Suppression of superconductivity in R0.8Pr0.2Ba2Cu4O8 system

R1-xPrxBa2Cu4O8 (R=Eu, Gd, Dy, Ho, Er, Tm; x=0 and 0.2) have been investigated by means of X-ray diffraction and electrical-resistivity measurements. Lattice parameters a and b increase with the increase of ionic-radius of rare-earth 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 system, the ΔTc [ΔTc=Tc(RBa2Cu4O8)-Tc(R0.8Pr0.2Ba2Cu4O8)] weakly depends on the ionic radius of rare-earth elements, suggesting that the hybridization between extended Pr 4f electrons and conduction bands in the Cu-O2 planes may play weakly in R1-xPrxBa2Cu4O8. In addition, the differences of suppression mechanisms between R1-xPrxBa2Cu4O8 and R1-xPrxBa2Cu3O7-y are discussed. (orig.)