[en] The recently reported superconducting YBa₂Cu₃O_y (Y123) foams are highly interesting and promising for variety of applications. In this report we present first magneto-transport measurements of the superconducting properties of these foams. The investigations reveal the superconducting properties being similar to those of bulk melt processed materials. The 123 foams reveal a T_c of 92 K and have a magnetization J_c of 40,000 A/cm² at 77 K and 0 T. The measurements of magnetic hysteresis versus field show a high anisotropy of the critical current density up to J_c^ab/J_c^c∼7

[en] The electrical performance of a hot-forming Bi:2223 compounds prepared by modifying the characteristics of the starting precursor powders and of YBa₂Cu₃O_y superconducting fabrics are investigated. The single domain Y123 fabrics are processed by an infiltration process from precursor Y₂O₃ cloths which having dimensions of thick films (∼100 μm) and posses the structure replica of precursor Y₂O₃ fabrics. Transport critical currents exceeding 2.1x10⁴ A/cm² at 77 K, 0 T and 3.9x10⁴ A/cm² at 65 K in self field are measured for Bi-2223 samples. For fabric samples, transport J_c measurements in self field showed the transition between the superconducting state and the flux-flow regime to occur at a critical current density (J_c) of 5.5x10⁴ A/cm² at 77 K. Quench tests at 77 K on the fabric samples using pulsed currents up to 5J_c with a duration of 25 ms are discussed

[en] The development of foams from a variety of substances such as polymers, glasses, metals and ceramics has led to many important applications of foam structures. A large open porosity, along with a high surface area and good mechanical properties, brings about novel properties and makes foams attractive for various applications. In addition to conventional applications such as filters, shock absorbers, heat exchangers, catalysts or lightweight constructions, porous structures are increasingly being considered for advanced functional materials, such as piezoelectrics revealing novel and improved properties. Until now, superconducting materials have not been processed in foam structures. However, a superconducting foam reveals properties which are highly interesting both for applications such as efficient heat extraction from superconducting components, e.g. in fault current limiters, and for fundamental investigations of e.g. surface pinning. We detail a manufacturing process for superconducting, pseudo-single crystalline foams of YBa₂Cu₃O_7-x (Y123) based on a combination of standard ceramic foam processing and an infiltration method. (author)

[en] We highlight recent developments in the manufacture and properties of superconducting YBa₂Cu₃O_y (Y123) fabrics prepared by an infiltration process using commercial yttria fabrics. We present the processing of single-domain Y123 fabrics in various forms such as free-standing fabrics, thick films on ceramic or metallic substrates, and in long lengths using a multi-seeding technique. In particular, controlled seeding allows for predetermined boundary junctions or single domain fabrics with controlled crystallographic orientation and tailored microstructures. Critical transport current densities (J_c) in single-domain fabrics exceed 5.5x10⁴ A cm^-2 limited by Joule heating at the contacts when passing a total dc current of 180 A at 77 K and 0 T. For multi-domain fabrics with controlled (110)/(110) grain boundaries a maximum J_c of 2.5x10⁴ A cm^-2 is observed for the best-coupled boundary junction. The room-temperature resistivity of the fabrics is about an order of magnitude lower than that of bulk monoliths. (author)

[en] By means of automated electron backscatter diffraction (EBSD) analysis, we studied the local orientations of embedded Y₂BaCuO₅ (2 1 1) particles within melt-textured YBCO samples, and also the orientations of embedded YBCO particles in directional solidified 211 samples. On both systems, we obtained high-quality Kikuchi patterns, allowing the automated mapping of the crystal orientations and a multi-phase analysis. In melt-textured YBCO with (0 0 1) orientation, we find that the embedded 211 particles do not have any preferred orientation, but the maps also reveal that at certain orientations of the 211 particles the YBCO growth is not altered. In directional solidified 211 samples, where the 211 is mainly oriented in (0 0 1) direction, the embedded YBCO particles show only some specific orientations

