Hexagonal plate-shaped MgB2 crystals were prepared at ambient pressure. A superconducting transition was observed at 37K, with a large transition width of ΔTC~22K. The lattice strain (0.7%) was calculated from the FWHM of XRD data. Both an edge dislocation with Burgers vector, b = -a, and a Mg (nano-agglomerate) self-ordering superstructure with lattice constant 2a0 were directly detected in the [001]

direction by high-resolution transmission electron microscopy. It was proposed that the very broad transition might be caused by these defects in the crystals.

Edge Dislocation and Superstructure in MgB2 Superconducting Crystals. W.Du, H.Zhang, D.Xu, X.Wang, X.Hou, G.Zhang, Y.Geng, H.Liu, F.Jiang, Y.Wang: Superconductor Science and Technology, 2005, 18, 1513-6