First principles investigation of the crystal and electronic structures of CeNCl and “CeNF”

•Complementing experimental determination of tetragonal CeNCl and providing electronic band structure.•Proposing CeNF in rhombohedral structure ground state versus tetragonal from energy criteria.•Similarly to isoelectronic CeO2, both CeNF and CeNCl are insulating with smaller band gaps.•Proposing synthesis routes for CeNF based on ammonolysis and fluorination.

Based on DFT energy discrimination and detailed electronic and bonding properties, it is shown that the hitherto unexplored cerium nitride fluoride can be obtained in rhombohedral ThNF structure whereas actual CeNCl is confirmed in the early determination with PbFCl-like structure. The respectively adopted 3D and 2D like structures are assigned to the major role played by the F polarizability, four times smaller than Cl. In their ground state both compounds are found small gap insulators with 1.9 eV (CeNCl), 1.8 eV (CeNF) compared to insulating isoelectronic cerine CeO2 with 2.2 eV band gap. The bonding shows balance between covalence brought by Ce–N bond versus ionic Ce–F(Cl) bonding and d(Ce–N) < d(Ce–F(Cl)) distances. Synthesis routes for CeNF are proposed.

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