Brittle failure of beta- and tau-boron: Amorphization under high pressure

作者：An Qi; Morozov Sergey I

来源：Physical Review B, 2017, 95(6): 064108.

DOI：10.1103/PhysRevB.95.064108

Element boron tends to form an icosahedral motif involving 26 electrons, leading to intriguing bonding conditions which complicate understating the structural variations under high pressure. Here we used density function theory (DFT) to examine the mechanical response of beta- and recent discovered tau-boron to shear along the most plausible slip system. We found that the failure mechanism of beta-B-106 is fracturing a B-28 triply fused icosahedral cluster without destroying a regular B-12 icosahedron, while the failure of tau-B-106 arises from the disintegration of a B-28 cluster and one nearby icosahedron. The failure of beta-B-106 leads to a B-12-embedded amorphous structure which transforms to the second amorphous phase with a fully deconstructed icosahedra at 81 GPa. The second amorphous phase retains the deconstructed icosahedra at ambient conditions which is different from the normal amorphous boron containing regular icosahedra which are bonded randomly to each other. The second amorphous phase is more stable than beta-B-106 above 90 GPa, which explains the previous experiments on pressure-induced amorphization. In addition, forming the second highest density amorphous phase likely causes the brittle failure of beta-B and related materials.

• 出版日期2017-2-17