Calcium fluoride (CaF2) is one of the common fluorine compounds, which is mineralogically known as fluorite. It is widely used in the production of 3-dimensionally integrated circuits, optical glass, hydrofluoric acid and ceramics, and as a flux in metallurgic industry. Owing to the increased demand for high-quality fluorite and the decrease in available resources, much attention has been paid to the study on fluorite.
There have been several studies on the characteristics of fluorite surfaces with various Miller indexes by first principles calculations. Fluorite is known as an ionic compound and it is generally cleaved along {111}, {110}, {100} and {310} planes. The cleavage along {111} plane is the easiest, followed by {110} plane and then {310} plane.
Previous studies mainly focused on the characteristics of possible surfaces with different Miller indexes and concluded that fluorite {111} surface is the safest and this is the main cleavage plane. Fluorite is an ionic crystal and calcium and fluorine layers are likely to be stacked alternatively along [111] direction. So, there may be several terminations with the same Miller index {111} surface. However, there have been few reports on the detailed characteristics of fluorite {111} surface.
Ri Chol Jin, a section head at the Faculty of Earth Science and Technology, constructed 3 kinds of possible terminations for fluorite {111} surface and calculated their surface energies, broken bond densities and relaxation degrees by using DFT calculation to determine the safest termination.
This investigation on various terminations offers a new understanding of the characteristics of fluorite {111} surface and provides useful information for further study of surface reactivity and dissolubility of fluorite.
For more information, please refer to his paper “Characteristics of Fluorite {111} Surface with Various Terminations: A DFT Investigation” in “Iranian Journal of Science” (SCI).