Phase diagrams and electronic properties of B-S and H-B-S systems under high pressure

Abstract

Pressure has become an effective way to obtain new materials with desirable properties. Considering the various stoichiometries, wide applications, and unique structures of binary H-S, H-B, and B-S compounds, especially at high pressures, it is worth expecting that they might form ternary compounds with interesting properties as well. Here, phase stabilities of H-B-S ternary compounds, in the pressure range from 0 to 200 GPa, are reliably determined through first-principles unbiased structural search calculations. A hitherto unknown orthorhombic HBS compound with Ama2 symmetry is identified to be stable above 25 GPa, in which B and S atoms alternate to form distorted chains and H atoms are covalently bonded with Bs. With pressure, Ama2 HBS undergoes a semiconductor-to-metal electronic transition and even becomes superconducting. The exploration of the binary B-S phase diagram indicates that B-S compounds tend to decompose into elemental solids above 208 GPa. However, two S-rich phases, B 2 S 3 and BS 2 , are predicted at low pressures, exhibiting semiconducting and metallic properties, respectively. BS 2 shows a calculated T c value of 21.9 K at 200 GPa, becoming a superconductor among bulk binary B-S compounds.

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