Effects of Doped Elements (Si, Cr, W and Nb) on the Stability, Mechanical Properties and Electronic Structures of MoAlB Phase by the First-Principles Calculation

Abstract

First-principles calculations based on density functional theory (DFT) have been performed to explore the effects of Si, Cr, W, and Nb elements on the stability, mechanical properties, and electronic structures of MoAlB ternary boride. The five crystals, with the formulas of Mo4Al4B4, Mo4Al3SiB4, Mo3CrAl4B4, Mo3WAl4B4, and Mo3NbAl4B4, have been respectively established. All the calculated crystals are thermodynamically stable, according to the negative cohesive energy and formation enthalpy. By the calculation of elastic constants, the mechanical moduli and ductility evolutions of MoAlB with elemental doping can be further estimated, with the aid of B/G and Poisson’s ratios. Si and W doping cannot only enhance the Young’s modulus of MoAlB, but also improve the ductility to some degree. Simultaneously, the elastic moduli of MoAlB are supposed to become more isotropic after Si and W addition. However, Cr and Nb doping plays a negative role in ameliorating the mechanical properties. Through the analysis of electronic structures and chemical bonding, the evolutions of chemical bondings can be disclosed with the addition of dopant. The enhancement of B-B, Al/Si-B, and Al/Si-Mo bondings takes place after Si substitution, and W addition apparently intensifies the bonding with B and Al. In this case, the strengthening of chemical bonding after Si and W doping exactly accounts for the improvement of mechanical properties of MoAlB. Additionally, Si doping can also improve the Debye temperature and melting point of the MoAlB crystal. Overall, Si element is predicted to be the optimized dopant to ameliorate the mechanical properties of MoAlB.

CO2 capture and storage by metal and non-metal decorated silicon carbide nanotubes: a DFT study

“…After doping, it was observed that the SiC nanotube was not stable when these dopants were used to replace C atoms; however, the nanotubes became very stable when the Si atom was replaced by Al, B or N dopants. Additionally, Si atoms were displaced towards the tube axis while C atoms were displaced in the opposite direction consistent with previous reports [16]. Figure 1 presents the optimized structures of the CO 2 -adsorbed SWSiCNT systems with different dopants.…”

Helium-induced damage in MAB phase MoAlB and Fe2AlB2: first-principles simulation

“…In recent years, the influence of different synthetic method [26][27][28][29], coating deposition condition [30,31] and application environment [32][33][34][35] on these properties have also been taken into consideration. Doping and solid-solution have been introduced to further improve the mechanical, electrical, thermal and oxidation resistant properties of these two materials [36][37][38][39][40]. MoAlB and Fe 2 AlB 2 have also served as precursors for two-dimensional MBene with excellent electrical, magnetic and electrocatalytic performance [41][42][43] and reinforcement component in composite materials to increase the wear and oxidation resistance [44][45][46][47].…”