A first-principles study of uniaxial compression of boron carbide doped by aluminum in intercosahedral chain

Vladyslav Bilyi, Oleksandr Vasiliev

Frantsevich Institute for Problems of Materials Science National Academy of Science of Ukraine


Boron carbide is a widely used impact-resistant ceramic due to its hardness, low density, and high Hugonio elastic limit, but it is prone to amorphization under high non-hydrostatic loads. Fanchini [1] suggested that the cause of amorphization lies in the (B₁₂)C-C-C boron carbide polytype, namely in the intercosahedral C-C-C chain. Previously, we determined [2] that the substitution of aluminum in the center of the chain is possible, and the most likely configuration is (B₁₂)C^Al^C. In this work, we consider the simulation of uniaxial compression along the intercosahedral chain of (B₁₂)C^Al^C and (B₁₂)C-C-C. For both configurations, we calculate the dependence of uniaxial stress on uniaxial strain and determine the maximum uniaxial stress and elastic strain values. We used a slightly modified method of uniaxial compressing that was described in [3]. The simulation was performed using the Quantum Espresso software package. A 2x2x1 unit cells of (B₁₂)C-C-C hexagonal supercell was constructed along the intercosahedral chain. All central carbon atoms were changed to aluminum and shifted in the same direction. Compression simulations were performed with a step size of 0.01 of the uniaxial elastic strain. Parameters used in the calculation include: kinetic energy cutoff for wavefunctions of 100 Ry, convergence criteria of $10^{-6}$ Ry for the self-consistent field and $10^{-3}$ Ry/Bohr for forces on the atoms, gamma point only for Brillouin zone, and gaussian spreading of $10^{-4}$ Ry. Our results show that the introduction of aluminum into the chain of (B₁₂)C-C-C polytype leads to a decrease in the maximum elastic strain (from 0.24 to 0.17) and the maximum uniaxial stress (from 161 GPa to 94 GPa) that the system can withstand.  Consequently, the (B₁₂)C^Al^C configuration has lower mechanical properties compared to the (B₁₂)C-C-C polytype of boron carbide. No mechanism for improving the characteristics of boron carbide was identified.

Keywords
First-principles, Boron carbide, Amorphization, Boron carbide doping

References
[1] G. Fanchini, J. W. McCauley, and M. Chhowalla, ‘Behavior of Disordered Boron Carbide under Stress’, Phys. Rev. Lett., 2006. V. 97, No. 3, P. 035502.
[2] O. Vasiliev, V. Bilyi, Y. Zaulychnyy, and V. Kartuzov, ‘Ground states in B4C-Al system’, presented at the HighMatTech-2023, Kyiv, Ukraine, Oct. 2023.
[3] S. Aryal, P. Rulis, and W. Y. Ching, ‘Mechanism for amorphization of boron carbide B₄C under uniaxial compression’, Phys. Rev. B 2011. V. 84, No. 18, P. 184112.