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The effects of Cu substitution for Tl in TlSr 2 Ca 2 Cu 3 O y superconductor were investigated. Nearly single-phase samples of Tl 1− x Cu x Sr 2 Ca 2 Cu 3 O y ( x =0.2−0.6) were successfully synthesized using a high pressure technique. The observed shrinkage in the lattice parameter a , concave ρ – T curve above T c and negative thermoelectric power near room temperature indicated that the Cu-substituted samples were over-doped. T c for the sample with x =0.4 increased from 73 to 94 K after annealing treatment in flowing argon gas. The Cu-substituted samples showed lower irreversibility field B irr as a function of reduced temperature than that of the pristine TlSr 2 Ca 2 Cu 3 O y [Physica C 324 (1999) 15].

The effects of the homogenizing procedure and annealing treatment on superconducting transition temperature, T c , were investigated for Zn-substituted YBa 2 Cu 3 O 7− δ . Samples of YBa 2 Cu 3− x Zn x O 7− δ ( x =0.00, 0.02, 0.05 and 0.10) were prepared under different conditions. It was found that additional pulverization and re-sintering lower T c in Zn-substituted samples. Moreover, annealing in reduced atmosphere prior to the final oxygenation further decreases T c , resulting in the lowest value ( T c =46 K for x=0.10 ) among T c ’s ever reported for Zn-substituted YBa 2 Cu 3 O 7− δ . This suggests that Zn at the Cu–O chain site moves to the CuO 2 plane by annealing samples in reduced atmosphere. Comparison of T c -suppression effects by Zn and Ni is also discussed.

We successfully prepared a single-phase sample of TlSr 2 Ca 2 Cu 3 O y by high pressure synthesis. The powder mixture with a nominal composition of TlSr 2 Ca 2 Cu 3 O 9.4 was heat-treated at 1100°C for 4 h under 6 GPa. Powder X-ray diffraction revealed that the obtained sample was single-phase of the 1223 structure with a tetragonal unit cell ( a =3.813(4) A, c =15.24(1) A). The sample exhibited Meissner signals below 86 K. The resistivity linearly decreased with decreasing temperature above 86 K and the thermoelectric power at 290 K was found to be nearly zero. These results imply that the hole concentration of the sample is nearly optimized. The sample showed an excellent dependence of the irreversibility field B irr on reduced temperature (1− T / T c ), which is comparable to that for (Cu,C)-1223.

The oxyfluoride superconductor, Sr 2 CuO 2 F 2+δ , was prepared by a sol-gel method. Two different routes were examined; one was an attempt to prepare the Sr 2 CuO 2 F 2+δ phase directly from fluorine-containing sols, and the other was the fluorination of sol-gel-derived Sr 2 CuO 3 fine powders by F 2 gas. The former route did not lead to the formation of oxyfluorides because of the precipitation of SrF 2 by the heat treatments of the gel. The latter route led to the formation of the Sr 2 CuO 2 F 2+δ phase. The amount of the Sr 2 CuO 2 F 2+δ phase and superconducting properties of the powders depended on the fluorinating condition such as F 2 gas concentration and fluorinating time. The T c values reached 45–47 K by annealing the fluorinated samples in vacuo. The magnetization hysteresis loop was measured for the first time in the oxyfluoride superconductors.

The Sr-substituted NdBa 1.5 Sr 0.5 Cu 3 O 7− δ superconductor was prepared using the sol-gel derived, highly oxidized Ba 1.5 Sr 0.5 Cu 3 O 5+ x percursor. An orthorhombic NdBa 1.5 Sr 0.5 Cu 3 O 6.9 was obtained by the reaction between Nd 2 O 3 and Ba 1.5 Sr 0.5 Cu 3 O 5.6 at 900°C under N 2 atmosphere. The superconducting transition temperatures of the sample, T c ( θ ) = 85K, T c (onset) = 90 K, and T c (end) = 84 K, were slightly higher than the reported values. The formation pass through this preparation method, the “BCO route”, and the effects of Sr substitution on the superconducting properties were discussed.

Oxyfluoride Sr 2 Cu(O,F) y thin films were prepared by a sol-gel method using Sr(O- i C 3 H 7 ) 2 and CuF 2 as starting materials and trifluoroacetic acid as an additional fluorine source. The sols were coated on SrTiO 3 (STO) or LaAlO 3 (LAO) single crystal substrates and then heated at 800°C under a condition controlled by the concentration of O 2 gas. For the films on STO, Sr 2 CuO 3 was formed first and changed to the K 2 NiF 4 -type Sr 2 Cu(O,F) y phase by post-fluorination using a methanol solution of NH 4 F. In the case of using LAO substrates, the Sr 2 Cu(O,F) y phase was directly formed by one time heating at 800°C. A direct formation of the Sr 2 Cu(O,F) y phase has never been reported before. The presence of fluorine in the films was confirmed both by chemical analysis and XPS spectroscopy. The discrepancy in the crystallization behavior of the films on STO and on LAO substrates is explained by the formation of SrF 2 impurities owing to the reaction between fluorine in the film and strontium in the STO substrate. The Sr 2 Cu(O,F) y thin films on STO exhibited the superconducting transition at 45 K in a SQUID measurement.

The preparation of the polycrystalline NdBa 2 Cu 3 O 7 − δ superconductor using Ba 2 Cu 3 O 5 + x as a precursor has been studied. Ba 2 Cu 3 O 5 + x was prepared by the sol-gel process using metal acetates as starting materials, tartaric acid as an chelating reagent and water as solvent. The gel was heated at 780°C for 60 h in O 2 to form the Ba 2 Cu 3 O 5 + x precursor. The value of x in Ba 2 Cu 3 O 5 + x was determined to be 0.5; that is, copper was in a highly oxidized state over +2. NdBa 2 Cu 3 O 7 − δ was obtained by the solid-state reaction between Nd 2 O 3 and Ba 2 Cu 3 O 5 + x heated at 900°C for 20 h in N 2 . Although the sample did not undergo post-anneal in oxygen, it showed good superconducting properties; T c of 94 K and the intragranular J c of 3.7 × 10 5 A/cm 2 under a field of 50 kOe at 20 K. The advantage of using Ba 2 Cu 3 O 5 + x is considered to be its sufficient amount of oxygen as well as prevention of the Nd 3+ /Ba 2+ substitution.

(La,Ca)(Ba,La,Ca) 2 Cu 3 O z superconducting thin films were prepared by a pulsed laser deposition method. X-ray and electron diffractions revealed that the obtained thin films had the tetragonal “123” structure. Moreover, c -axis orientation and in-plane alignment were accomplished. The films showed T c (onset)=80 K and T c (zero)=76 K in resistivity measurement. The critical current density was about 2.8×10 6 A/cm 2 at 4.2 K in zero magnetic field. The surface of the films was more stable than that of a commercial YBa 2 Cu 3 O y film in water environment.