Theoretical Study On The Stabilities And Electronic Properties Of Binary B-S And Ternary H-B-S Systems Under High Pressures

The discovery of new materials has always been one of the most important subjects of physics and chemistry.As a basic physical parameter,pressure has become an effective way to obtain new materials with desirable properties.However,high-pressure experiments usually have long research period,require high experimental costs and harsh experimental conditions.Compared with experiments,computer simulation technology is faster,lower cost,and can exceed the pressure limit of existing experimental technology.Therefore,theoretical calculations are usually at the forefront of high-pressure science,and play an important role in promoting the development of basic science and new materials,such as the breakthrough progress in superconductivity of hydrogen-rich compounds inspired by theoretical calculations.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 we explored the structures,stabilities and electronic properties of binary B-S and ternary H-B-S systems under high pressure based on first-principles calculations.The main contents and results are as follows:Theoretical calculations are carried out about the high-pressure phase diagrams,electronic properties and superconductivity of the binary B-S system.First-principles-based structural predictions are performed to find stable structures of B-S compounds with various compositions B_xS_y(x=1,y=1-5;x=1-5,y=1;x=2,y=3;x=3,y=2)under high pressure(up to 300 GPa).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,B₂S₃ and BS₂,are predicted at low pressures,exhibiting semiconducting and metallic properties,respectively.BS₂ shows a calculated T_c value of 21.9 K at 200 GPa,becoming the first superconductor among bulk binary B-S compounds.Through theoretical calculations we study the high-pressure structures,stabilities and electronic properties of the ternary H-B-S system.Based on advanced structure search technology,phase stabilities of H-B-S ternary compounds,in the pressure range from 0 to200 GPa,are reliably determined.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.On applying pressure,Ama2 HBS undergoes a semiconductor-to-metal electronic transition and even becomes superconducting.As the only stable compound in H-B-S system under pressure,HBS exhibits diverse pressure-related electronic properties.Our work not only enriches the crystal structures,but also put forward a comprehensive understanding of the diverse electronic properties of B-S and H-B-S systems under pressure.