On the mechanisms of ionic conductivity in BaLiF3: a molecular dynamics study

The mechanisms of ionic conductivity in BaLiF(3) are investigated using molecular simulations. Direct molecular dynamics simulations of (quasi) single crystalline super cell models hint at the preferred mobility mechanism which is based on fluoride interstitial (and to a smaller extent F(-) vacancy) migration. Analogous to previous modeling studies, the energy related to Frenkel defect formation in the ideal BaLiF(3) crystal was found as 4-5 eV which is in serious controversy to the experimentally observed activation barrier to ionic conductivity of only 1 eV. However, this controversy could be resolved by incorporating Ba(2+)↔ Li(+) exchange defects into the elsewise single crystalline model systems. Indeed, in the neighborhood of such cation exchange defects the F(-) Frenkel defect formation energy was identified to reduce to 1.3 eV whilst the cation exchange defect itself is related to a formation energy of 1.0 eV. Thus, our simulations hint at the importance of multiple defect scenarios for the ionic conductivity in BaLiF(3).