Potential Interaction of Noble Gas Atoms and Anionic Electrons in Ca2N

Noble gas (NG) is often used as a hydrostatic pressure-transmitting medium in high-pressure experiments. However, the NG atoms under compression are found to be readily trapped in the voids of some ionic compounds. Electrides usually have large open frameworks and show strong hydrogen and oxygen affinities. To investigate the interaction of light NG with electrides under pressure, we perform the structural investigations of Ca2N in a diamond anvil cell under different NG (He, Ne, and Ar) conditions, assisted by density functional theory calculations. Experimental results find that in comparison with nonhydrostatic pressure, transition paths of Ca2N change with different pressure media and phase transition pressure is reduced significantly, and NG is chemically inert for electrides in the studied pressure range. Theoretical analysis indicates that the anionic electrons in Ca2N electride show strong repulsion with NG, preventing NG atoms from entering electrides. Such repulsion is due to the almost neutral character of noble atoms in electrides, which makes it difficult for them to interact with anionic electrons. Moreover, in the predicted metastable Ca2N-NG, the neutral features of NG atoms result in the reservation of the intrinsic electride character. Our results reveal that the NGs can be used as protective gases for electrides under ambient conditions or hydrostatic pressure-transmitting media for the studies of high-pressure electrides within 50 GPa.