Modeling of punctual defects in UAL{sub 4} from the U-Al system: Combination of CALPHAD method with first principles calculation; Modelado de defectos puntuales en UAl4; combinacion del metodo CALPHAD con calculos de primeros principios

We investigated the point defect structure of oI20 UAl{sub 4} in order to study aluminum diffusion. We performed ab initio calculations within a pseudopotentials method implemented in the Vienna Ab initio Simulation Package (VASP) to obtain point defect formation energies: vacancies (V{sup U} and V{sup A}l ) and antisites (Al{sup U} and U{sup A}l). Using a statistical-thermodynamic model we calculated defects concentrations as function of temperature and deviation from stoichiometry. For stoichiometric UAl{sub 4} antisites are the dominant thermal defects. In off-stoichiometric UAl{sub 4}, antisites are the constitutional defects. For U-rich UAl{sub 4}, the thermal defect is called Entre Ramas, where one antisite U atom is replaced by five Al vacancies. For Al-rich UAl{sub 4}, the thermal defect is also an Entre Ramas, where four antisite Al atoms are replaced by five U vacancies. Our first principles results were used to model UAl{sub 4} intermediate phase with a two sublattices Wagner-Schottky model. The Thermocalc data bases previously used were modified, including antisites and vacancies in both sublattices of the UAl{sub 4} intermediate phase: (U,Al,VA){sub 0.2}: (Al,U,VA){sub 0.8}. We obtained a consistent thermodynamic database able to reproduce the entire U-Al equilibrium phase diagram (author)