Tapes were prepared by using the powder-in-tube technique. After the cold working typically carried out by wire drawing and cold rolling, it had been found that a final sintering step carried out in an Ar atmosphere was a key process for further improving the superconducting properties of the conductors. In order to study the effect of the deformation and heat treatment processes, neutron scattering experiment were performed. Due to the high penetration depth of neutron inside matter, it was possible to analyze the MgB2 phase still wrapped in the Ni sheath. The studies were carried out via full-spectra refinement using the Rietveld method. A large Mg deficiency was observed in the starting superconducting powder. In the tapes, it was found that the large forces applied during cold working induced a large MgB2 lattice deformation, and that it was partly relaxed during final sintering. An important correlation of the residual stress with the critical temperature and the pinning properties was pointed out. The appearance of detrimental secondary phases during the sintering process was also observed. In particular, the MgB2 phase reacted with the Ni sheath, and MgB2Ni2.5 was formed at temperatures higher than 850C.

Neutron Scattering Studies of Superconducting MgB2 Tapes. E.Bellingeri, A.Malagoli, M.Modica, V.Braccini, A.S.Siri, G.Grasso: Superconductor Science and Technology, 2003, 16, 276-80