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The effect of oxygen partial pressure, p(O2), during the post-annealing process in the fabrication of Bi-2212/Ag tapes was investigated with respect to the critical current density, Jc. high p(O2) post-annealing was performed using encapsulation techniques, autoclave furnace and an O2-hot isostatic press apparatus. The p(O2) was regulated from 1 atm up to 100 atm, and the temperature of this process was fixed at 300° C. A p(O2) of 6 atm at 300°C resulted in the highest Jc at 4.2 K. This result is consistent for the three different post-annealing techniques. A distinctive change in microstructure was not observed even though the high p(O2) post-annealing promoted oxygenation of the Bi-2212 layer. High p(O2) post-annealing improves the Jc of Bi-2212/Ag tape by decreasing electromagnetic anisotropy in the oxide layer. However, an increase in excess oxygen content produces not only a decrease in the electromagnetic anisotropy, but also a decrease in Tc of the Bi-2212 layer. The degradation of Jc by higher p(O2) post-annealing is considered to be due to the deterioration of Tc. The experimental data suggest that high p(O 2) post-annealing is one of the most effective techniques for improved Jc, and that post-annealing condition have to be optimized in order to obtain Bi-2212/Ag tape with the highest Jc. [ABSTRACT FROM AUTHOR]

• Single crystals of RuGd-1222 ((Gd,Ce) 2 Sr 2 RuCu 2 O 10−δ) were grown by the partial melting technique. • The maximum size was approximately 80 μm in length. • Superconductivity with an onset transition temperature (T c-onset) of 27 K was observed for a RuGd-1222 single-crystal lump. • The synthesis of ruthenocuprate single crystals by partial melting is anticipated to contribute to a greater understanding of this system. Growth of single crystals of RuGd-1222 ((Gd,Ce) 2 Sr 2 RuCu 2 O 10−δ) remains a major challenge, and previous studies have indicated that epitaxial thin films of these compounds exhibit deteriorated superconductivity. We have been working toward the synthesis of RuGd-1222 single crystals using the self-flux and partial melting techniques. In this paper, we report on the synthesis of RuGd-1222 single-crystal lumps by partial melting. The maximum size of a single crystal was approximately 80 μm in length, which is almost the same as that of our previous studies by self-flux method. Although these samples contained some impurity phases, the predominant phase was confirmed to be RuGd-1222. Furthermore, following optimization of the synthetic conditions, superconductivity with an onset transition temperature (T c-onset) of 27 K was observed for a RuGd-1222 single-crystal lump prepared by partial melting. Local decomposition from RuGd-1222 plate-like crystals to RuGd-1212 single crystals was observed after prolonged sintering. The synthesis of single crystals of ruthenocuprates by partial melting is expected to contribute to an improved understanding of this class of magnetosuperconductors. [ABSTRACT FROM AUTHOR]

Abstract: The FeSr2YCu2O6+δ compound with a tetragonal Ba2YCu3O6+δ -type structure exhibits superconductivity, only when it is properly annealed in N2 and subsequently in O2. N2-annealing causes the ordering of Cu and Fe, and O2-annealing supplies the carrier on the CuO2 sheets. We have synthesized a new compound FeSr2(Tb,Ce)2Cu2O8+δ with the fluorite structure instead of the Y layer between adjacent CuO2 sheets in FeSr2YCu2O6+δ . Neutron diffraction study shows that the insertion of the fluorite structure is very effective on preparing the structure with ordering of Cu and Fe without the N2-annealing. However, enough amount of carrier is not distributed on the CuO2 sheets to exhibit superconductivity, and resultingly we have observed very weak superconductivity in FeSr2(Tb,Ce)2Cu2O8+δ . [Copyright &y& Elsevier]

Abstract: Superconductivity was observed in FeSr2YCu2O6+y compounds with the reoxidization annealing and the high pressure O2 annealing. The sueprconducting transition temperature of the sample annealed in O2 of 195atm is 56K. 57Fe Mössbauer spectroscopy study revealed a suppression of Fe distribution to the Cu(2) site by the reoxidization annealing. The reoxidization annealing modifies the distribution of Fe ion and the high pressure O2 annealing introduces holes for superconductivity to the CuO2 planes. A Curie–Weiss like temperature dependence of the magnetic susceptibility was observed in the susceptibility measurement and the effective Bohr magneton is estimated to 3.3μB. A broad peak at around 20K was observed and it implies the occurrence of some magnetic ordering. [Copyright &y& Elsevier]

