Abstract:

Owing to the excellent elastic properties and chemical stability, binary metal or light element borides, carbides and nitrides have been extensively applied as hard and low-compressible materials. Researchers are searching for harder materials all the time. Recently, the successful fabrication of nano-twinned cubic BN (Tian et al. Nature 493:385-388, 2013) and diamond (Huang et al. Nature 510:250-253, 2014) exhibiting superior properties than their twin-free counterparts allows an efficient way to be harder. From this point of view, the borides, carbides and nitrides may be stronger by introducing twins, whose formation tendency can be measured using stacking fault energies (SFEs). The lower the SFEs, the easier the formation of twins. In the present study, by means of first-principles calculations, we first calculated the fundamental elastic constants of forty-two borides, seventeen carbides and thirty-one nitrides, and their moduli, elastic anisotropy factors and bonding characters were accordingly derived. Then, the SFEs of the {111}<112>glide system of twenty-seven compounds with the space group F$\bar{4}$3m or Fm$\bar{3}$m were calculated. Based on the obtained elastic properties and SFEs, we find that (1) light element compounds usually exhibit superior elastic properties over the metal borides, carbides or nitrides; (2) the 5d transition-metal compounds (ReB₂, WB, OsC, RuC, WC, OsN₂, TaN and WN) possess comparable bulk modulus (B) with that of cBN (B=363 GPa); (3) twins may form in ZrB, HfN, PtN, VN and ZrN, since their SFEs are lower or slightly higher than that of diamond (SFE=277 mJ/m²). Our work can be used as a valuable database to compare these compounds.

Key words: Inorganic compounds, Elastic properties, Stacking fault energies, First-principles calculations