Abstract
We have explored the mechanical properties, electronic structures and phase transition behaviors of three designed new phases for element boron from ambient condition to high-pressure of 120 GPa including (1) a C2/c symmetric structure (m-B16); (2) a symmetric structure (c-B56) and (3) a Pmna symmetric structure (o-B24). The calculation of the elastic constants and phonon dispersions shows that the phases are of mechanical and dynamic stability. The m-B16 phase is found to transform into another new phase (the o-B16 phase) when pressure exceeds 68 GPa. This might offer a new synthesis strategy for o-B16 from the metastable m-B16 at low temperature under high pressure, bypassing the thermodynamically stable γ-B28. The enthalpies of the c-B56 and o-B24 phases are observed to increase with pressure. The hardness of m-B16 and o-B16 is calculated to be about 56 GPa and 61 GPa, approaching to the highest value of 61 GPa recorded for α-Ga-B among all available Boron phases. The electronic structures and bonding characters are analyzed according to the difference charge-density and crystal orbital Hamilton population (COHP), revealing the metallic nature of the three phases.
Highlights
Phase transitions, mechanical properties and electronic structures of novel boron phases under high-pressure: A first-principles study
We have explored the mechanical properties, electronic structures and phase transition behaviors of three designed new phases for element boron from ambient condition to high-pressure of 120 GPa including (1) a C2/c symmetric structure (m-B16); (2) a Ia3 symmetric structure (c-B56) and (3) a Pmna symmetric structure (o-B24)
The schematic ambient crystal structure of the first new phase is shown in Figure 1, suggesting an orthorhombic structure with the space group Pmna
Summary
Mechanical properties and electronic structures of novel boron phases under high-pressure: A first-principles study. Pickard et al.[8] obtained a new metastable phase by an ab initio random structure searching method and this new phase can be viewed as a polymorph of a-B, differing in the connectivity of the icosahedral www.nature.com/scientificreports units and just 0.01 eV/atom less stable. He et al.[31] subsequently studied the properties of this phase (termed a*-B) by first-principles calculations. The a-Ga structure and its variants of boron stimulate great interest in probing the high-pressure phase[5,18,32]
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