Research On D8_m-Mo₅Si₃ Point Defect Structure And Surface Behavior Based On First Principles

Alloying is an important approach to improve the high temperature oxidation resistance of D8_m-Mo₅Si₃.However,the point defects will inevitably appear in this process,which has a significant influence on the material properties and structure of Mo₅Si₃.Moreover,the oxidation resistance of the Mo₅Si₃ has a close relationship with the surface properties.The study of the surface property can lay a foundation for exploring the adsorption mechanism of oxygen on the surface in the future.Considering the requirement of accuracy and the difficulty of experimental measurement,the theoretical research has become an important method to understand the properties of materials.Therefore,the first-principles calculation is employed to investigate the structure stability of point defects and surfaces for D8_m-Mo₅Si₃in this paper.The main conclusions are as follows:1.The formation energies,point defect concentrations and electronic structures of point defects for D8_m-Mo₅Si₃ compound were calculated by the first-principles pseudopotential plane-wave method.The effect of bonding behaviors and structural stability of point defects for D8_m-Mo₅Si₃ compound was investigated emphatically.The results show that the lattice constants of Mo₅Si₃ are 9.6808?,4.9033?,and bulk modulus is 247.08 GPa.The Mo vacancy-induced charge density shows the spindle-like bonding characteristic,and the localized hybridization focuses on Mo-4d state and Si-3p state.It can be seen from the formation energies that Mo_Si1i1 and Si_Mo2 are the most stable defect structures in Mo-rich and Si-rich alloys,respectively.It is because the larger charge accumulation between Mo and Si atoms strengthens the interaction for Mo_Si1i1 and Si_Mo2 anti-site defects.Combining with Wagner-Schottky model,the point defect concentrations at 2173 K as function of composition are also investigated,and the results show that Mo_Si1i1 and Si_Mo2 are the main defect forms of Mo-rich and Si-rich alloys,respectively.2.Atomic relaxations,surface energies and electronic structures of the（100）,（001）and（110）surfaces for D8_m-Mo₅Si₃ are investigated to analyze the surface stability by DFT（Density Functional Theory）based first-principles plane-wave pseudo-potential calculations.The atomic relaxation and surface energy results reflect minimum relaxations of the（ns-8Mo4Si）-terminated（001）,（ns-4Si）-terminated（110）and（ns-2Si-2）-terminated（100）surfaces.Moreover,the（ns-8Mo4Si）-terminated（001）and（ns-4Si）-terminated（110）surfaces are most stable under Si-poor and Si-rich conditions,respectively.The density of states indicates that the surface electronic structures are mainly influenced by the atomic relaxations.The calculated charge densities show the dependence of the surface relaxation mainly on dangling bonds.According to the calculated surface energies,the predicted crystal shapes show the octagonal prism and a structure which is close to cuboid in them_Ss_ilab-m_Sb_iulkrange from-1.077 eV to-0.546 eV and-0.546 eV to 0 eV,respectively.These calculation results are consist with the previous reports.