Electronic Structures and Magnetisum in Nitride MXenes

MXenes are graphene-like structured layered inorganic compounds with a stoichiometric formula of M_n+1X_n, where M is an early transition metal such as titanium (Ti), vanadium (V), chromium (Cr), Manganese (Mn), etc., and X being carbon (C), nitrogen (N), or CN. Early transition metals (ETM) have partially filled d-orbitals, which makes them more reactive than late transition metals (LTM) counterparts and exhibit higher oxidation states than LTMs such as Ti can have as high as +4 and Mn can be in as high as +7 oxidation states. Having a lone pair and three unpaired electrons in the valence shell, nitrogen bonds differently with different transition metals. The 3d-orbitals of ETMs hybridize and bond differently with 2p-states of N. In this work, we analyze crystallography, electronic structures, and magnetism of nitride MXenes and the trend in electronic and magnetic properties variation. We theoretically study a series of nitride MXenes using the Vienna ab initio simulation package (VASP) in the framework of the first-principles density functional theory calculations. The calculations show that not all nitride MXenes with ETMs of the 4th period are magnetic, but the magnetism change follows a trend. Interestingly, one of the MXenes in the series Ti₃N₂ has several non-nuclear interstitial anionic electrons (IAEs) trapped within the positively charged lattice framework, making them candidates for an under-explored class of electride materials¹.

This study was funded by the Department of Energy BES-RENEW award number DE-SC0024611.

Reference: ¹Adhikari, C.M.; Thapa, D. et al. "Confinement of quasi-atomic structures in Ti₂N and Ti₃N₂ MXene Electrides" (2024), arXiv:2408.00897.