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  • Theoretical prediction, syn...
    Xu, Qiang; Zhou, Yanchun; Zhang, Haiming; Jiang, Anna; Tao, Quanzheng; Lu, Jun; Rosén, Johanna; Niu, Yunhui; Grasso, Salvatore; Hu, Chunfeng

    Journal of advanced ceramics, 08/2020, Letnik: 9, Številka: 4
    Journal Article

    Guided by the theoretical prediction, a new MAX phase V 2 SnC was synthesized experimentally for the first time by reaction of V, Sn, and C mixtures at 1000 °C. The chemical composition and crystal structure of this new compound were identified by the cross-check combination of first-principles calculations, X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and high resolution scanning transmission electron microscopy (HR-STEM). The stacking sequence of V 2 C and Sn layers results in a crystal structure of space group P6 3 /mmc. The a - and c -lattice parameters, which were determined by the Rietveld analysis of powder XRD pattern, are 0.2981(0) nm and 1.3470(6) nm, respectively. The atomic positions are V at 4f (1/3, 2/3, 0.0776(5)), Sn at 2d (2/3, 1/3, 1/4), and C at 2a (0, 0, 0). A new set of XRD data of V 2 SnC was also obtained. Theoretical calculations suggest that this new compound is stable with negative formation energy and formation enthalpy, satisfied Born-Huang criteria of mechanical stability, and positive phonon branches over the Brillouin zone. It also has low shear deformation resistance c 44 (second-order elastic constant, c ij ) and shear modulus ( G ), positive Cauchy pressure, and low Pugh’s ratio ( G/B = 0.500 < 0.571), which is regarded as a quasi-ductile MAX phase. The mechanism underpinning the quasi-ductility is associated with the presence of a metallic bond.