Anisotropic grain connectivity in shock consolidated MgB2bulk samples

We consolidated commercial MgB2 powders by two different shock consolidation methods: the single-stage propellant gun method and the underwater shock consolidation method. The samples prepared had anisotropic resistance–temperature features; the narrowest resistive transition width was observed along the directions of shock loading. In contrast, onset temperatures were independent of the directions and methods. No grain orientation previously observed would have resulted from the consolidation processes with a very short duration of . The samples showed higher diamagnetism than a cold isostatic pressed (CIPed) sample at a low field of 1 Oe. However, their diamagnetism relatively degraded with increasing fields and eventually became much less than even that of the CIPed sample. This is due possibly to thick, much distorted grain boundaries that would have behaved as weak links at high fields.