Fig. 6
From: Reactivity of He with ionic compounds under high pressure

The changes of the volume as a function of pressure for He insertion. a MgF2, b MgO, c LiF, d Li2O, e CaF2, and f Na. The dashed lines refer to a sum of the volume of the ionic compounds and elemental helium, whereas the solid line is for the ternary compound. Shaded areas present the pressure intervals of stable He insertion