Reaction between nickel or iron and xenon under high pressure

Xe-Ni and Xe-Fe systems are studied in a pressure range relevant to the Earth's core (135-210 GPa) using laser-heated diamond anvil cells and synchrotron X-ray diffraction. The stability of several intermetallic compounds, including XeNi3 and XeFe3, has been recently calculated using structural searches and density functional theory (DFT) above 155 and 190 GPa, respectively [Zhu L, Liu H, Pickard CJ, et al. Nat Chem. 2014; 6: 644-648]. We have synthesized XeNi3 around 150 GPa, confirming the prediction; however, it has a cubic Pm (3) over barm-Cu3Au structure, different from the predicted one for XeNi3 but identical to the structure predicted for XeFe3. Pm (3) over barm-XeNi3 is calculated to be metastable with DFT. A disordered Ni1-xXex (x similar to 0.08) alloy is observed to form prior to this compound. This alloy is interesting in the perspective of a possible storage of xenon in the Earth's core. We have not observed any reaction between Xe and Fe up to 210 GPa.