5 Stability of xenon oxides at high pressures

Materials under extreme pressure usually exhibit exotic physical and chemical behaviors. Here, we focus on the variation of stoichiometry under pressure. Xe-O system is studied in this chapter. Anther similar work on Mg-O system is reported in chapter 6.

Xenon, quite inert at ambient conditions, may become reactive under pressure. The possibility of formation of stable xenon oxides and silicates in the Earth’s interior could explain the missing xenon paradox. Using the ab initio evolutionary algorithm, we predict the thermodynamical stabilization of Xe-O compounds at high pressures (XeO, XeO$_2$ and XeO$_3$ at pressures above 83, 102 and 114 GPa, respectively). Our calculations indicate large charge transfer in these oxides, suggesting that large electronegativity difference and pressure are the key factors favoring the formation of xenon compounds. Xenon compounds in the Earth’s mantle, however, cannot directly explain the missing xenon paradox: xenon oxides are unstable in equilibrium with metallic iron in the Earth’s lower mantle, while xenon silicates are predicted to spontaneously decompose at all mantle pressures ($<$136 GPa). This does not preclude Xe atoms from being retained in defects of mantle silicates and oxides.