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. 2016 Aug 25;9(9):726.
doi: 10.3390/ma9090726.

Mechanical and Electronic Properties of XC₆ and XC12

Qun Wei  1 , Quan Zhang  2 , Meiguang Zhang  3
Affiliations

Mechanical and Electronic Properties of XC₆ and XC12

Qun Wei et al. Materials (Basel). .

Abstract

A series of carbon-based superconductors XC₆ with high Tc were reported recently. In this paper, based on the first-principles calculations, we studied the mechanical properties of these structures, and further explored the XC12 phases, where the X atoms are from elemental hydrogen to calcium, except noble gas atoms. The mechanically- and dynamically-stable structures include HC₆, NC₆, and SC₆ in XC₆ phases, and BC12, CC12, PC12, SC12, ClC12, and KC12 in XC12 phases. The doping leads to a weakening in mechanical properties and an increase in the elastic anisotropy. C₆ has the lowest elastic anisotropy, and the anisotropy increases with the atomic number of doping atoms for both XC₆ and XC12. Furthermore, the acoustic velocities, Debye temperatures, and the electronic properties are also studied.

Keywords: carbides; elastic anisotropy; first-principles calculations; mechanical properties.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Unit cell of XC6 (a) and XC12 (b). The black and blue spheres represent C and X atoms, respectively.
Figure 2
Figure 2
Formation enthalpy of XC6 and XC12.
Figure 3
Figure 3
Phonon spectra of dynamically stable phases (a) BC12; (b) CC12; (c) PC12; (d) SC12; (e) ClC12; and (f) KC12.
Figure 4
Figure 4
Phonon spectra of dynamically unstable phases (a) LiC12; (b) BeC12; (c) MgC12; and (d) AlC12.
Figure 5
Figure 5
2D representations of Poisson’s ratio. (a) Maximum of C6 and XC6 stable phases; (b) minimum positive of C6 and XC6 stable phases; (c) maximum of XC12 stable phases; and (d) minimum positive and minimum negative of XC12 stable phases; particularly, only SC12 and ClC12 have the negative minimum Poisson’s ratio, the solid and dash lines represent the minimum positive and minimal negative, respectively.
Figure 6
Figure 6
Directional dependence of the Young’s modulus of C6 (a); HC6 (b); NC6 (c); and SC6 (d).
Figure 7
Figure 7
Directional dependence of the Young’s modulus of BC12 (a); CC12 (b); PC12 (c); SC12 (d); ClC12 (e); and KC12 (f).
Figure 8
Figure 8
Electronic band structure and density of state of BC12 (a); CC12 (b); PC12 (c); SC12 (d); ClC12 (e); and KC12 (f).
Figure 8
Figure 8
Electronic band structure and density of state of BC12 (a); CC12 (b); PC12 (c); SC12 (d); ClC12 (e); and KC12 (f).
Figure 8
Figure 8
Electronic band structure and density of state of BC12 (a); CC12 (b); PC12 (c); SC12 (d); ClC12 (e); and KC12 (f).
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