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 Mg 4 Sn with space group Cmmm has been predicted for the first time, which is different from the previously reported structures of Mg 3 Sn and Mg 2 Sn. Compared with P 63 /mmc -Mg 3 Sn and Mg 2 Sn, the Mg 4 Sn and Pm- 3 m -Mg 3 Sn possess excellent ductility. Calculated elastic anisotropy index, 3D shear and Young's modulus imply that these four Mg-Sn compounds are anisotropic. More importantly, Mg 4 Sn and Pm- 3 m -Mg 3 Sn can be the potential superconductors. The superconducting transition temperature of Mg 4 Sn 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- 3 m -Mg 3 Sn. In addition, the favorable adsorption site for Mg 2 Sn(001) and Mg 4 Sn(001) surfaces is hollow site, whereas for Pm- 3 m -Mg 3 Sn(001) and P 63 /mmc -Mg 3 Sn(001) surfaces is top sites (T 1). • A novel stoichiometry of Mg 4 Sn with space group Cmmm has been first predicted. • The Mg 4 Sn and Pm- 3 m -Mg 3 Sn possess excellent ductility. • The Tc of Mg 4 Sn is predicted to be 2.49K at 0 GPa and slightly lower than 5.03K of Pm- 3 m -Mg 3 Sn. [ABSTRACT FROM AUTHOR]