Capture of Lanthanum Atoms by the (111) Twin Boundary in Fluorite: A DFT Study

Ab initio calculations were performed to estimate the energy preference of Ca2+ substitution by La3+ with compensating incorporation of an additional F- ion at the (111) twin boundary of fluorite (CaF2). Model structures of polytypes and polysomes, which are periodic stacking faults within the cubic fluorite matrix, were constructed and optimized using density functional theory (DFT). Our results indicate that the twin boundary has a strong tendency to trap lanthanum cations. These findings suggest that the twin boundaries in CaF2 may act as active sites for the accumulation of rare-earth elements, providing potential routes for modifying the functional properties of the materials. Conversely, addition of lanthanoids may promote growth twinning of fluorite.