Quantitative phase analyses were performed on Fe-sheathed ex situ MgB2 tapes after the deformation process and after annealing at 700, 850 or 920C in vacuum. The techniques used were X-ray diffraction, differential thermal analysis and scanning electron microscopy. All of the superconducting cores were found to contain certain amounts of MgO, the largest amounts being observed near to the sheath, and after annealing at the highest temperature. Small amounts of MgB4 were detected in the inner part of the core, presumably formed by the decomposition of MgB2. At the MgB2/Fe interface, a reaction layer was observed, which was identified as being Fe2B. In addition, tapes annealed at 700C revealed the presence of the metastable phase, Fe23B6. The interaction of the MgB2 filament with the Fe sheath and the presence of trapped O limited the possibilities of current tape-fabrication techniques.

Quantitative Study of the Inhomogeneous Distribution of Phases in Fe-Sheathed ex situ MgB2 Tapes. P.Lezza, R.Gladyshevskii, H.L.Suo, R.Flükiger: Superconductor Science and Technology, 2005, 18, 753-7