Dioxides transition metal monolayers: A first-principles calculations

We carried out first-principles computational calculations within the framework of density functional theory using the generalized gradient approximation along with the pseudo-potential method, in order to investigate the structural and electronic properties and the energy stability of ternary bidimensional alloys based on TMxV1-xO2 (TM = Cr, Mo, and W) for x = 0.0, 0.25, 0.50, 0.75, and 1.0 transition metal dioxides in the 1H structure (group #187). We found that the values of the lattice constants of the VO2, CrO2, MoO2 and WO2 monolayers are in good agreement with reported results and that the lattice constants of ternary alloys obey Vegard's law, with a maximum deviation of 0.362% (less than 1%) for the alloy W0.25V0.75O2. We found that the values calculated for formation energies are negatives, therefore the ternary monolayers are thermodynamically stable. In addition, we found that the Cr0.25V0.75O2 monolayer has a half-metallic character with a magnetic moment of 1.0 mu B/cell, while the Mo0.25V0.75O2 and W0.25V0.75O2 monolayers exhibit a metallic behavior, with magnetic moments of 0.40 mu B/cell and 1.16 mu B/cell, respectively. These magnetic properties come from the hybridization between the V -d, Cr -d, and O -p orbitals. The TMxV1-xO2 (TM = Cr, Mo, and W, with x = 0.50 and 0.75) alloys exhibit a metallic behavior and do not exhibit magnetic properties. In particular, we carried out a study of the mechanical and dynamic stability of the Cr0.25V0.75O2 monolayer, in view of the fact that it is the system of greatest interest for applications in spintronics, through calculations of the elastic constants (a criterion for mechanical stability) and calculations of the vibrational properties of the lattice (phonons).