En las fronteras de la Materia Condensada

We present an ab initio study of the electronic structure and the structural relaxations introduced by Cd and Ta impurities when they replace cations in a series of binary oxides. Calculations were performed with the FLAPW method that allows us to treat the electronic structure and the atomic relaxations in a fully self-consistent way. We considered different charge states for each impurity and obtained that electronic properties, in particular the Electric Field Gradient (EFG), are strongly dependent on these charge states. As ¹¹¹Cd and ¹⁸¹Ta are TDPAC probes we can compare the theoretical predictions with available experimental determinations of the EFG tensor or design key experiments to check specific theoretical predictions as we did in the case of TiO₂ where we confirm that Cd is in a charge state and that the EFG tensor changes the orientation of its principal component with respect to the pure system ^[1]. We study compounds with a variable degree of ionicity: TiO₂, SnO₂ and In₂O₃ and obtained that the simple models (like Point Charge with antishielding factors) can not describe the measured EFG tensor even in systems with a high degree of ionicity.

[1] L.Errico et al. Phys. Rev. Lett. 89, 055503 (2002).

This research was partially supported by Fundación Antorchas, ANPCyT (PICT 03-03727), and CONICET, Argentina, and TWAS, Italy.