameters a and b increase with the increase of ion ic-radius of rare elements, and c is almost invariant. Therefore, the separation between rare-earth ions and the Cu-O2 planes will decrease with the increasing radius of the R3+ ions. in R0.8Pr0.2Ba2Cu4O8 syste m, the DELTAT(c) DELTAT(c)=T(c)(RBa2Cu4O8)-T(c)(T0.8Pr0.2Ba2Cu4O8)] we akly depends on the ionic radius of rare-earth elements, suggesting th at the hybridization between extended Pr 4f electrons and conduction b ands in the Cu-O2 planes may play weakly in R1-xPrxBa2Cu4O8. In additi on, the differences of suppression mechanisms between R1-xPrxBa2Cu4O8 and R1-xPrxBa2Cu3O7-y are discussed.