Atomistic Origin of Phase Stability in Oxygen-Functionalized MXene: A Comparative Study

Oxygen-functionalized MXene, M2CO2 (M = group III–V metals), are emergent formidable two-dimensional (2D) materials with a tantalizing possibility for device applications. Using first-principles calculations, we perform an intensive study on the stability of fully O-functionalized (M2CO2) MXenes. Depending on the position of O atoms, the M2CO2 can exist in two different structural phases. On one side of MXene, the O atom occupies a site which is exactly on the top of the metal atom from the opposite side. On the other side, the O atom can occupy either the site on the top of the metal atom of the opposite side (BB′ phase) or on the top of the C atom (CB phase). We find that for M = Sc and Y the CB phase is stable, whereas for M = Ti, Zr, Hf, V, Nb, and Ta the stable phase is BB′. The electron localization function, the atom-projected density of states, the charge transfer, and the Bader charge analyses provide a rational explanation for the relative stability of these two phases and justify the ground sta...