First-principles investigation of the structural and dynamical stability, electronic and thermal properties of two-dimensional Yn+1Cn (n=1, 2, and 3) MXenes

This paper studies the structural and dynamical stability, electronic and thermal properties of two-dimensional Yn+1Cn (n = 1, 2, and 3) MXenes in the hexagonal structure. The calculations are carried out using the computational software package QUANTUM-ESPRESSO/PWSCF based on density functional theory (DFT) and the pseudopotential method. The calculated lattice parameters a and c are in good agreement with the previous theoretical and experimental studies. Structural calculations described that Y4C3 is more stable than Y3C2 and Y2C. Analyzing cohesive energy indicates that the structural stability of these compounds increases with increasing n-index due to the increase in the number of stronger bonds between Y and C atoms in the thicker MXene monolayers. The phonon dispersion calculations show that the Yn+1Cn MXenes are dynamically stable at ambient pressure, and it is possible to be experimentally synthesized. Based on the electronic results, it can be argued that the Yn+1Cn has a metallic behavior in the hexagonal structure. Also, the electron charge density distribution confirms the metallic behavior of Yn+1Cn structures. The thermodynamic calculations indicate that enthalpy increases continuously and steadily by increasing pressure and n-index in the Yn+1Cn structures. Generally, for Yn+1Cn (n = 1, 2, and 3) MXenes with the increasing n-index, Debye temperature and stiffness decrease, followed by heat capacity increases.