The new solid solution of double transition metal MXenes: Atomistic modeling of two-dimensional YScX (X= C and N)

Abstract

In this paper, the structural and dynamical stability, electronic, optical, and thermodynamic properties of a new solid solution of two transition metals YScX (X = C and N) MXenes have been studied. The calculation is carried out based on density functional theory (DFT) and the pseudopotential technique. The results obtained from the structural, thermodynamical, and dynamical stability have shown that 2D YScC and YScN MXenes are structurally stable and their experimental synthesis is possible. Total density of states and band structure calculations show that YScX (X = C and N) MXene exhibits metallic behavior using LDA, GGA, and GGA + HSE06 approximations. According to the total density of states results, it can be concluded that the YScX MXenes have a pseudogap close to the Fermi level and at the left side, which justifies the structural stability of the studied monolayers. The plots of electron charge density distribution and electron localization function justify the metallic nature of the mentioned structures. The large negative values of the real part of the dielectric function indicate that 2D YScX (X = C and N) MXenes have a metallic Drude-like behavior. The saturation of the surface of 2D monolayers with various F, O, OH, and H functional groups does not change the metallic properties, the only exception that reveals the semiconductor property in the HSE06 method is YScCH2 Mxene where no atomic orbital intersects the Fermi level. In addition, the onset of the absorption spectrum of YScX (X = C and N) MXenes corresponds to zero photon energy, which is a confirmation of the metallic properties of the investigated structures. The GGA + HSE06 method enables faster electromagnetic beam propagation through the 2D materials, particularly in the x-direction of the hexagonal structure, resulting in a lower absorption coefficient and optical conductivity of 2D monolayers compared to the GGA method. The rising trend of entropy with temperature provides evidence for the endothermic behavior of YScC and YScN monolayers. Unlike heat capacity, the Debye temperature of YScX (X = C and N) MXenes decreases with respect to temperature T, according to the inverse relationship between the Debye temperature and the heat capacity. Due to structural and dynamic stability and layered structure with the nature of covalent and metallic bonds, YScX MXenes are a suitable choice for use in electrical connections and as a protective coating with a low friction level.