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. 2017 Feb 4;10(2):128.
doi: 10.3390/ma10020128.

Exploring the Mechanical Anisotropy and Ideal Strengths of Tetragonal B₄CO₄

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Free PMC article

Exploring the Mechanical Anisotropy and Ideal Strengths of Tetragonal B₄CO₄

Baobing Zheng et al. Materials (Basel). .
Free PMC article

Abstract

First-principles calculations were employed to study the mechanical properties for the recently proposed tetragonal B₄CO₄ (t-B₄CO₄). The calculated structural parameters and elastic constants of t-B₄CO₄ are in excellent agreement with the previous results, indicating the reliability of the present calculations. The directional dependences of the Young's modulus and shear modulus for t-B₄CO₄ are deduced in detail, and the corresponding results suggest that the t-B₄CO₄ possesses a high degree of anisotropy. Based on the strain-stress method, the ideal tensile and shear strengths along the principal crystal directions are calculated, and the obtained results indicate that the shear mode along (001)[100] slip system dominates the plastic deformation of t-B₄CO₄, which can be ascribed to the breaking of the ionic B-O bonds. The weakest ideal shear strength of 27.5 GPa demonstrates that the t-B₄CO₄ compound is not a superhard material, but is indeed a hard material. Based on the atomic explanation that the ternary B-C-O compounds cannot acquire high ideal strength, we propose two possible routes to design superhard B-C-O compounds.

Keywords: B-C-O compound; anisotropic properties; ideal strengths; superhard.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Crystal structures of t-B4CO4 as viewed along the [001] direction (a) and the [010] direction (b), the red, blue, and black spheres represent O, B, and C atoms, respectively.
Figure 2
Figure 2
Orientation dependence of Young’s Modulus E (a,c) and the corresponding projection in the ab, ac, and bc planes (b) for the t-B4CO4, orientation dependence of the shear modulus of t-B4CO4 (d).
Figure 3
Figure 3
Calculated stress-strain relations for t-B4CO4 in various tensile (a) and shear (b) directions.
Figure 4
Figure 4
Structural and ELF transformation before (a) and after (b) the lattice instability for t-B4CO4.
Figure 5
Figure 5
Calculated phonon dispersion curves for t-B4CO4 before (a) and after (b) shear deformation.

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