Chemical interactions between helium and VF3-type compounds.*

Helium is the second most abundant element in the universe and coincidentally, the least reactive. It is a relatively scarce element in Earth's atmosphere, nevertheless, non-negligible quantities of this element may still be trapped in the interior parts of our and other rocky planets. On the other hand, helium can be found in larger amounts in giant plants like Jupiter and Saturn. As consequence, the chemistry of helium under extreme condition is of great importance in planetary science. Computational methods and experiments have revealed that this element that is traditionally thought of as being inert, in combination with other compounds, like pure metals or ionic salts, can form a variety of interstitial, stable, systems.

In our work, we have studied the reactivity and interactions between helium and VF-type compounds, such as AlF3, a perovskite like structure having a vacant A-site, with first principles calculations. We observed that not only He can form stable compounds occupying the vacancy in the VF-type compounds, increasing notably properties like the bulk modulus, but it is also activated by the chemical environment. The possibility for chemical bond formation with He is discussed.