Insights into the structures and elastic properties of Mg-Sn compounds with superconductivity

The CALYPSO crystal structural search in combination with first-principles calculations are performed to explore the crystalline structures and elastic properties, and superconductivity of Mg-Sn compounds. A novel stoichiometry of Mg4Sn with space group Cmmm has been predicted for the first time, which is different from the previously reported structures of Mg3Sn and Mg2Sn. Compared with P63/mmc-Mg3Sn and Mg2Sn, the Mg4Sn and Pm-3m-Mg3Sn possess excellent ductility. Calculated elastic anisotropy index, 3D shear and Young's modulus imply that these four Mg-Sn compounds are anisotropic. More importantly, Mg4Sn and Pm-3m-Mg3Sn can be the potential superconductors. The superconducting transition temperature of Mg4Sn is predicted to be 2.49K at 0 GPa, which is similar to other binary compound of SnSb (below 1.50K) [Phys. Rev. Mater. 3 (2019) 084603], and slightly lower than 5.03K of Pm-3m-Mg3Sn. In addition, the favorable adsorption site for Mg2Sn(001) and Mg4Sn(001) surfaces is hollow site, whereas for Pm-3m-Mg3Sn(001) and P63/mmc-Mg3Sn(001) surfaces is top sites (T1).