Single-bonded nitrogen chain and porous nitrogen layer via Ce–N compounds

Abstract

Cerium ions can exist in the trivalent or tetravalent forms such as in Ce₂O₃ and CeO₂, respectively. Therefore, they can provide different chemical environments for stabilizing novel polymeric nitrogen species. This article explored the phase diagram of binary Ce–N compounds under pressures of up to 150 GPa using the crystal structure prediction method MAGUS. In this work, we find that nitrogen atoms can exist in the form of N₂, N₄, N₅, N₆, and N₈ units. In addition, we identified an infinite helical N₄ chain in I4₁/a CeN₄ at about 100 GPa. Differing from the well-known zigzag or armchair nitrogen chains which are mixed with single and double bonds, the helical N₄ chain is purely single-bonded. Moreover, it can be quenched to ambient pressure and exhibit excellent denotation properties. We also identified a layered porous nitrogen network in CeN₈. After the removal of cerium atoms, the nitrogen network is also dynamically stable in the R phase, which has a lower energy than the previously identified P phase. For the pentazolate salts, the I4/m CeN₁₀ exhibits ferromagnetism, while the C2 and P2₁2₁2 CeN₁₅ exhibit anti-ferromagnetism. Overall, the newly discovered Ce–N compounds with polymeric nitrogen exhibit fascinating structural and electronic characteristics, which may lead to potential application in areas such as explosives or catalysis.