First-principle investigation of native and impurity defects in

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

Corresponding author: fabio.bernardini@dsf.unica.it

Received: 6 July 2006
Accepted: 18 September 2006

Abstract

We use first-principles techniques to investigate the properties of native defects and impurities in . We focus our investigation on those defects that could have a relevant role in and co-doped . 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 and 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.