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The Pr content x dependence of the superconducting transition temperature Tc is examined for various oxygen concentrations by quenching the samples of the Pr-substituted Ln1−xPrxBa2Cu3O7−y, where Ln is Y, Nd and Gd. In the case of Ln = Y, the initial rate of decrease of Tc by Pr substitution (−dTcdx) decreases with decreasing oxygen concentration for 6.6 < 7 − y < 7.0, then becomes constant for 7 − y < 6.6. In contrast, the effect of Tc-suppression by Pr in the case of Ln = Nd does not depend upon the oxygen concentration, and is much stronger than that in the case of Ln = Y. In the case of Ln = Gd, intermediate behavior between those of Y and Nd is observed, corresponding to the ionic size of Ln.

The Pr contentx dependence of the superconducting transition temperatureT c is examined for various oxygen concentrations in Ln1−x Pr x Ba2Cu3O7−y , where Ln is Nd, Gd, Ho, Y and Yb. In the case of Ln≠Nd, ionic radii of which are smaller than that of Pr, the initial rate of decrease ofT c by Pr substitution (-dT c /dx) decreases with decreasing oxygen concentration for 6.6

The oxygen concentration dependence of T c is examined in Y 1−x Pr x Ba 2 Cu 3 O 7− y . The T c decreases with decreasing the oxygen concentration 7− y in not only Ortho I (6.75≦7− y ≦7.0) but also the region between Ortho II and Tetra (7− y ≦6.6) for the Pr contents of 0≦ x T c increases conversely with decrease of 7− y for 0.3≦ x y ≦6.75). The Pr content dependence of T c for Ortho II is quite different from that for Ortho I, and is preferably similar to that in the stoichiometric oxide superconductor Y 1−x Pr x Ba 2 Cu 4 O 8 .