First principles study of 3d transition metal doped Cu3N

Interstitially doped Cu3N represents a model system to study “enclosed atoms” in a cuboctahedral environment. Based on density functional theory calculations using the generalized gradient approximation, we report a systematic study of 3d-transition metals (TM), as well as Li-, H-, and Pd-doped Cu3N, whose stabilities and magnetic properties are investigated. The interposition of 3d-TM atoms leads to mechanically stable yet brittle structures, with Sc, Mn, Ni, Cu, Zn possessing relatively small positive (endothermic) formation energies (0.12∼0.54eV/TM), suggesting it may be easier to realize them experimentally than other 3d-TM elements. Li-, H-, Pd-doping in Cu3N are exothermic, while Ti, V, Cr, Fe, and Co have higher formation energy (0.93∼1.39 eV/TM) at a doping concentration 3.7 %. The fully 3d-TM doped Cu3N systems exhibit a wide spectrum of magnetic properties, ranging from weak antiferromagnetic (Sc-), antiferromagnetic (Ti-, V-, Cr-) to ferromagnetic (Mn-, Fe-, Co-) and non-magnetic (Ni-, Cu-, Zn-) behaviour. In particular, Ti:Cu3N exhibits weak itinerant magnetic properties with a large positive magnetovolume effect. All the 3d-TM atom intercalations into cubic Cu3N lead to a semiconductor-to-metal transition for both 100% and 3.7% doping, with the exception of Ni:Cu3N exhibiting a weak metallic or narrow semiconducting behaviour depending on the doping concentration.