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La texturation de composés YBa2Cu3O7-xa été réalisée par un dispositif de fusion de zone sous champ magnétique. Un fort gradient thermique vertical, suivant lequel les échantillons sont translatés, combiné à un champ magnétique horizontal de 5 teslas permet l'alignement des cristallites avec les plans (a,b) perpendiculaires au champ et parallèles au gradient thermique du four. En champ propre et à 77 K, un courant continu de 1 000 A a circulé à travers un échantillon multigrain de 13 mm2de section et de 20 mm de longueur, prouvant la qualité des joints de grains. Des courants de 200 A ont également circulé dans H = 8 T (H ⊥I ) pour une large fenêtre d'angles entre le champ et les plans (a, b). Ces premiers résultats sont encourageants pour des applications pratiques possibles avec des barreaux texturés de grandes dimensions.

An inhomogeneous magnetic field exerts a force on magnetic materials and can be used either to compensate gravity, control convection in a magnetic liquid or modify the microstructure of a solidified multiphased system where the phases exhibit dilferent magnetic susceptibilities. A homogeneous field may produce a preferred crystallographic alignment in systems which exhibit an anisotropy of their magnetic susceptibility near their melting point. We present an experimental study of those ef[ ects, demonstrating t heir impact on the elaboration of a wide range of materials.

Thin-wall geometry implies a regular network of holes in a bulk, centimetric sample so that its effective thickness can be considered to be smaller than 1.5 mm. Thin-wall geometry offers a significant potential for helping the oxygenation process, mechanical reinforcement and thermal stabilization. Thin-wall geometry was obtained by drilling holes in slightly sintered pellets or by pressing pellets with embedded needles. The growth of a single domain, up to 50 mm in diameter, on such thin-wall geometry pellets was confirmed, despite the presence of many-hole patterns, by in situhigh-temperature video monitoring. A significant decrease of porosity and cracks is observed, associated with the reduction of diffusion paths produced by thin-wall geometry. The improvement of the material quality is established by a significant increase (about 40%) of the magnetic trapped field in thin-wall samples.

((RE)_0.33Eu_0.33Gd_0.33)Ba₂Cu₃O_y bulk superconductors (RE =  Sm, Nd) were textured by the top seeded melt textured growth method in a reduced oxygen atmosphere, so-called oxygen controlled melt growth (OCMG). Large single domains of diameter 16 mm were successfully grown. Their microstructure and their magnetic and transport properties were investigated and compared. The resistive transition was found around 88 K, which is not the optimal T_c of 95 K that could be obtained on a small re-oxygenated sample cut out from the bulk. Transport measurements were also performed on these samples at various temperature from 77 to 88 K. In the case of Nd_0.33Eu_0.33Gd_0.33Ba₂Cu₃O_y (NEG) composition, the angular dependence of the critical current densities along the (a,b) planes as a function of magnetic field was also measured. Transport critical current densities higher than 50 000 A cm⁻² are reached at 77 K and up to 2 T, corresponding to the nominal critical currents of 90 A injected through sections less than 0.25 mm² reproducibly. This confirms the high quality of the single domain obtained with a well controlled process, evidencing that mixing of rare earth is a very promising composition for transport and high-field applications.

((RE)0.33Eu0.33Gd0.33)Ba2Cu3Oybulk superconductors (RE =  Sm, Nd) were textured by the top seeded melt textured growth method in a reduced oxygen atmosphere, so-called oxygen controlled melt growth (OCMG). Large single domains of diameter 16 mm were successfully grown. Their microstructure and their magnetic and transport properties were investigated and compared. The resistive transition was found around 88 K, which is not the optimal Tcof 95 K that could be obtained on a small re-oxygenated sample cut out from the bulk. Transport measurements were also performed on these samples at various temperature from 77 to 88 K. In the case of Nd0.33Eu0.33Gd0.33Ba2Cu3Oy(NEG) composition, the angular dependence of the critical current densities along the (a,b) planes as a function of magnetic field was also measured.

Bulk Bi2212 containing 10 wt.% MgO was textured by magnetic melt processing (MMP). Hot forging (HF) applied after MMP slightly increased the critical current density (Jc). Transport Jc at 77 K was enhanced by post annealing in air and reached 1900 A/cm2 after argon annealing. The magnetization at 4 K was slightly increased by annealing in air. Using the Bean model, a Jcm of 170 kA/cm2 was calculated at 4 K. Further argon annealing decreased this value. The strong intergranular junctions obtained by MMP and HF explained the high Jcm at 4 K.

