Stability of the AlF3 surface in H2O and HF environments: An investigation using hybrid density functional theory and atomistic thermodynamics

Thermodynamic calculations based on hybrid-exchange density functional theory are used to predict the surface structure and stability of α-AlF3 ( 0 1 1 ¯ 2 ) in the presence of gaseous HF and H2O environments. The clean stoichiometric α-AlF3 ( 0 1 1 ¯ 2 ) is predicted to be Lewis acidic. However, under most reaction conditions this surface is unstable with respect to the adsorption of hydroxyl ions. This is consistent with experimental observations. It is predicted that the surface containing no hydroxyl ions could only be realised at high temperatures and under unrealistically dry conditions.