[en] MgO particles were introduced into (Bi,Pb)₂Sr₂Ca₂Cu₃O_10+δ powder in various weight fractions. Bulk samples were made from the Bi2223/MgO powder and heat-treated at various temperatures. The phase formation and the microstructure were studied for different amounts of MgO and for different sintering conditions. It was found that, below 845 deg. C, the ratio of Bi2223 phase decreased when the amount of MgO increased. The addition of MgO caused the Bi2201 phase content to decrease via an increase of the liquid viscosity. The presence of MgO influenced the microstructure of the samples and decreased the mean size of Bi2223 grains. The effects of the MgO addition on the intergranular critical current density, J_c as a function of magnetic field was investigated by magnetisation hysteresis measurements. MgO presence significantly expands the magnetisation hysteresis loop and thus increases J_c for amount of MgO, which does not exceed 15 wt.%

[en] Bulk-textured Bi2223 superconductors with high density have been successfully formed by the hot stacking-forging process. The grain orientation was verified by textural analysis, scanning electron microscopy observation and the critical field deduced from magneto-resistivity measurements. Transport critical current data of the textured superconductor samples were obtained using DC-measurements. According to current-voltage curves, the transition between the superconducting state and the flux-flow regime corresponds to a high transport critical current density (J_c) up to 2 x 10⁴ A/cm² at 77 K in a self-field. In addition, J_c, values were measured at various temperatures and different applied magnetic fields. Several textured pieces were hot-stacked under various applied stresses. This procedure leads to an increase of the sample thickness and the nominal engineering critical current (I_c) in order to use textured-Bi2223 for practical power generation

[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] Dense Bi2223 superconductors have been successfully formed by hot stacking-forging process (HSF). Neutron diffraction measurements were used to investigate the bulk textures of HSF-Bi2223 samples. Angular dependence of transport critical current density, J_c values were measured at various temperatures and different applied magnetic fields. Several textured pieces were hot-stacked. This procedure leads to an increase of both the sample thickness and the nominal engineering critical current (I_c), favourable hints for use of textured-Bi2223 in power generation supplies

[en] This paper deals about the texture analysis of sinter-forging (Bi, Pb)₂Sr₂Ca₂Cu₃O_10+δ (Bi2223) discs and YBa₂Cu₃O_7-x (Y123) foams. Orientation distributions were measured by X-ray and neutron diffraction respectively. In the case of Bi2223 samples, an overview of our results is presented. It reflects clearly the importance to combine physical measurements and texture analysis. Several factors as the size of the precursor powder and the process parameters influence significantly the crystallite orientation and consequently the final properties of the textured discs. In the case of Y123 foams, the only usable non destructive diffraction characterisation is the combined approach, and we show what it can bring on one example

[en] Thermoelectric performances on cobaltite ceramics can be changed by grain orientation. This can be performed by directional solidification on samples prepared from different synthetic methods. Three synthetic methods, conventional solid state reaction, sol-gel and polymer solution were used for preparation of Bi₂Ca₂Co₁.7O_x powders. The powders have been directionally grown, at a rate of 30 mm/h, by the laser floating zone method. In all the cases, the microstructure shows alternated layers, of Bi₂Ca₂Co₂O_x and a Bi-Ca-O solid solution, with small CoO inclusions. It has been found an improvement on the power factor at 50 degree centigrade for the solution methods with respect to the conventional solid sate sintered samples. (Author)

[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 effect of precursor powder assemblage on the phase formation, crystallite orientation and transport critical current density of Bi2223 textured discs has been studied. We observe that starting powder composed of Bi2212 and secondary phases results in a stronger grain alignment than if composed of nearly pure Bi2223. SEM observations and XRD analyses show that the liquid phase produced during the sinter-forging step is essential to achieve sharp orientation distributions and high critical current densities

[en] Thermo electrical properties of cobaltate ceramics can be tuned up by choosing the adequate synthetic method, cation substitution and subsequent grain orientation. This can be performed preparing the ceramics by a polymer solution method, using Pb partially substituting Bi, and texturing by directionally growing from the melt. In this work, Bi₂-xPb_xCa₂Co₁.7O_y (x 0.0, 0.2, 0.4 and 0.6) ceramics, prepared by a polymer solution method, have been directionally grown, with the Laser Floating Zone (LFZ) technique, at 30 mm/h. In all the cases, the microstructure shows alternated layers with small CoO inclusions. It has been found a very important decrease on the resistivity and, at the same time, on the thermopower. However, the power factor values are improved with Pb addition, reaching power factor values, for samples with 0.4 Pb substitution, as high as two times the values obtained for undoped ones. (Author) 30 refs.

[en] Most of NdBaCuO synthesis were realized under oxygen controlled melt growth (OCMG) which allows to avoid the solid solution formation. However, for industrial applications air synthesis is preferable due to its simplicity and its cost. In this work, different seeds and thermal cycles have been investigated in order to optimize the nucleation conditions for the obtention of a single domain. Several criteria have been defined for the choice of the seed. The solid solution Nd_1+xBa_2-xCu₃O_y formed in these air synthesised samples appears in the range of x = 0.10 to 0.15, corresponding to T_conset between 60 K and 80 K. The nominal composition and the synthesis conditions (substrate, thermal treatments.) have to be accurately defined in order to avoid neodymium-rich solid solution formation. (orig.)