Predicted structural evolution and detailed insight into configuration correlation, mechanical properties of silicon–boron binary compounds?

RSC Advances Pub Date: 2017-03-13 DOI: 10.1039/C7RA00592J

Abstract

The crystal structures, phase stability, mechanical and electronic structures of silicon–boron binaries have been investigated systematically using first-principles of pseudopotential calculations. The calculated formation enthalpies of α-SiB3, SiB6 and SiBn follow the sequence: ΔHf (α-SiB3) > ΔHf (SiB6) > ΔHf (SiBn), which is in good agreement with the previous experimental results. Monoclinic SiB6 with P21/m symmetry and hexagonal SiB36 with a B80 unit (a ring linked by diametrically located 2 × B28, 2 × B12) are suggested as the more energetically and mechanically favorable phases by our calculations. The predicted bulk modulus of Si–B binaries is between 120 and 180 GPa, while there is a dramatic drop for two kinds of α-SiB3 in the shear modulus from 130.3 GPa (SiB3) to 71.1 GPa (SiB4). We infer that the additional centered boron atoms, located long the spatial diagonal in SiB4, is responsible for the weakness along this direction. In addition to β-SiB3, the new proposed P21/m-SiB6 and R3m-SiB6 is found to be semiconducting with 0.41 eV indirect and 1.654 eV direct band gap, respectively. There is no band gap provided by band structures of SiB4 and SiB36, as well as their DOS values are quite large at Fermi level, indicating they are energetically unstable under 0 K and GPa.

Graphical abstract: Predicted structural evolution and detailed insight into configuration correlation, mechanical properties of silicon–boron binary compounds
Recommended Literature