Abstract
The crystal structures and properties of boron-silicon (B-Si) compounds under pressure have been systematically explored using particle swarm optimization structure prediction method in combination with first-principles calculations. Three new stoichiometries, , BSi, and , are predicted to be stable gradually under pressure, where increasing pressure favors the formation of silicon rich B-Si compounds. In the boron-rich compounds, the network of boron atoms changes from icosahedron in the ambient phases to the similar buckled graphenelike layers in the high-pressure phases, which crystalize in the same symmetry but with different numbers of boron layers between adjacent silicon layers. Phonon calculations show that these structures might be retained to ambient conditions as metastable phases. Further electron-phonon coupling calculations indicate that the high-pressure phases of boron-rich compounds might superconduct at 1 atm, with the highest value of 21 K from the Allen-Dynes equation in , which is much higher than the one observed in boron doped diamond-type silicon. Moreover, further fully anisotropic Migdal-Eliashberg calculations indicate that is a two-gap anisotropic superconductor and the estimated might reach up to 30 K at 1 atm. On the silicon-rich side, is predicted to be stable in the -type structure. Our current results significantly enrich the phase diagram of the B-Si system and will stimulate further experimental study.
- Received 23 October 2019
DOI:https://doi.org/10.1103/PhysRevB.101.014112
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