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

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 N-2, N-4, N-5, N-6, and N-8 units. In addition, we identified an infinite helical N-4 chain in I4(1)/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 N-4 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 R3 phase, which has a lower energy than the previously identified P1 phase. For the pentazolate salts, the I4/m CeN10 exhibits ferromagnetism, while the C2 and P2(1)2(1)2 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.