The spatial distributions of superconducting energy gap 2Δp have been measured at 6 K in underdoped Bi2Sr2CaCu2Ox by scanning tunneling spectroscopy. The 2Δp has been found to vary in the length scale of about 3 nm. In different regions of the cleaved surface, the average values of 2Δp are equal to each other, while the variances are different. This means that the superconducting properties in Bi2Sr2CaCu2Ox are not determined only by the carrier concentration. To characterize the superconductivity of Bi2Sr2CaCu2Ox, it is necessary to introduce a new parameter of microscopic degree of disorder, which is defined as a ratio of the variance to the average for the distribution of 2Δp. [Copyright &y& Elsevier]

An investigation was carried out into the distribution of Fe ions between Cu(1) and Cu(2) sites for FeSr 2 RECu 2 O 6 + y (RE = Eu, Er, Gd, Nd and Y), in addition to the structural, magnetic and electric properties. After a series of annealing steps to induce superconductivity, all samples exhibited a Ba 2 YCu 3 O 6 -type tetragonal crystal structure and the lattice constants increased with RE ion radius. Zero resistivity was observed for FeSr 2 YCu 2 O 6 + y , FeSr 2 ErCu 2 O 6 + y and FeSr 2 GdCu 2 O 6 + y . 57 Fe Mössbauer study revealed that for all samples except FeSr 2 NdCu 2 O 6 + y , about 10% of the Fe ions were present at Cu(2) sites. The separate three annealings are effective for FeSr 2 RECu 2 O 6 + y except FeSr 2 NdCu 2 O 6 + y for the suppression of Fe ion substitution at Cu(2) site and the carrier doping to CuO 2 plane. [ABSTRACT FROM AUTHOR]

Abstract: Li2Pd3B and Li2Pt3B show superconducting transition at the temperatures, 7.4K and 2.6K, respectively. These materials have the same cubic structure (P4332) composed of distorted octahedrons, whose corners are occupied by Pd/Pt. This structure does not have mirror or inversion symmetry along any directions. It is a very interesting feature of those materials in relation to the symmetry of superconductivity. The samples were prepared by a two-stage arc-melting method. Their superconductivity is induced by Li addition. Controlling the Li stoichiometry is a key to synthesize high quality samples in the preparation process of arc-melting because Li is volatile at high temperatures. The specific heat measurements were carried out by heat-pulse relaxation and semi-adiabatic methods. Pressure effect was measured with a SQUID magnetometer using a low temperature hydrostatic micropressure cell at pressures up to around 1GPa. The superconducting transition temperatures of both Li2Pd3B and Li2Pt3B decreased linearly with pressure. The pressure dependence, dT c/dP, were 0.091 and 0.090K/GPa, respectively. [Copyright &y& Elsevier]

A metastable superconducting phase of NbB2 with the transition temperature (Tc) around 9 K has been found in this study, although no confirmed superconductivity in the stoichiometric NbB2 has been reported since 1970s. This phase was induced by a rapid-quenching process and disappeared by annealing at 1100 °C. Since the superconducting transition was not sharp, the rapidly quenched NbB2 might contain some phases with different superconducting transition temperatures (Tcs). Niobium-deficient and -rich diborides of NbxB2 (x=0.67–1.11) were also prepared for the investigation of the compositional dependence of their Tcs. [Copyright &y& Elsevier]

Abstract: Superconductivity at 8K was reported in -FeSe with a tetragonal PbO structure but not in -FeSe with a hexagonal NiAs structure. The superconducting transition temperature was then increased up to 37K (on-set) by high pressure on polycrystalline samples. We report a study of the characterization on single crystals of FeSe superconductors. FeSe single crystals were grown using two methods, simple cooling from stoichiometric melt and flux using NaCl/KCl. While a ball-shaped aggregation composed of thick FeSe crystals was grown from the stoichiometric melt, thin hexagonal-shaped crystals with a size up to 1mm were grown using the NaCl/KCl flux. The two different crystals indicated superconductivity around at 8K in spite of their hexagonal shape, suggesting a non-superconducting compound with the NiAs-type hexagonal structure. According to the analyses using an X-ray diffractometer and a scanning electron microscope, the crystals contain microcracks that could be caused by stress. We assume that the hexagonal-shaped crystals grown at high temperature may turn partly to tetragonal -FeSe at the structure transition temperature. [ABSTRACT FROM AUTHOR]