Elastic constants, electronic structures and thermal conductivity of monolayer XO2 (X = Ni, Pd, Pt)

Abstract

Based on the first-principles calculations, the stability, elastic constants, electronic structure, and lattice thermal conductivity of monolayer <i>X</i>O₂ (<i>X</i> = Ni, Pd, Pt) are investigated in this work. The results show that <i>X</i>O₂ (<i>X</i> = Ni, Pd, Pt) have mechanical and dynamic stability at the same time. In addition, the Young’s modulus of monolayer NiO₂, PdO₂ and PtO₂ are 124.69 N·m^–1, 103.31 N·m^–1 and 116.51 N·m^–1, Poisson’s ratio of monolayer NiO₂, PdO₂ and PtO₂ are 0.25, 0.24 and 0.27, respectively, and each of them possesses high isotropy. The band structures show that monolayer <i>X</i>O₂ (<i>X</i> = Ni, Pd, Pt) are indirect band-gap semiconductors with energy gap of 2.95 eV, 3.00 eV and 3.34 eV, respectively, and the energy levels near the valence band maximum and conduction band minimum are mainly composed of Ni-3d/Pd-4d/Pt-5d and O-2p orbital electrons. Based on deformation potential theory, the carrier mobility of each monolayer is calculated, and the results show that the effective mass and deformation potential of monolayer <i>X</i>O₂(<i>X</i> = Ni, Pd, Pt) along the armchair and zigzag directions show obvious anisotropy, and the highest electron and hole mobility are 13707.96 and 53.25 cm²·V^–1·s^–1, 1288.12 and 19.18 cm²·V^–1·s^–1, and 404.71 and 270.60 cm²·V^–1·s^–1 for NiO₂, PdO₂ and PtO₂, respectively. Furthermore, the lattice thermal conductivity of monolayer <i>X</i>O₂(<i>X</i> = Ni, Pd, Pt) at 300 K are 53.55 W·m^–1·K^–1, 19.06 W·m^–1·K^–1 and 17.43 W·m^–1·K^–1, respectively. These properties indicate that monolayer <i>X</i>O₂ (<i>X</i> = Ni, Pd, Pt) have potential applications in nanometer electronic materials and thermal conductivity devices.