Europhys. Lett.
Volume 76, Number 3, November 2006
Page(s) 491 - 497
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 11 October 2006
Europhys. Lett., 76 (3), pp. 491-497 (2006)
DOI: 10.1209/epl/i2006-10297-y

First-principle investigation of native and impurity defects in $\chem{MgB_{2}}$

F. Bernardini and S. Massidda

SLACS-CNR and Dipartimento di Fisica, Università di Cagliari Cittadella Universitaria, I-09124 Monserrato (CA), Italy

received 6 July 2006; accepted in final form 18 September 2006
published online 11 October 2006

We use first-principles techniques to investigate the properties of native defects and impurities in $\chem{MgB_{2}}$. We focus our investigation on those defects that could have a relevant role in $\chem{Al}$ and $\chem{Li}$ co-doped $\chem{MgB_{2}}$. This system shows an anomalous dependence of superconductivity on doping concentration, not yet understood. Structural effects such as segregation and clustering have been put forward to justify experimental evidence. Here we show that native defects have very high formation energies, that $\chem{Al}$ and $\chem{Li}$ do not form aggregates and incorporate as substitutional defects randomly distributed on the Mg sublattice sites. There exists a competition between segregation and incorporation of Li, the latter being slightly favored energetically. Our results suggest that anomaly in the superconducting behavior must be accounted for by electronic structure effects.

74.62.Dh - Effects of crystal defects, doping and substitution.
61.72.Bb - Theories and models of crystal defects.
74.70.Ad - Metals; alloys and binary compounds (including A15, $\chem{MgB_{2}}$, etc.).

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