First-Principle Study Of Structure And Superconductivity Of BC₃

Superhard materials are popular in modern engineering, semiconductor industry and high-tech fields. Now the superhard materials are mainly diamond and cubic BN. But diamond has a poor heat resistance and reacts with the iron-based materials. And the hardness of cubic BN is lower than that of diamond. The shortcomings of these materials limited their application. Furthermore, two kinds of materials are semiconductors, thus limiting their application on electrical conductivity, and therefore people have been searching for more excellent superhard multifunctional materials.Boron-doped diamond maintains strong covalent bond of diamond and introduces metallicity at the same time, making it become a potential superhard multifunctional material. The superconductivity of boron-doped diamond has also been confirmed in theory. But now the study of boron-doped diamond were mainly concentrated in low concentrations (B accounted for 0.02-0.06%) conditions, the boron-rich conditions were few studied. The mechanism of superconductivity of boron-doped diamond and the impact of boron atom stations for the superconductivity in boron-doped diamond are not very clear. Therefore we have designed a tetragonal diamond-like BC3 structure with space group P-4M2. This polymorph, which we call s-BC3, was a boron-doped diamond with boron contents of 25%. It is stable over experimental graphitic-like BC3 above 10 GPa. A striking feature of this structure is the presence of soft modes in the phonon band structure induced by Fermi surface nesting that lead to very strong electron-phonon coupling. The critical temperature of this polymorph is calculated to be 34K, which is comparable to that of MgB2. Furthermore, the hardness of this polymorph is 46 GPa, so the s-BC3 can be seen as a potential superhard material. The research on s-BC3 is of great importance in view of its potential application as a superhard superconducting material.