The results of various transport experiments on Mg1-xB2 indicated a surprising effect that was associated with the presence of a Mg deficiency in MgB2. This was a phase separation between Mg-vacancy rich and Mg-vacancy poor phases. The Mg-vacancy poor phase was superconducting, but the insulating nature of the Mg-vacancy rich phase probably arose from Anderson (disorder-induced) localization of itinerant carriers. Furthermore, electron diffraction measurements indicated that, within vacancy-rich regions, these defects tended to order into intriguing patterns.

Percolative Superconductivity in Mg1-xB2. P.A.Sharma, N.Hur, Y.Horibe, C.H.Chen, B.G.Kim, S.Guha, M.Z.Cieplak, S.W.Cheong: Physical Review Letters, 2002, 89[16], 167003 (3pp)