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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]

The dynamical, mechanical, anisotropic, and thermodynamic properties of Mg-XL-Y (XL = Zn, Al) alloys based on three long-period stacking ordered (LPSO) phases (ie, 10H, 14H, and 18R) have been investigated systematically by first-principles calculations. The LPSO phases of Mg-XL-Y (XL = Zn, Al) alloys are thermodynamically, dynamically, and mechanically stable. The each LPSO phase of Mg–Al–Y alloys has superior mechanical properties with larger resistances to deformation under applied stress and shear pressure, stiffness, as well as hardness than those of corresponding to LPSO phases of Mg–Zn–Y alloys. According to universal elastic anisotropic index, percent shear anisotropy, 3D surface structures of Young's moulus, and sound velocities, the LPSO phases of Mg-XL-Y (XL = Zn, Al) alloys exhibit obvious anisotropy. Besides, all LPSO phases of Mg-XL-Y (XL = Zn, Al) alloys possess low lattice thermal conductivity due to the strong anharmonicity. The calculated adsorption energies indicate that the 14H(001) surface of Mg–Al–Y system at the hollow site is more sensitive to absorb O atom. • Three long-period stacking ordered (LPSO) phases (ie, 10H, 14H, and 18R) are thermodynamically, dynamically, and mechanically stable. • Each LPSO phase of Mg–Al–Y alloys has superior mechanical properties with larger resistances to deformation under applied stress and shear pressure, stiffness, as well as hardness than those of corresponding to LPSO phases of Mg–Zn–Y alloys. • LPSO phases of Mg-XL-Y (XL = Zn, Al) alloys exhibit obvious anisotropy and low lattice thermal conductivity. [ABSTRACT FROM AUTHOR]

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 Mg 3 Bi 2 , the novel stable stoichiometry of Mg 4 Bi, as well as several metastable stoichiometries (i.e., Mg 3 Bi, Mg 2 Bi, and MgBi) are predicted. Meanwhile, the calculated 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 > Mg 2 Bi > Mg 3 Bi > Mg 4 Bi > Mg 3 Bi 2. More importantly, the minimum lattice thermal conductivities of MgBi and Mg 2 Bi are smaller than that of the well-known Mg 3 Bi 2. The adsorption of O atom on the Mg 3 Bi (001) surface is more sensitive compared with other four Mg–Bi (001) surfaces. • Apart from the well-known stoichiometry of Mg 3 Bi 2 , the novel stable stoichiometry of Mg 4 Bi, as well as several metastable stoichiometries (i.e., Mg 3 Bi, Mg 2 Bi, and MgBi) are predicted. • The five Mg–Bi alloys are dynamically and mechanically stable. • The five Mg–Bi alloys behave ductility and obvious anisotropy. • The minimum lattice thermal conductivities of MgBi and Mg 2 Bi are smaller than that of Mg 3 Bi 2. [ABSTRACT FROM AUTHOR]

(Ti,Nb) 3 SiC 2 /60 vol%-Al 2 O 3 composite ceramic samples with different Ti/Nb atomic ratios were prepared by hot-pressing sintering using Ti/Si/Al/TiC/NbC/Al 2 O 3 powders as starting materials. X-ray diffraction analysis showed that the solid solubility of Nb is approximately 7.5 at%. Excessive NbC powder addition can lead to the generation of an impurity phase. Scanning transmission electron microscopy and X-ray photoelectron spectroscopy images reveal that most of the Nb-doped atoms aggregate at 2a -sites, as this configuration exhibits the lowest system energy. The optimized hardness, flexural strength and fracture toughness of (Ti,Nb) 3 SiC 2 /Al 2 O 3 were determined to be 16.0 GPa, 672 MPa and 6.9 MPa m1/2, which corresponds to an increase of 15.9%, 18.7% and 25.4% respectively, compared with Ti 3 SiC 2 /Al 2 O 3 composite ceramics. By means of first-principle calculations, the strengthening mechanism is derived from both intragranular improvement in (Ti,Nb) 3 SiC 2 solid solutions and intergranular enhancement of (Ti,Nb) 3 SiC 2 /Al 2 O 3 grains interfaces. [ABSTRACT FROM AUTHOR]