The Study On The Effect Of Carbon On The Electr Onic Structure Of The Superconducting Magnesi Um Diboride (Mgb2) By

Abstract

Experimental study results show an exceptionally large superconducting transition temperature of 39 K in MgB2. In order to understand the unexpected superconducting behavior of this compound we have made electronic structure calculations for MgB2 and closely related systems, MgB2C and MgBC. The compounds have hexagonal structures as seen by Xcrysden. Were produced the electronic band structure of pure magnesium diboride and also its density of state. We also calculated and determined the crystal structure, electronic band structure and density of state by carbon substitution in the absence of one boron, that means MgBC and by adding carbon in the in the presence of two boron, MgB2C. In both cases we determined the crystal structure, electronic band structure and density of state along high symmetry lines, using density functional theory as implemented by a code quantum –ESPRESSO. We found that, hole bands are changing around a Fermi level, except, points incase of MgB2, the hole bands are drop around the Fermi level in case of MgBC, and the electron and the hole bands are cross each other around the Fermi level in case of MgB2C. This dispersion in different high symmetric points enables us to know the effect of carbon on the electronic structure and density of state of hole bands to change the critical temperature of super conductors. Their crystal structure in case of the three compounds is the same to be hexagonal closed packed structures. We also calculated Tc using reasonable approximations, and we found that, Tc=27.07 K, 37.34 K, and 41.09k for MgB2C, MgB2 and MgBC respectively. In MgB, quite large number of bands are crossing the Fermi level.