First-principles study on the structure, elastic properties, hardness and electronic structure of TMB4 (TM=Cr, Re, Ru and Os) compounds

Abstract

The structural formation, elastic properties, hardness and electronic structure of TM B 4 ( TM =Cr, Re, Ru and Os) compounds are investigated using first-principles approach. The value of C 22 for these compounds is almost two times bigger than the C 11 and C 33 . The intrinsic hardness, shear modulus and Young's modulus are calculated to be in a sequence of CrB 4 >ReB 4 >RuB 4 >OsB 4 , and the Poisson's ratio and B / G ratio of TM B 4 follow the order of CrB 4 <ReB 4 <RuB 4 <OsB 4 . The intrinsic hardness of CrB 4 and ReB 4 by LDA is bigger than 40 GPa. The high hardness of TM B 4 compounds is derived from the feature of B–B bonds cage and higher C 22 value. The B–B covalent bonds as bonds cage enhances the resistance to shear deformation and improve the hardness. We predict that the TM B 4 compounds with CrB 4 -type are the potential superhard materials. The first-principles calculations show that the intrinsic hardness of CrB 4 and ReB 4 are bigger than 40 GPa, which are the potential superhard materials due to the B–B bonds cage structure. • The intrinsic hardness of CrB 4 and ReB 4 is bigger than 40 GPa. • The hardness of TM B 4 is calculated to be in a sequence of CrB 4 >ReB 4 >RuB 4 >OsB 4 . • The trend of hardness for TM B 4 is consistent with the variation of elastic modulus. • The C 22 value of TM B 4 is bigger than that of C 11 and C 33 . • The high hardness of TM B 4 is originated from the B–B bonds cage.