Double transition metal MXenes with wide band gaps and novel magnetic properties

Abstract

Novel wide band gaps and magnetism in ordered titanium–vanadium, titanium–chromium, and titanium–manganese carbide and nitride based MXenes are predicted using density functional theory. Based on the recent synthesis of Ti centred double transition metal MXenes, we study MXenes with a central Ti layer and different surface early 3d metals, and various terminations, TiM₂X₂T (M = V, Cr, Mn; X = C, N; T = H, F, O, OH). While previously studied MXenes are strongly metallic, we predict surface metal and termination dependent metal–insulator transitions in the Cr–N and Mn–N series. A uniquely wide band gap over 1 eV is predicted for TiMn₂N₂F₂ using the HSE06 density functional while the unterminated TiMn₂N₂ remains metallic. The entire TiCr₂C₂T series is predicted to be semiconducting. Distinct from the more common Ti–C MXenes, not all combinations of metals and terminations are predicted to be stable. Within the examined sets of materials, anti-ferromagnetic orders are generally most favorable. The new MXenes further extend the range of properties accessible in this family of two-dimensional nanomaterials.