Three new thallium cuprates TlIII2 − (x3) TlI1 − xBa1 + xLnCu2O8(Ln = Pr, Nd, Sm; x = 0.25)have been isolated. The structure of these tetragonal oxides has been determined from X-ray powder data and HREM. They belong to the 2212-type Tl2Ba2CaCu2O8in which Tl(I) and Ln(III) have been substituted for Ba and Ca, respectively. A wide homogeneity range can now be predicted, involving a complex non-stoichiometry phenomenon. These oxides exhibit, like bismuth and lead cuprates, incommensurability phenomena which are attributed to the 6s2lone pair of Tl(I). The absence of superconductivity in those oxides is discussed.

3.5 GeV-Xenon ions-induced defects in Fe-doped 1.2.3 phases YBa2Cu3-xFexO7-δ with x = 1, 0.3 and 0.45 have been investigated by means of in situ resistance measurements at 100 K and Mossbauer spectroscopy at 300 K. Beside the exponential dependence of the resistance with Xe-fluence, the radiation effects result in the appearance on the Mossbauer absorption spectra of a fourth quadrupole doublet D4 (δ≈0.3 mm/s, ΔQ4 ≈ 1.1 mm/s) whose relativeintensity increases with dose i.e. with latent track density. Concerning the distribution of Fe Species on Cu sites in the unperturbed part of the sample, a strong interrelation between the variations of the relative areas of quadrupole doublets D1 (ΔQ1 ≈ 1.1 mm/s) and D3 (ΔQ3 ≈ 0.3 mm/s) under irradiation lead us to assign the corresponding Fe species substituted on Cu(1) sites ([CuO2]∞ chains of corner sharing CuO4 groups), in agreement with heat treatment analysis.

Un limiteur de courant supraconducteur pourrait être utilisé en haute tension. La plupart des matériaux à haute température critique existants actuels ont été testés en situation de limitation du courant. Les matériaux massifs sont classés par densité de courant critique croissante qui correspondent à des comportements différents. Le champ critique lors des transitions semble être de l'ordre de 1 kV/m.

Afin de déterminer la capacité à limiter le courant du composé ${\rm Y}_1{\rm Ba}_2{\rm Cu}_3{\rm O}_{7-\delta}$texturé, des études en courants de transport élevés, en régime pulsé et en régime permanent alternatif, ont été menées. Il en résulte que YBaCuO possède une forte capacité de transport du courant en régime pulsé (9000 A soit 23 000 $\ {\rm A} / {\rm cm}^2$dans un barreau de 4 cm de long) et en régime permanent alternatif (3000 A soit 7800 $\ {\rm A} / {\rm cm}^2$) et que le retour à l'état normal par dépassement du courant critique est très abrupt.

Des forts courants pulsés d'une durée comprise entre 1,25 et 20 ms ont été appliqués à T= 77 K à des conducteurs Bi:2223 texturés par forgeage à chaud ou frittés. Pour des pulses de courant ${I>I_{\rm c}}$, deux comportements sont observés : quand la température moyenne de l'échantillon est inférieur à ${T_{\rm c}}$, le matériau retourne dans l'état supraconducteur avant la fin du pulse de courant. Au dessus de ${T_{\rm c}}$, l'échantillon transite dans l'état normal après le pulse de courant à cause de l'élévation de température. Ceci induit une puissance instantanée importante appliquée au conducteur de 182 GW/m3. À I = 15Ic, des champs électriques de 400 à 1000 V/m sont obtenus sur des éléments frittés et texturés.

We study the limitation possibilities of bulk Bi high Tcmaterials. For this we test these materials with a.c. or d.c. currents above their critical currents. We study particularly the evolution of the voltage with time or with current. The material, the value of the current and the time duration play important parts. For sintered Bi samples the voltage depends only on the current even for values much larger than the critical current. With textured samples the V(I) curves shows an hysteretic behaviour due to a warming up. The textured materials are more interesting than sintered ones in terms of required volume for the current limitation. In both cases the superconductors are in a dissipative state but not in the normal state. This state is nevertheless reached if the dissipated energy inside the sample is sufficient. We have tried to apply a magnetic field on the samples in order to trigger a more effective limitation. The voltage increases but with a limited effect for currents much higher (3–4 times) than the critical zero field current. We think that the dissipative state is due mainly to the grain boundaries which become resistive above the critical current.

