Ab-initio calculation of formation and migration energies of intrinsic defects in BaF2

We have performed ab-initio calculations of the formation and migration energies of intrinsic defects (interstitials, vacancies and Frenkel defects) in barium fluoride. The calculations were performed within density-functional theory and the generalized-gradient approximation, employing pseudopotentials and a plane-wave basis set. The results agree reasonably well with available experimental data. They are also compatible with calculations and experimental data on calcium fluoride. We found that Frenkel pairs are composed of pairs of charged defects and that their formation energies are 3.44 eV and 1.88 eV for cation and anion, respectively. The lowest barrier for defect migration was found to correspond to the migration of the anion vacancy along the 〈 100 〉 direction (energy barrier of 0.53 eV), which compares well with the experimental value of 0.59 eV. Cation vacancy migration was instead found to require an energy of at least 2.22 eV along the easiest migration path, 〈 100 〉 .