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

Abstract

The mechanisms of ionic conductivity in BaLiF₃ 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 BaLiF₃ 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 Ba²⁺ ↔ 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 BaLiF₃.