Prediction of superconductivity in pressure-induced new silicon boride phases

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, B2Si, BSi, and BSi2, 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 B12 icosahedron in the ambient phases to the similar buckled graphenelike layers in the high-pressure phases, which crystalize in the same P3¯m1 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 Tc value of 21 K from the Allen-Dynes equation in P3¯m1 B2Si, which is much higher than the one observed in boron doped diamond-type silicon. Moreover, further fully anisotropic Migdal-Eliashberg calculations indicate that B2Si is a two-gap anisotropic superconductor and the estimated Tc might reach up to 30 K at 1 atm. On the silicon-rich side, BSi2 is predicted to be stable in the CuAl2-type structure. Our current results significantly enrich the phase diagram of the B-Si system and will stimulate further experimental study.

Source-reported materials — not catalogue approval

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