1,747,742 research outputs found
The development of high field magnets utilizing Bi-2212 wind & react insert coils
No full textWind & react Bi-2212 inserts have been manufactured and tested inside a wide-bore NbTi-Nb3Sn magnet providing a background field up to 20T at 4.2K. A pair of six-layer concentric coils both achieved critical currents of 350 A (JE = 200 A/mm2) in a 20T background field. A thicker 14-layer insert made from 119m of round wire had a critical quench current IQ of 287A (JE = 162 A/mm2) at the same field and contributed to a combined central field of 22.5 T. This is a record for a fully superconducting magnet at 4.2 K. The 14-layer coil, equipped with an external protective shunt, was used for an extensive series of quench measurements and endured >150 quenches without damage. Minimum quench energies were found to be in the range of 200-500mJ in background fields of 15-20T when the coil carried 70-95% of its critical quench current
Superconducting joints of Bi-2212/Ag tapes and laminates
No full textDifferent types of HTS joints of Bi-2212/Ag tapes and laminates, which are fabricated by dip-coating and partial-melt processes, have been investigated. All joints are prepared using green single and laminated tapes and according to the scheme: coating-joining-processing. The heat treated tapes have critical current (Ic) between 7 and 27 A, depending on tape thickness and the number of Bi-2212 ceramic layers in laminated tapes. It is found that the current transport properties of joints depend on the type of laminate, joint configuration and joint treatment, Ic losses in joints of Bi-2212 tapes and laminates are attributed to defects in their structure, such as pores, secondary phases and misalignment of Bi-2212 grains near the Ag edges. By optimizing joint configuration, current transmission up to 100% is achieved for both single tapes and laminated tapes
Bi-2212/Ag laminated tapes: Bending and joining effects
No full textSuperconducting composite Bi-2212/Ag tapes and their joints are fabricated by a combination of dip-coating and partial melt processing. The heat treated tapes have a critical current (Ic) between 8 and 26A, depending on tape thickness and the number of Bi-2212 layers. Current transmissions between 80% and 100% have been achieved through the joints of tapes. Different types of HTS joints of Bi-2212/Ag laminated tapes are made and their transport properties during winding operations are investigated. Irreversible strain values (ε irrev) for laminated tapes and their joints are determined and it is found that the degradation of Ic during tape bending depends on the type of joint
Angle-Resolved Photoemission Studies on the Many-Body Effects of High-Temperature Superconductor: Bi-2212
No full textSpin fluctuations are defined as dynamic variations of spin density in both space and time. They are widely considered to play a essential role in the pairing mechanism of high temperature superconductors. Unconventional superconductors such as cuprates are believed to exhibit spin-fluctuation-mediated pairing, as opposed to conventional superconductors where phonons mediate Cooper pairing. Dynamic spin susceptibility can characterize these fluctuations. It describes the magnetic response of the system to perturbations. The imaginary part of this function captures the full spectrum of spin excitations in both the normal and superconducting states. It can be typically measured via inelastic neutron scattering (INS). However, such measurements for Bi-2212 are rare because of small scattering cross-sections and difficulties in growing sufficiently large crystals. In this work, we developed a stable photon-energy helium lamp–based ARPES (angle-resolved photoemission spectroscopy) system with high energy resolution to extract detailed single-particle spectral functions in Bi-2212. Using these spectral functions, we reconstructed both the non-interacting and interacting spin susceptibilities in the normal and superconducting states. The ARPES-derived susceptibilities reveal a broad continuum of spin excitations in the normal state and a sharp spin resonance emerging in the superconducting state due to the collective spin-1 excitation. These results reflect the underlying correlated electron dynamics in Bi-2212 and support the picture of spin fluctuations as a key mediator of high temperature superconductors
Zr, Hf, Mo and W-containing oxide phases as pinning additives in Bi-2212 superconductor
No full textZr, Hf, Mo and W-containing oxide phases as pinning additives in Bi-2212 superconductor
M.V. Makarova, Corresponding Author Contact Information, E-mail The Corresponding Author, P.E. Kazin, Yu.D. Tretyakov, M. Jansen, M. Reissner next term and W. Steiner
Chemistry Department, Moscow State University, Leninskie gori, 119992 Moscow, Russia
Max-Plank-Institute für Festkörperforschung, D-70569 Stuttgart, Germany
Vienna University of Technology, Wiedner Hauptstraβe 8-10, A-1040 Vienna, Austria
Received 7 April 2004; revised 30 November 2004; accepted 7 December 2004. Available online 30 December 2004.
