A series of Fe-sheathed superconducting wires was prepared, using the powder-in-tube technique, from (MgB2)1-x(Mg+2B)x initial powder mixtures in various proportions; such that x varied from 0 to 1. It was found that ex situ prepared wire (x = 0) had considerable disadvantages when compared with all the other wires in which in situ assisted (0 < x < 1) or pure in situ (x = 1) preparation was used. This was due to a weaker inter-grain connectivity. As a result, higher critical current densities JC were measured over the entire range of applied magnetic fields Ba for all the samples with x > 0. Pinning of vortices in MgB2 wires was shown to be due to grain boundaries. The JC(Ba) behavior was governed by an interplay between the transparency of grain boundaries and the number of pinning grain boundaries. Differences between thermomagnetic flux-jump instabilities in the samples and a possible threat to practical applications were also considered.

Properties of Superconducting MgB2 Wires - in situ versus ex situ Reaction Technique. A.V.Pan, S.Zhou, H.Liu, S.Dou: Superconductor Science and Technology, 2003, 16, 639-44