Texturing of high-temperature superconducting ceramics leads to an improved intergranular coupling. This is demonstrated on the basis of ac susceptibility measurements obtained when texturing Bi-2223 polycrystals through combined magnetic melt texturing and hot pressing (MMTHP) and Y123 bulk samples obtained through combined magnetic melt texturing and zone melting (MMTZM).

Industrial applications of the bulk superconducting YBa2Cu3O7material imply to control the growth of large oriented monodomains in samples of big size (several centimeters). The laboratory EPM-Matformag is committed to produce such materials according to three different methods (zone melting, solidification controlled by a magnetic field, crystal growth from a seed). The results obtained show that it is possible by such methods to elaborate a material with high performances at the centimeter scale and to produce it in series. The availability of such materials allows the measure of physical properties on a large scale and the testing of prototypes for cryo-electrotechnical applications (magnetic bearing, flywheel, coupling device, current lead...).

The "1212"-type oxide TIBa2NdCu2O7 has been investigated by high resolution electron microscopy in order to shed more light on the problem of extended defects in these structures. Besides the classical intergrowth defects involving rock salt and perovskite layers, original defects characterized by the presence of double fluorite-type layers have been observed. The latter defects open the route to the synthesis of new families of superconductive cuprates, corresponding to the intergrowth of the three structures: perovskite. rock-salt type and fluorite.

This paper demonstrates that, by taking advantage of the anisotropy in the paramagnetic susceptibility of the high-temperature superconducting oxide YBa2Cu3O7-δ it is possible to prepare bulk textured samples of this material by solidification in a magnetic field. The effects of increasing the annealing temperature employed, varying the strength of the annealing field and altering the temperature range in which an annealing field is applied on the properties of the material obtained are discussed.

La densité de courant critique selon l'axe c(Jc) est mesurée à 77 K en transport et par des mesures magnétiques sur les mêmes échantillons texturés monodomaines d'YBaCuO. L'influence des plans de macles (TP) sur Jcet sur la ligne d'irréversibilité $B(T^*$) est étudiée en faisant tourner le champ dans les plans ab, perpendiculairement à l'axe c. Les résultats montrent que dans ces composés, Jcet $B(T^*$) sont fortement influencés par le piégeage par les TP. Divers comportements des lignes de flux résultant de l'influence de ces défauts corrélés sont proposés selon les gammes de température et de champ étudiées.

Bulk magnetically melt textured YBaCuO at 77 K shows critical current densities of up to 19000 A/cm2 in 20 teslas when the field is parallel to the(a, b) planes. The angular dependence ofJc is shown to support a recent interpretation of the high superconducting transport currents measured above the irreversibility line in terms of intrinsic surface superconductivity. The behavior when the field is applied very close to the(a, b) planes is shown to follow a two dimensional model meaning that the maximum current density is determined by thec-axis component of the applied field. The size and density of 211 inclusions are probably the main factors which determines the maximum critical current density.

Abstract: We have measured dc transport critical current densities of melt texture grown and magnetically melt textured bulk YBaCuO at 77 K and in magnetic field. A maximum value of over 31,000 A/cm2 is obtained with a field of 7 teslas applied parallel to the (a, b) planes. Over the rest of the angular range the critical current is shown to be determined mainly by thec-axis component of the applied field. Although this dependency is expected in the presence of two-dimensional vortices, in fact the data are shown to correspond better to the behavior expected of an anisotropic three-dimensional superconductor. These results are compared to magnetization measurements on the same samples. We show that when the field is directed close to the c-axis, superconducting transport currents flow at fields well above the field at which the irreversible magnetization disappears.

Texturation of YBa2Cu3O7-xhas been achieved in a zone melting apparatus in a magnetic field. A strong vertical thermal gradient, along which samples are pulled ; combined with a horizontal magnetic field of 5?teslas induces cristallite alignment with their (a,b) planes perpendicular to the magnetic field and parallel to the thermal gradient. At H = 0 T and T = 77?K, a dc current of 1?000?A passed through a multigrain sample of 13?mm2section and 20?mm length, thus proving the quality of grain boundaries. 200?A currents also passed through in H = 8 T (H ?I ) for a large angular range between H and (a,b) planes. These preliminary results are encouraging for possible practical applications of large sized textured bar samples. La texturation de compos?s YBa2Cu3O7-xa ?t? r?alis?e par un dispositif de fusion de zone sous champ magn?tique. Un fort gradient thermique vertical, suivant lequel les ?chantillons sont translat?s, combin? ? un champ magn?tique horizontal de 5?teslas permet l'alignement des cristallites avec les plans (a,b) perpendiculaires au champ et parall?les au gradient thermique du four. En champ propre et ? 77?K, un courant continu de 1?000?A a circul? ? travers un ?chantillon multigrain de 13?mm2de section et de 20?mm de longueur, prouvant la qualit? des joints de grains. Des courants de 200?A ont ?galement circul? dans H = 8 T (H ?I ) pour une large fen?tre d'angles entre le champ et les plans (a, b). Ces premiers r?sultats sont encourageants pour des applications pratiques possibles avec des barreaux textur?s de grandes dimensions.