Abstract
Phase formation was investigated in Bi-Sr-Ca-Cu-M-O (M = Mo, W) systems at 850-900 °C. It was found that Sr2CaMO6 phases were chemically compatible with Bi-2212. The composites Bi-2212-Sr2CaMO6 and Bi-2212-SrAO3 (A = Zr, Hf) were obtained from a sol-gel precursor using crystallisation from the melt. The materials consisted of Bi-2212 matrix and submicron or micron grains of the corresponding dispersed phase. Tc was equal or exceeded that for undoped Bi-2212, reaching Tc = 97 K in the Mo-containing composite. The composites exhibited enhanced pinning in comparison with similar prepared pure Bi-2212, especially at T = 60 K. The best pinning parameters were observed for the Bi-2212-Sr2CaWO6 composite
Bi-2212/Ag tapes and laminates : effects of bending
No full textSuperconducting Bi-2212 tapes and laminates are fabricated by a combination of dip-coating and partial melt processing. The heat treated tapes have critical current densities (Jc) up to 11 kAcm -2. We investigate the degradation of critical current (Ic) during bending experiments for both single tapes and tapes with laminate structure. Although degradation of Ic is observed in both forms, the characteristics of the degradation differ. It is determined that laminated tapes perform better than single tapes when critical current is measured against bending radius, and laminated tapes tolerate a higher strain for a given reduction in critical current. It is found that increasing the number of Bi-2212 layers increases the total Ic of the laminated tape, but degradation of critical current is more pronounced during bending because of the increased total thickness of the laminate structure. It is also found that addition of silver to the Bi-2212 layers reduces critical current degradation during bending for both tapes and laminates
XPS Studies of Single Crystals of Bi-2212, Tl-2212 and Tl-2223
No full textHigh quality single crystals of Bi-2212, Tl-2212 and Tl-2223 were studied using X-ray photoelectron
spectroscopy. From a deconvolution of the Cu2p3/2 main line, we have shown that the density of O 2p holes in the Cu-O
planes are qualitatively similar in case of the Bi and Tl-2212 systems even though they have shown many other differences
in their electronic structure properties. Also the results show a dependence of the density of holes on the number of Cu-O
planes as we go from Tl-2212 to Tl-2223
MAGNETIC MEASUREMENTS ON TL-2212 AND BI-2212 SINGLE-CRYSTALS - A COMPARATIVE-STUDY
No full textWe have compared the magnetic behaviour of two identicaly shaped single crystals, Tl2Ba2CaCu2O8 and Bi2Sr2CaCu2O8. The critical current density is found to decrease more rapidly with temperature in Bi-2212 although it is the highest in this material at low temperatures (T < 20K). I-V characteristic curves have been obtained from measurements of magnetic sweep rate dependencies of the hysteresis loops. We have found that the characteristic temperature at which flux motion becomes important is significantly higher in Tl-2212 than in Bi-2212. Hence the Tl-2212 has a larger effective pinning
Methods of introduction of MgO nanoparticles into Bi-2212/Ag tapes.
No full textThe effect of addition of ultra-fine MgO particles, obtained by Mg combustion, in Bi-2212/Ag tapes was investigated. Bi-2212/Ag tapes were prepared by coating and partial melt processing. Four different methods of MgO particles embedment were applied in green tape preparation; settlement of MgO in Bi-2212, pre-mixing of MgO in the solvent, deposition of the MgO into the solvent, and deposition of MgO onto the surface of Bi-2212. Microstructural studies of processed tapes show that uniformity of MgO particles distribution in Bi-2212 matrix depends on the methods of tape preparation. MgO particles, introduced in Bi-2212 matrix by all applied methods, significantly enhanced transport properties of the tapes. The Jc degradation with the increase of magnetic field and/or temperature in all doped samples was significantly lower compared to un-doped Bi-2212 samples. The best improvement was achieved when MgO particles were introduced into Bi-2212 matrix by settlement method of the tape coating. The improvement also depends on a magnitude of the magnetic field and operating temperatures.Griffith Sciences, Griffith School of EngineeringFull Tex
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