Effect of Fe substitution for Cu on microstructure and magnetic properties of laser floating zone (LFZ) grown Bi-2212 rods

In this paper, the laser floating zone (LFZ) technique has been used to fabricate Bi2Sr2Ca1Cu2-x Fe x O (x=0,0.01,0.03,0.05,0.1) superconducting fibers. The effects of Fe substitution on grain alignment and superconducting properties of annealed fibers were studied using SEM/EDX microanalysis in addition to phase analysis and magnetic measurements realized through XRD, M-T, and M-H loops. In the same growth conditions, higher Fe contents lead to a more compact microstructure with lower porosity but also caused the formation of poor superconducting phases followed by the decrease of T c and J cmag. No evidence of enhanced pinning capability was found in the magnetic measurements. Annealed rods indicated a weakly ferromagnetic-like behavior at relatively high doping levels.This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) in the scope of 2214 International Doctoral Research Fellowship Program. A. Sotelo and M.A. Madre acknowledge MICINN-FEDER (Project MAT2008- 00429) and DGA (Consolidated research group T12) for financial support.Peer Reviewe

Grain alignment and its relationship with superconductivity and thermal transport of Ni-substituted Bi-2212 textured rods fabricated at two different growth rates

The microstructure, grain alignment, superconducting and thermal transport properties of Ni-substituted Bi-2212 rods grown at two different speeds (15 and 30 mm h−1) through the Laser Floating Zone method, have been evaluated. Significant variations in grain size, grain alignment, electrical and thermoelectric power properties have been observed for the rods depending on the growth and substitution rates. The highest aligned structure was obtained on unsubstituted rods grown at 15 mm h−1. Both increased substitution and growth rates degraded the grain alignment. The presence of Ni-based secondary phases showed that Ni is not totally incorporated into the crystal structure, which, in turn, caused a decrease on the average grain size of the rods. With increasing Ni concentration, peak values of thermoelectric power of the rods, which lie between 3.8 and 6.4 μVK−1, monotonically decreased while thermal conductivity values did not show any systematic change. The activation energy of flux motion, Uo, was calculated from the field dependent resistivity–temperature curves in a range of 0–8 T. Superconducting transition temperatures, Tconset and Tcoffset, and activation energy, Uo, were found to decrease with increasing Ni contents and applied magnetic field. It has been estimated from the magnetic field dependence of activation energy of the samples that plastic creep of the collective vortices is dominant in the rods.This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under 2214 International Doctoral Research Fellowship Program (M. Ozabaci). A. Sotelo and M.A. Madre acknowledge DGA (Consolidated research group T12) for financial support. M. A. Madre acknowledges MINECO-FEDER (Project MAT2011-22719) for funding.Peer Reviewe

Effect of secondary annealing process on critical current density in highly textured Bi-2212 superconducting system

Bi-2212 samples prepared by a solid-state reaction technique have been grown from the melt using the laser floating zone method. After annealing the as-grown bars, the samples showed a good grain alignment and a high transport critical current density. Secondary annealing processes were performed on the annealed samples with the aim of producing Bi-2212 phase controlled decomposition. Hence, the Bi-2201 phase and the secondary phases, which act as effective pinning centers, were obtained with the secondary annealing process. After these thermal treatments, the transport critical current densities of samples significantly increased, when compared to the annealed ones. The maximum critical current density was achieved when the samples were subjected to secondary annealing at 680°C for 168 h with an improvement of ~80%, compared to the annealed ones. Moreover, it was found that magnetization of the secondarily annealed samples was also increased. The magnetic critical current densities in these secondary annealed samples were about 3 times higher than the values obtained for the annealed ones. These results clearly indicate that the secondary annealing processes lead to the formation of effective pinning centers in the bulk material.The authors acknowledge financial support from the Gobierno de Aragón (Grupos de Investigacion Consolidados T12 and T87) and the Spanish MINECO-FEDER (Project MAT2013-46505-C3-1-R).Peer Reviewe

Pharmacokinetics and clinical efficacy of midazolam in children with severe malaria and convulsions

Midazolam (MDZ), a water-soluble benzodiazepine, can be administered via several routes, including intravenously (IV), intramuscularly (IM) and buccal routes to terminate convulsions. It may be a suitable alternative to diazepam to stop convulsions in children with severe malaria, especially at peripheral healthcare facilities. The pharmacokinetics of MDZ have not been described in African children, in whom factors such as the aetiology and nutritional status may influence the pharmacokinetics. Administration of MDZ (IV, IM, or buccal) at the currently recommended dose (0.3 mg kg−1) resulted in rapid achievement of median maximum plasma concentrations of MDZ within the range 64–616 ng ml−1, with few clinically significant cardio-respiratory effects. A single dose of MDZ rapidly terminated (within 10 min) seizures in all (100%), 9/12 (75%) and 5/8 (63%) children following IV, IM and buccal administration, respectively. Although IM and buccal MDZ may be the preferred treatment for children in the pre-hospital settings the efficacy appears to be poorer

Thick film glass-ceramic superconductor fabrication

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN015225 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Structural and superconducting properties of magnetically doped Bi-2212 textured rods grown by laser floating zone (LFZ) technique

In this work, we have applied the laser floating zone technique, a well-known method to produce highly aligned crystals and dense morphology, with improved transport properties, to obtain Bi2Sr2Ca1Cu2−x Ni x O (x=0, 0.01, 0.03, 0.05 and 0.1) fibers of about 1.8 mm diameter ×12 cm length. Microstructural and magnetic properties of textured materials grown in the optimum conditions were analyzed through scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), powder XRD patterns, M–T and M–H loops. XRD analysis showed that addition of Ni at x=0.1 level caused the formation of small amounts of Bi-2201 phase. Thermal treatment has produced the agglomeration of Ni particles up to a few μm, detected by dot mapping EDX. Both T c-onset and J cmag values of the annealed rods decreased with the increasing Ni substitution rate, determined from the M–T and M–H loops, respectively.This work was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under 2214 International Doctoral Research Fellowship Program. A. Sotelo and M.A. Madre acknowledge MICINN-FEDER (Project MAT2008-00429) and DGA (Consolidated research group T12) for financial support.Peer Reviewe

Relationship between annealing time and magnetic properties in Bi-2212 textured composites

In this study, we report the physical and magnetic properties of Bi2Sr2CaCu2Ox textured materials prepared by a LFZ melting technique and annealed for different times (60, 72, 96 and 120 h). SEM images of the annealed samples for 96 and 120 hours indicate very good alignment with the longitudinal rod axis. In all cases, X-ray diffraction patterns show that the Bi-2212 phase is the major one. The magnetization measurements have been carried out as a function of the magnetic field up to 9 kOe. Jc values of the samples were calculated by using the Bean model. The results indicate that the different annealing time has no significant effects on the Tc values but, significant change on the critical current values of samples, Jc, has been obtained for sample annealed at 96 hours. We also found that the maximum critical density of Jc is 5.5 × 105 A/cm2 at 10 K for the 96 hours annealed sample.This work is supported by Research Fund of Çukurova University, Adana, Turkey, under grant contracts no: FEF2011BAP15. B. Özçelik and B. Özkurt acknowledge financial support from the Council of Higher Education (YÖK) in Turkey for international mobility. M.A. Madre and A. Sotelo acknowledge the MICINN-FEDER (Project MAT2008-00429), the Universidad de Zaragoza (Project UZ2011-TEC-03), and the Gobierno de Aragón (Consolidated research group T12) for financial support.Peer Reviewe