Structural models of increasing complexity for icosahedral boron carbide with compositions throughout the single-phase region from first principles

We perform first-principles calculations to investigate the phase stability of boron carbide, concentrating on the recently proposed alternative structural models composed not only of the regularly studied B11Cp(CBC) and B12(CBC), but also of B12(CBCB) and B12(B4). We find that a combination of the four structural motifs can result in low-energy electron precise configurations of boron carbide. Among several considered configurations within the composition range of B10.5C and B4C, we identify in addition to the regularly studied B11Cp(CBC) at the composition of B4C two low-energy configurations, resulting in a new view of the B-C convex hull. Those are [B12(CBC)]0.67[B12(B4)]0.33 and [B12(CBC)]0.67[B12(CBCB)]0.33, corresponding to compositions of B10.5C and B6.67C, respectively. As a consequence, B12(CBC) at the composition of B6.5C, previously suggested in the literature as a stable configuration of boron carbide, is no longer part of the B-C convex hull. By inspecting the electronic density of states as well as the elastic moduli, we find that the alternative models of boron carbide can provide a reasonably good description for electronic and elastic properties of the material in comparison with the experiments, highlighting the importance of considering B12(CBCB) and B12(B4), together with the previously proposed B11Cp(CBC) and B12(CBC), as the crucial ingredients for modeling boron carbide with compositions throughout the single-phase region. © 2018 American Physical Society