Abstract:
We have presented here the results of SEM and STM/STS investigations carried out on MgB2 superconductor. The
SEM pictures show porous surface and well-linked granular structure in which bigger grains (few micrometer size) seem
to be agglomeration of smaller, nearly hexagonal grains (size nearly 100 nm). Hexagonal structure of Mg and B layers
have been directly observed in atomically resolved STM images. The lattice constants have been determined to be
aMg ¼ 3:1 AA, aB ¼ 1:7 AA and c ¼ 3:5 AA. Grain boundaries (GB) of width ranging from 50 to 200 AA have been observed.
Absence of weak link effects despite wide GBs has been attributed to the metallic nature of the amorphous region of the
GB interior as inferred from STS analysis. Irradiation with 200 MeV 107Ag ions gives tracks of about 65 AA in the bulk of
the sample. This is expected to give higher value of critical current density owing to the flux pinning mechanism, which
is related to possibility of wide practical application of this material.