An inhomogeneous magnetic field exerts a force on magnetic materials and can be used either to compensate gravity, control convection in a magnetic liquid or modify the microstructure of a solidified multiphased system where the phases exhibit dilferent magnetic susceptibilities. A homogeneous field may produce a preferred crystallographic alignment in systems which exhibit an anisotropy of their magnetic susceptibility near their melting point. We present an experimental study of those ef[ ects, demonstrating t heir impact on the elaboration of a wide range of materials.

Y1Ba2Cu3O7-dtextured by the melting zone technique and by the MTG technique have been studied at high transport currents. Pulsed transport currents reaching values of 8000A (20 000A/cm2) could cross samples of several centimeters in length at 77K. The self-field losses in high current are low even in samples of 5 or 7 mm diamter and the transition to the normal state is very abrupt which is highly desirable for current limitation applications.

High pulsed currents attaining 3300 A with a duration varying from 1.25 to 20 milliseconds have been applied at 77 K to sintered Bi1.8Pb0.4Sr2Ca2.2Cu3O10.3+xlong bars. Measurements of voltage versus applied current determine the critical current Ic = 60 A, and the conditions for superconductivity recovery. Two types of behaviour are observed: (i) When the mean temperature T raises up to T < 95 K a critical current is recovered at the end of the pulse. (ii) When the temperature goes beyond 95 K, Ic goes to zero after the pulse. The temperature increases up to 43 K for a 20 ms pulse. No deterioration in the sample is observed and experiments can be reproducibly repeated. Voltages as high as 90 V have been measured, corresponding to an electrical field of 1100 V/m. The maximum instantaneous power applied to the material is 180 GW/m3and the maximum energy per unit volume transmitted to the sample after a 20 ms pulse is 75 MJ/m3.

We report the synthesis of the “high pressure” tetragonal form of Sr2CuO3+xby direct reaction of stoichiometric mixtures of oxide, peroxide or carbonate of strontium and copper oxide intimately grounded in a ball mill for long periods of time. We present thermogravimetric analysis. We have determined that this phase can be obtained in the temperature range between 350 to 450°C. Above this temperature the orthorhombic structure is more stable. All the obtained samples are non-superconducting in contrast to the high-pressure obtained samples.

The pinning of flux lines by the twin planes is studied in bulk textured YBCO single domains using magnetic field angular measurements of c-axis critical current density Jc(Φ). Above a matching field BMassociated with the twin boundary network, Jc(Φ) shows a fourfold peak structure related to the pinning by each variant of the twin plane (TP). Below BM, Jcis angular and field independent, which is consistent with a complete adaptation of the flux lines to the twin planes network. In the direction of the TP, Jcis independent of the field intensity up to 8 T suggesting that twin plane pinning might have a magnetic origin in addition to the core pinning effect.

Turbulence and nitrate measurements collected in the Amundsen Gulf during ice‐covered conditions in fall 2007 are combined to provide mean vertical profiles of eddy diffusivity and diffusive nitrate fluxes . The mean diffusivity (with 95% confidence intervals) was maximum near the uppermost sampling depth (10 m) with max= 3(2, 5) × 10−3m2s−1and decreased exponentially to a depth of ∼50 m, below which it was roughly constant at the background value b= 3(2, 5) × 10−6m2s−1. The nitracline, centered around 62 m depth, was subject to an eddy diffusivity close to the background value band the mean diffusive nitrate flux across the nitracline was nit= 0.12(0.075, 0.20) mmol m−2d−1. These observations are compared with other regions and the role of vertical mixing on primary production in the Amundsen Gulf is discussed. The average turbulent nitrate flux through the nitracline was 0.5 mmol/m3/dParameterization for the depth‐dependence of the turbulent diffusivity is givenTurbulent mixing may have contributed to 60% of total nitrate uptake