Atomic mechanisms of superionic conductivity in fluorite

The subsequent melting/crystallization of the two sub-lattices of CaF₂ is explored by molecular dynamics simulations. Both, heating from 100 K and cooling from 2500 K encompasses two transitions, i.e. the melting/recrystallization of the fluoride sub-lattice and the of whole crystal at different temperatures. Solid state F^? ion conductivity is observed in a temperature range of about 1500–2000 K which reflects a reasonable agreement with the experiment. A systematic study of fluoride migration revealed the atomistic mechanisms of the spontaneous formation of Frenkel defects, followed by void translocation and terminated by recombination of interstitial fluoride ions and vacancies.