SUPERCONDUCTING PROPERTIES OF (Y1-XPRX)BA2CU4O8 COMPOUNDS

(Y1-xPTx)Ba2Cu4O8 compounds with x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, and 0.7 were synthesized using a high-pressure oxygen technique. The s olubility limit x(s) in this compound system was found to be 0.7. In t his composition range, (Y1-xPrx)Ba2Cu4O8 compounds have the YBa2Cu4O8( 124) structure and the lattice parameters a, b and c increase with inc reasing Pr content x. The superconducting transition temperature T-c d ecreases monotonically with increasing x, and the critical content x(c ), where superconductivity disappears, has been estimated to be 0.8. T here is an obvious effect of Pr substitution on superconductivity, alt hough the effect is smaller in the 124 system than that in the 123 sys tem. X-ray diffraction results suggest that Pr is almost 3+ in this sy stem. A model for the Pr substitution is suggested to make holes immob ile to suppress superconductivity as the result of the hybridization o f O 2p(x) with Pr 4f orbitals.