Investigation on the effects of native defects on electronic structure in MgB2 by first-principles calculation

The decrease of Currie temperature in milled MgB2 could be caused by some native point defects such as vacancies, antisites, and interstitials. In order to clarify it, the formation energies of the native point defects in MgB2 were examined, and the influence of the stable defects on its electronic structure was investigated by first-principles calculation. It was found that the B interstitials and the B vacancies have the lowest formation energies under Mg-rich (Mg:B > 1:2) and Mg-poor (Mg:B > 1:2) conditions, respectively, compared to other native point defects. The density of states at the Fermi level for MgB2 with and without point defects is mainly comprised of the B’s p orbital. Under Mg-poor conditions, the partial density of states (at the Fermi level) of the B’s p orbital for MgB2 with B interstitials reduces with the increase of its concentration. Under Mg-rich conditions, the B vacancies first increase and then decrease the partial density of states at the Fermi level of the B’s p orbital as its content increases.