Inter- and intragrain currents in bulk melt-grown YBaCuO rings

A simple contactless method suitable to discern between the intergrain (circular) current, which flows in the thin superconducting ring, and the intragrain current, which does not cross the weakest link, has been proposed. At first, we show that the intergrain current may directly be estimated from the magnetic flux density $B(\pm z_0)$ measured by the Hall sensor positioned in the special points $\pm z_0$ above/below the ring center. The experimental and the numerical techniques to determine the value $z_0$ are discussed. Being very promising for characterization of a current flowing across the joints in welded YBaCuO rings (its dependencies on the temperature and the external magnetic field as well as the time dissipation), the approach has been applied to study corresponding properties of the intra- and intergrain currents flowing across the $a$-twisted grain boundaries which are frequent in bulk melt-textured YBaCuO samples. We present experimental data related to the flux penetration inside a bore of MT YBaCuO rings both in the non-magnetized, virgin state and during the field reversal. The shielding properties and their dependence on external magnetic fields are also studied. Besides, we consider the flux creep effects and their influence on the current re-distribution during a dwell.Comment: 13 pages, 16 figures (EPS), RevTeX4. In the revised version, corrections to perturbing effects near the weak links are introduced, one more figure is added. lin

Li and Ce doping of melt-textured YBCO: Improved jc at medium fields

International audienceThe top seeded melt textured growth method was applied to a Ce doped YBCO material with a partial substitution of Cu with Li. The amount of Li in the samples varied from 0.25 to 0.05 at% relative to the copper atoms. The change of Tc and jc compared to a reference sample was measured using SQUID magnetometer. Field induced pinning was indicated by elevated jc in the jc(B) curve. The peak effect at 77 K appeared in the moderate field region around 0.5 T. Optimal lithium content was determined to be at 0.05 at%. Final Li content in textured bulk material was verified with atomic absorption

Li and Ce doping of melt-textured YBCO: Improved jc at medium fields

International audienceThe top seeded melt textured growth method was applied to a Ce doped YBCO material with a partial substitution of Cu with Li. The amount of Li in the samples varied from 0.25 to 0.05 at% relative to the copper atoms. The change of Tc and jc compared to a reference sample was measured using SQUID magnetometer. Field induced pinning was indicated by elevated jc in the jc(B) curve. The peak effect at 77 K appeared in the moderate field region around 0.5 T. Optimal lithium content was determined to be at 0.05 at%. Final Li content in textured bulk material was verified with atomic absorption

Spark plasma texturing (SPT) of p-type [Ca2CoO3]0.62[CoO2] thermoelectric oxide

Hole-doped [Ca2CoO3]0.62[CoO2] (Co349) thermoelectric materials were densified and textured by spark plasma sintering (SPS) process. Thin pre-sintered Co349 lamellar samples were used to process textured monoliths. The textured thin monoliths were further used in obtaining samples with increased thickness for anisotropic property studies by hot-stacking as multiple layers. Infrared measurements were used to investigate the presence of carbon diffused from the SPS tool into the bulk of the sample. The phase compositions, grain texture, as well as microstructure of the samples were analyzed by X-ray diffraction and SEM studies. The high temperature thermoelectric transport properties of the bulk samples and the correlation between the grain orientations, structural and anisotropy of thermoelectric properties were discussed in detail. The textured sample processed by SPT shows the power factor value of 450 μW m-1 K-2 at 600 °C which is 30% higher than the corresponding value for SPS one and eight times larger than samples conventionally sintered. © 2016 Elsevier B.V. All rights reserved

Spark plasma texturing (SPT) of p-type [Ca2CoO3]0.62[CoO2] thermoelectric oxide

International audienceHole-doped [Ca2CoO3]0.62[CoO2] (Co349) thermoelectric materials were densified and textured by spark plasma sintering (SPS) process. Thin pre-sintered Co349 lamellar samples were used to process textured monoliths. The textured thin monoliths were further used in obtaining samples with increased thickness for anisotropic property studies by hot-stacking as multiple layers. Infrared measurements were used to investigate the presence of carbon diffused from the SPS tool into the bulk of the sample. The phase compositions, grain texture, as well as microstructure of the samples were analyzed by X-ray diffraction and SEM studies. The high temperature thermoelectric transport properties of the bulk samples and the correlation between the grain orientations, structural and anisotropy of thermoelectric properties were discussed in detail. The textured sample processed by SPT shows the power factor value of 450 μW m-1 K-2 at 600 °C which is 30% higher than the corresponding value for SPS one and eight times larger than samples conventionally sintered. © 2016 Elsevier B.V. All rights reserved

Extruded YBCO HTS Single Domain Bulk Materials for Permanent Magnets

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Superconducting Properties of MgB2 Bulk Shaped by Spark Plasma Sintering

International audienceMgB2 bulk superconductors were shaped by Spark Plasma Sintering (SPS) process and the superconducting properties were measured. The obtained materials were 98% dense. Trapped field higher than 1.4 T was measured at 20 K. Otherwise, the possibility to use MgB2 for magnetic levitation has been investigated. The levitation force was investigated below 35 K. The results show that the SPS process allows to produce dense samples with enhanced superconductor characteristics as a result of improved grains connection and better densification of the bulk MgB2 superconductors, which could be a viable variant for magnetic levitation applications and/or as cryo-magnets. © 2016

YBCO bulk superconductor, prepared by top-seed floating zone under microwave heating

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Superconducting Properties of MgB2 Bulk Shaped by Spark Plasma Sintering

International audienceMgB2 bulk superconductors were shaped by Spark Plasma Sintering (SPS) process and the superconducting properties were measured. The obtained materials were 98% dense. Trapped field higher than 1.4 T was measured at 20 K. Otherwise, the possibility to use MgB2 for magnetic levitation has been investigated. The levitation force was investigated below 35 K. The results show that the SPS process allows to produce dense samples with enhanced superconductor characteristics as a result of improved grains connection and better densification of the bulk MgB2 superconductors, which could be a viable variant for magnetic levitation applications and/or as cryo-magnets. © 2016

YBCO bulk superconductor, prepared by top-seed floating zone under microwave heating

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