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Superconductivity caused by oxygen reduction treatment for sintered Pr2Ba4Cu7O15–δ (Pr247) synthesized using citrate pyrolysis precursor method is examined experimentally. The sintered sample tends to be heterogeneous structure including Pr124 phase and stacking fault structure rich in CuO single chains. In this work, such a heterogeneous sample and nearly pure phase one were prepared, and the electric conductive behaviors were examined comparatively for various reduction grade sample series. In enough reduced stages, superconductivity with onset temperature 25–28 K was observed for both heterogeneous and purer samples. At transition process by the reduction, superconductivity of the heterogeneous samples can arise from lower oxygen-reduction% than purer Pr247 material. The results may possibly suggest superconductivity by CuO double chains besides Pr247 crystal in our heterogeneous ceramic system.

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.

Ceramic high- T C superconductors may be viewed as a weakly coupled random Josephson network containing the so-called π-junctions, and a chiral-glass transition is predicted to be occurred in such d-wave ceramics. In the present work, pressure dependence of the chiral-glass transition have been investigated on YBa 2 Cu 3 O 7− y and YBa 2 Cu 4 O 8 ceramics. With decreasing temperature, a superconducting order occurs at first inside each grain at T C1 and furthermore among the grains at T C2 ( T C1 ). The T C2 increases with increase of pressure, while the sharpness of the transition at T C2 does not change. In spite of differences in not only T C2 ’s but also T C1 ’s, the increasing rates of T C2 by pressure are nearly the same.

Dynamical properties of the ceramic YBa 2 Cu 3 O 7− δ have been investigated by magnetic measurements. We measured ac-susceptibilities at various frequency under zero external field and carried out dynamic scaling analysis near inter-grain transition temperature. The results exhibit scaling behavior for the critical exponents zν =8 and β =0.5. These values are fairly close to the ones for the chiral-glass estimated by Monte Carlo simulations.

Cu(2) NQR spectrum and spin-lattice relaxation rate have been measured in Y 1−x Ba 2 Cu 3 O 7 for x=0.1 and 0.2. The spectrum is different from that reported for oxygen deficient YBa 2 Cu 3 O 6+x . The relaxation rate behavior indicates that the antiferromagnetic fluctuations are suppressed because of the spin gap opening.

Successive superconductive transitions in single phase YBa 2 Cu 4 O 8 ceramics composed of homogeneous grains are examined by AC susceptibility at zero DC magnetic field. In a series of the ceramics with different sintering temperatures intrinsic critical behaviors of X ′ and X ″ are derived from the limits of X ∗ − T behavior when AC field amplitude tends to zero. Compared with the previous DC magnetization measurements, the inter-grain coupling intensity is concluded to change the location of the lower critical point but does not the essential ordering characteristic at all.

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 .

Superconducting properties are examined in Y 1−x Pr x Ba 2 Cu 4 O 8 synthesized by the citrate pyrolysis method followed by sintering in a one atm oxygen flow. Lattice constants increase linearly, while the orthorhombicity decreases linearly with increasing x. Meissner effect measurements indicate that the onset T c decrease monotonically with the Pr substitution, and disappears at x =0.75. This is caused by the change in the hole concentration with the substitution of Pr for Y.

The citrate pyrolysis method is used to investigate the synthesis process and the superconducting transitions of the YBa 2 Cu 4 O 8 (124) phase. DC susceptibility measurements show that the intrinsic Tc, both for the one bar sintering route and the 90 bar treatment, is close to 82 K. In the former case, however, the reaction temperature must not exceed 800°C, and χ ec and resistive transitions are severely degraded due to the extremely small grain size.

The annealing and quenching effects were examined on Nd 2−x Ce x CuO 4−δ after it is annealed under Ar atmosphere. The quenched samples of x=0.15 show zero resistivity at about 13K. However, zero resistance does not appear in the furnace-cooled samples. On the contrary, dc susceptibility shows that the Meissner volume fraction is nearly the same for both samples. The results indicate that superconductive connection between grains is much weaker in the furnace-cooled sample than in the quenched one.