Superhard hexagonal transition metal and its carbide and nitride: Os, OsC, and OsN

Recent experimental findings suggest that the bulk modulus of osmium is comparable to that of diamond. From first principles calculations we examine the compressibility of diamond, Os, OsC, OsN, and OsO2 as well as cubic BN under pressure. We show that Os, OsC, and OsN in the hexagonal structures are less compressible than their cubic phases. The bulk moduli of hexagonal Os, cubic Os, and hexagonal OsC are smaller than that of diamond but larger than cubic BN. Our results indicate that the hexagonal OsC is a promising superhard material.