Characterization of the Intra-Unit-Cell magnetic order in Bi2Sr2CaCu2O8+d

As in YBa2Cu3O6+x and HgBa2CuO8+d, the pseudo-gap state in Bi2Sr2CaCu2O8+d is characterized by the existence of an intra-unit-cell magnetic order revealed by polarized neutron scattering technique. We report here a supplementary set of polarized neutron scattering measurements for which the direction of the magnetic moment is determined and the magnetic intensity is calibrated in absolute units. The new data allow a close comparison between bilayer systems YBa2Cu3O6+x and Bi2Sr2CaCu2O8+d and rise important questions concerning the range of the magnetic correlations and the role of disorder around optimal doping.Comment: 12 pages, 8 figures, submitted to physical review

Melt processing of (light rare earth) Ba 2 Cu 3 O y materials by the floating zone method

International audienceThe floating zone method has been optimized to process the (light rare earth) Ba2Cu3Oy (LRE123) compound. The effects of processing rate, thermal gradient and maximal temperature have been investigated. Nd1Ba2Cu3Oy, Sm1Ba2Cu3Oy, Gd1Ba2Cu3Oy and (Nd0.33Eu0.33Gd0.33)1Ba2Cu3Oy have been processed under air and exhibited an optimal critical temperature greater than 93 K with a sharp transition. Critical current densities under self-field of 55000 A cm−2 have been reached and a fishtail effect appears under 2 T with different mixing of light rare earth. Large single domains have been obtained with the (a, b) plane oriented at 90° of the bar axis. Moreover, the composition homogeneity has been tested along the Nd123 bar. Thus, the floating zone method is an interesting process to investigate under air new compositions of LRE123

Melt processing of (light rare earth) Ba 2 Cu 3 O y materials by the floating zone method

International audienceThe floating zone method has been optimized to process the (light rare earth) Ba2Cu3Oy (LRE123) compound. The effects of processing rate, thermal gradient and maximal temperature have been investigated. Nd1Ba2Cu3Oy, Sm1Ba2Cu3Oy, Gd1Ba2Cu3Oy and (Nd0.33Eu0.33Gd0.33)1Ba2Cu3Oy have been processed under air and exhibited an optimal critical temperature greater than 93 K with a sharp transition. Critical current densities under self-field of 55000 A cm−2 have been reached and a fishtail effect appears under 2 T with different mixing of light rare earth. Large single domains have been obtained with the (a, b) plane oriented at 90° of the bar axis. Moreover, the composition homogeneity has been tested along the Nd123 bar. Thus, the floating zone method is an interesting process to investigate under air new compositions of LRE123

Microstructure and superconducting properties of top-seeded melt grown YBa 2 Cu 3 O 7 bulks doped with BaF 2

The effects of fluorine on superconducting properties and microstructures of top-seeded melt grown YBa2Cu3O7−δ bulks have been investigated through BaF2 additions (up to 1 wt% BaF2). DTA measurements show that the decomposition temperature is lowered when the content of BaF2 is increased (1003 °C for the sample doped with 1 wt% BaF2). The microstructures of the doped samples are similar to those observed in fluorine-free samples. In particular, a negligible effect is observed on the size of the Y211 particles. In the same way, the superconducting properties do not change with the additions of BaF2. DTA measurements of heavily doped compositions (up to 10 wt% BaF2) show that the decomposition temperature is lowered down to 969 °C for an addition of 5 wt% BaF2. This makes BaF2 additions promising to replace silver additions in welding processes

Influence of composition on morphology of semiconducting oxides microwires

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Texturation of NdBa2Cu3Oy bars under air in a vertical Bridgman furnace

International audienceNd123 bars were textured using the melt texturing growth process in a vertical furnace by the floating zone method. Different applied growth rates were tested, from 1 to 4 mm/h, combined with different secondary phases additions (Nd4Ba2Cu2O5 and Nd3.6Ba2.2Cu1.9Oy). Nd123 single-domains were obtained independently of the tested conditions and correlation between process conditions (composition, growth rate), microstructure and superconducting properties were investigated. An optimized Tc (96 K) with a sharp transition is obtained without Ar annealing at high temperature generally necessary to recover the optimal Tc. This attractive result is linked with the process used. Jc curves were measured and results were discussed in relation with process conditions

Qualitative and quantitative analysis of twin structure in top seeding melt texture growth-processed YBa

The present study reviews the techniques suitable for twin characterisation in TSMTG-processed ceramics: Conventional Transmission Electron Microscopy, Scanning Electron Microscopy (backscattered electrons images), and X-ray diffraction (pole figures). Optical microscopy can not be used because twin spacing in the studied ceramics are smaller than this technique resolution. A difference between SEM looking like twins average spacing and TEM twins average spacing is pointed out and some explanations are envisaged. Concerning X-ray diffraction, rocking curves can not be used to characterise twins in textured ceramics, but pole figures allow qualitative measurements

Investigation to obtain long Y123 textured bars by vertical MTG process

International audienceThe floating zone method is currently used to obtain Y123 melt textured bars, however the final sample length is always limited by the sample lower part weight which is sustained only by the liquid phase tension surface energy. Indeed, the basic scheme is to attach the bar only by the upper part and the lower part is totally free. A vertical furnace permits then to heat locally the bar and to create the floating zone. The sample translation at low speed (about 1 mm/h) allows the formation of a re-crystallization zone, according to the well known reaction Y211+Liquid (Ba and Cu rich) --> Y123, permitting the fabrication of a well textured bar. This work is devoted to present a modification of this process in order to have no limitation in the sample length. The idea which is developed here is to include inside the bar and co-axially a platinum wire. We have chosen a platinum wire due to its high melting temperature and its relatively low reactivity with Y123. We present here results obtained in term of reactivity, texture formation and superconducting properties when Y123 is textured in the presence of platinum wire versus different doped element introduced in the initial mixture

Ca doping of TSMTG-YBa2Cu3O7−δ/Y2BaCuO5 composites

International audienceCalcium doped YBa2Cu3O7−δ/Y2BaCuO5 bulk samples have been synthesised by the top-seeding-melt-texture growth (TSMTG) process up to 1 wt.% of CaCO3. Calcium additions up to 0.25 wt.% of CaCO3 do not change the decomposition temperature whereas additions of 1 wt.% of CaCO3 lead to an increase of the decomposition temperature of about 10 °C. This difference is not important enough to change the thermal cycle used to process YBa2Cu3O7−δ undoped bulk samples. Microstructure studies show that no precursor or secondary phases containing calcium are present in the samples. Energy dispersive spectroscopy analyses have shown that Ca is present both in the YBa2Cu3O7−δ matrix and the Y2BaCuO5 particles. The position of the calcium atoms in the superconducting matrix is discussed. The calcium doped samples present slightly depressed critical temperatures but drastically depressed critical current densities

Texturation of NdBa2Cu3Oy bars under air in a vertical Bridgman furnace

International audienceNd123 bars were textured using the melt texturing growth process in a vertical furnace by the floating zone method. Different applied growth rates were tested, from 1 to 4 mm/h, combined with different secondary phases additions (Nd4Ba2Cu2O5 and Nd3.6Ba2.2Cu1.9Oy). Nd123 single-domains were obtained independently of the tested conditions and correlation between process conditions (composition, growth rate), microstructure and superconducting properties were investigated. An optimized Tc (96 K) with a sharp transition is obtained without Ar annealing at high temperature generally necessary to recover the optimal Tc. This attractive result is linked with the process used. Jc curves were measured and results were discussed in relation with process conditions