[en] Using the combination of standard ceramic processing and an infiltration technique, single domain superconductor foam of Y123 has been prepared. In this report we present magneto-transport measurements of these foams. The investigations reveal superconducting properties being similar to those of bulk melt processed materials. The magnetic hysteresis vs field measurements show a high anisotropy of the critical current density up to J_c^ab/J_c^c∼7, in good agreement with the observation of a strong texture as determined from neutron diffraction measurements

[en] We present the results of measurements of electrical resistivity(ρ), magnetoresistance (MR=[ρ(H)-ρ(0)]/ρ())) and DC susceptibility on polycrystalline samples of the type La_0.5Ca_0.5-xBa_xMnO₃. The substitution of larger Ba ions for Ca is seen to result in a non-monotonic variation of T_c as the system evolves from a charge-ordered insulating state for x=0.0 to a ferromagnetic metallic state for x=0.5, and this is in sharp contrast to our earlier reported results for Sr doping. The x=0.2 and 0.3 compounds show a weak increase in ρ at low temperatures (T<30K), possibly arising due to A-site ionic size mismatch between La/Ca and Ba ions. There is a significant MR for all temperatures well below T_c, but not at T_c. (author)

[en] In order to develop the superconducting wires and cables applicable at liquid nitrogen temperature in magnetic fields for next generation, we have studied basic critical current properties of newly found Re-doped Hg-based superconductors and attempted the synthesis of their grain-aligned tapes. The best tape exhibited zero resistance over 50 k Oe at 77 K, which is the record-high irreversibility field as for superconducting tapes. On the other hand, heavily Pb-doped Bi2212 superconductor was discovered to show dramatically improved critical current properties compared to the pure Bi2212. Pb-doping was found to essentially decrease the electromagnetic anisotropy resulting in a enhancement of pining strength up to high temperatures in the present system. It was suggested that the Bi(Pb) 2212 can be a promising candidate material for practical application at 40-50 K for high field generation. (author)

[en] Practical applications of high-temperature superconductors require long length and complex shapes of the textured ceramic material. The limitation of processing the REBa₂Cu₃O_y (RE-123, RE=Y, Sm, Nd, etc) superconductors in desired designs requires the development of joining techniques. In this paper we report on various attempts to join sections cut from single-domain YBa₂Cu₃O_y (Y-123) monoliths. The lower peritectic temperature rare earth Yb-123 compounds were used as solder for melt texturing at the interface for joining. The various factors influencing the formation of defect structures during the growth of the solder phase have been investigated. Transport current measurements across the joints of the samples and also of a typical configuration of a brick wall structure prepared under optimized conditions are presented. (author)

[en] We present the results of measurements of the electrical resistivity (ρ), magnetoresistance (MR) and dc and ac susceptibility (χ) of polycrystalline samples of the type La_0.5Ca_0.5-xBa_xMnO₃, synthesized under identical heat-treatment conditions. The substitution of larger Ba ions for Ca results in a non-monotonic variation of the Curie temperature (T_C) as the system evolves from a charge-ordered insulating state for x=0.0 to a ferromagnetic metallic state for x=0.5. An intermediate composition, that with x=0.1, interestingly exhibits ferromagnetic, insulating behaviour with thermal hysteresis in the ac χ at around the Curie temperature (T_C = 120 K). The x=0.2 and 0.3 compounds exhibit semiconducting-like behaviour as the temperature is lowered below 300 K, with a broad peak in ρ at around 80-100 K; these compositions exhibit a weak increase in ρ as the temperature is lowered below 30 K, indicative of electron localization effects; these compositions also undergo ferromagnetic transitions below about 200 and 235 K respectively, though these are non-hysteretic; most significantly, for these compositions, the MR is large and conveniently measurable over the entire temperature range of measurement below T_C and this experimental finding may be of interest from the applications point of view. We infer that the A-site ionic-size mismatch plays a crucial role in determining these properties. (author)