First-principles investigation of mechanical properties, elastic anisotropy, and ultralow lattice thermal conductivities of ductile Mg-Bi alloys

The crystal structures, mechanical properties, anisotropic properties, and lattice thermal conductivities of Mg-Bi alloys have been investigated by particle swarm optimization structure prediction method and first-principles calculations. Apart from the well-known stoichiometry of Mg3Bi2, the novel stable stoichiometry of Mg4Bi, as well as several metastable stoichiometries (i.e., Mg3Bi, Mg2Bi, and MgBi) are predicted. Meanwhile, the calcu-lated phonon dispersion curves and elastic constants show that the above five Mg-Bi alloys are dynamically and mechanically stable, respectively. Moreover, the calculated mechanical properties indicate that the studied Mg-Bi alloys with various stoichiometries behave ductility. Simultaneously, they exhibit obvious anisotropic characters and the degree of anisotropy follows the order of MgBi > Mg2Bi > Mg3Bi > Mg4Bi > Mg3Bi2. More importantly, the minimum lattice thermal conductivities of MgBi and Mg2Bi are smaller than that of the well-known Mg3Bi2. The adsorption of O atom on the Mg3Bi (001) surface is more sensitive compared with other four Mg-Bi (001) surfaces.

Automated summary

In this study, the crystal structures, mechanical properties, anisotropic properties, and lattice thermal conductivities of Mg-Bi alloys were investigated using particle swarm optimization structure prediction method and first-principles calculations. The results predicted a novel stable stoichiometry of Mg4Bi in addition to the well-known stoichiometry of Mg3Bi2, as well as several metastable stoichiometries. The Mg-Bi alloys exhibited ductility and obvious anisotropic characters. Furthermore, the minimum lattice thermal conductivities of MgBi and Mg2Bi were found to be smaller than that of Mg3Bi2, and the adsorption of O atom on the Mg3Bi (001) surface was more sensitive than on other surfaces.