Atomistic Origin of Phase Stability in Oxygen-Functionalized MXene*

Oxygen-functionalized MXene, M₂CO₂ (M =group III−V metals), are two-dimensional (2D) materials with the immense possibility for device applications. Using first-principles calculations, we perform a study on the stability of M₂CO₂ MXenes. Depending on the position of O atoms, the M₂CO₂ can exist in two different phases. CB phase, where O at the top of carbon and metal atom. On the other side, O atom can occupy either the site on the top of the metal atom (BB′ phase). We found 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 and atom-projected density of states, provide a rational explanation for the relative stability. Instability of BB′- M₂CO₂ (M = Sc and Y) originates from the weakening of M−C interactions due to the motion of C atom in the−b plane. The insight into the stability of these competing structural phases of M₂CO₂ is an important step in the direction of identifying the stable phases of these 2D materials and their applications.

Mishra, A.; Srivastava, P.; Carreras, A.; Tanaka, I.; Mizuseki, H.; Kwang-Ryeol, L.; Singh, A. K. Atomistic Origin of Phase Stability in Oxygen-Functionalized MXene: A Comparative Study. J. Phys. Chem. C, 121, 18947 (2017)