Binding Energies in the Molten M–Al–Zr–O–F Systems (M = Li, Na, K)

Abstract

The binding energies in complex anions formed from the components Al–F, Zr–F, Al–O–F, and Zr–O–F are calculated by the ab initio Siesta molecular dynamics simulation. The formation of the anions is related to the dissolution of the ZrO₂ and Al₂O₃ oxides in MF–AlF₃ (M = Li, Na, K) fluoride melts. The influence of the element compositions of the anions and the cation from the second coordination sphere on the binding energies of the complex anions is determined. Among the oxygen-containing anions, the \({\text{A}}{{{\text{l}}}_{{\text{2}}}}{{{\text{O}}}_{{\text{2}}}}{\text{F}}_{{\text{6}}}^{{2 - }}\) and \({\text{Z}}{{{\text{r}}}_{{\text{2}}}}{{{\text{O}}}_{{\text{2}}}}{\text{F}}_{{\text{6}}}^{{2 - }}\) anions are shown to be most stable. Under identical conditions, the anions formed by zirconium are characterized by the lowest energy of the determining bond. The replacement of the cation in the second coordination sphere in the series from K to Li decreases the binding energy in the M₂Al₂O₂F₆ and M₂Zr₂O₂F₆ anions.