Phase formation in Cu-sheathed MgB2 wires
نویسندگان
چکیده
The phases in Cu sheathed MgB2 wires fabricated using very short annealing time are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and critical current (Ic) measurements. By comparison with the XRD pattern of our synthesized MgCu2, the XRD line located at 2h 36.1 for all Cu-sheathed MgB2 wire samples is unambiguously identified to be due to the MgCu2 phase. This line was previously unidentifiable due to its absence in the standard pattern of MgCu2 recorded in the current powder diffraction file (PDF) database. We found that the XRD lines previously attributed to Cu atoms by other groups, are actually due to the CuMgd (with d 6%) phase, indicating that copper does not exist in the form of un-reacted atoms in the core materials of these Cu-sheath MgB2 wires. For samples heat treated at 700 C or below, the phases are basically the superconducting MgB2 and impurity MgCu2 phases. Quantitative analysis indicates that the molar percent of the MgB2 phase in these samples is over 90%. For samples heat treated at 725 C or above, two additional phases, CuMgd and MgB4 phases, are also present. The content of CuMgd phase increases rapidly with the increase of the heat treatment temperature from 725 C and 750 C. This increase in CuMgd content is one of the factors responsible for the dramatic decrease of Ic. These phase identification results are consistent with our SEM result and the published Cu–Mg phase diagram. It is also found that the variation of the MgB2 fraction with the heat treatment temperature peaks at 700 C, well correlated to the variation trend of Ic with heat treatment temperature. 2006 Elsevier B.V. All rights reserved. PACS: 74.70.Ad; 61.10.Nz; 74.62.Bf; 74.70. b; 74.25.Sv
منابع مشابه
پیشرفتهای اخیر در زمینه ساخت سیم و نوار ابررسانای MgB2
MgB2 wire and tape were prepared using the powder in tube and reaction in-situ technique. All samples were characterized using the XRD, SEM, TEM, as well as transport and magnetic measurements. High transport and magnetic critical current density values have been obtained for metal-clad wires and tapes. Different sheath materials have been examined, but Fe appears to be the best sheath for MgB...
متن کاملNew Method for the Fabrication of Al-Stabilized Fe/MgB2 Wires
To employ Al stabilizer on Fe sheathed MgB2 wire the hot aluminizing technique was used. The present technique allows us to form MgB2 superconductor by an in-situ reaction technique and apply Al stabilizer simultaneously, because the processing temperature of MgB2 is similar to the melting temperature of Al. Two types of Fe sheathed MgB2 wires—“reacted” and “green” (unreacted)—were immersed in ...
متن کاملIn situ investigations of phase transformations in Fe - sheathed MgB 2 wires
The phase evolution inside Fe-sheathed wires containing precursor powders consisting of a mixture of Mg and B has been studied in situ by means of x-ray diffraction with hard synchrotron radiation (90 keV). Mg was found to disappear progressively during the heating stage. At 500 ◦C, the intensity of the Mg diffraction lines is reduced by about 20%. This effect is partly attributable to MgO form...
متن کاملTHE COMBINED INFLUENCE OF SiC AND RARE-EARTH OXIDES DOPING ON SUPERCONDUCTING PROPERTIES OF MgB2 WIRES
Ti-sheathed MgB2 wires doped with different amount of nanosized rare-earth oxide (Yb2O3, Gd2O3, and Dy2O3) and/or nanosized SiC were investigated. X-ray diffraction patterns suggested the existence of Mg2Si phase due to the SiC addition, while no any phase related to rare-earth oxide could be detected. Strong enhancement of in-field current carrying capability was observed on 2.5 wt.% Yb2O3 dop...
متن کاملLarge transport Jc in Cu-sheathed Sr0.6K0.4Fe2As2 superconducting tape conductors
Copper sheath is the first choice for manufacturing high-T(c) superconducting wires and tapes because of its high electrical and thermal conductivities, low-cost and good mechanical properties. However, Cu can easily react with superconducting cores, such as BSCCO, MgB2 and pnictides, and therefore drastically decrease the transport J(c). Here, we report the fabrication of Cu-sheathed Sr(1-x)K(...
متن کامل