Electronic bonding analyses and mechanical strengths of incompressible tetragonal transition metal dinitrides TMN2 (TM = Ti, Zr, and Hf)

Abstract

Motivated by recent successful synthesis of transition metal dinitride TiN2, the electronic structure and mechanical properties of the discovered TiN2 and other two family members (ZrN2 and HfN2) have been thus fully investigated by using first-principles calculations to explore the possibilities and provide guidance for future experimental efforts. The incompressible nature of these tetragonal TMN2 (TM = Ti, Zr, and Hf) compounds has been demonstrated by the calculated elastic moduli, originating from the strong N-N covalent bonds that connect the TMN8 units. However, as compared with traditional fcc transition metal mononitride (TMN), the TMN2 possess a larger elastic anisotropy may impose certain limitations on possible applications. Further mechanical strength calculations show that tetragonal TMN2 exhibits a strong resistance against (100)[010] shear deformation prevents the indenter from making a deep imprint, whereas the peak stress values (below 12 GPa) of TMN2 along shear directions are much lower than those of TMN, showing their lower shear resistances than these known hard wear-resistant materials. The shear deformation of TMN2 at the atomic level during shear deformation can be attributed to the collapse of TMN8 units with breaking of TM-N bonds through the bonding evolution and electronic localization analyses.

Crystal structures of transition metal pernitrides predicted from first principles

“…To date, VN 2 , ZrN 2 and HfN 2 have not been synthesized. In a previous theoretical study, 23 ZrN 2 and HfN 2 are assumed to have the same ground state structure as TiN 2 since the three TMs are in the same group in the periodic table. Our structure search confirmed this conjecture.…”

“… 7 In addition to the realized pernitrides, many others were predicted to exist as well, await for future synthesis. The long list includes ZrN 2 , 20 CrN 2 , 21 NbN 2 , 22 HfN 2 , 23 WN 2 , 24 and others. 25–27 Several new prototypic structures were proposed for TM pernitrides, including the pyrite-type, P 6 3 / mmc and P 6̄ m 2 structures, some of which were suggested based on the structure analogy with chemically similar materials.…”

ADAIS: Automatic Derivation of Anisotropic Ideal Strength via high-throughput first-principles computations

“…For 3D materials, Table 2 lists the calculated ideal tensile and shear strengths via affine pure deformation of a broad class of materials with different symmetry except triclinic system, together with the previous theoretical values [4,7,27,[49][50][51][52][53] for comparison. It is found that all calculated values by ADAIS code are in reasonable agreement with the previous theoretical values [4,7,27,[49][50][51][52][53], confirming the validity of ADAIS code for 3D materials. Also, Table 3 lists the calculated uniaxial and biaxial tensile strengths of 2D materials with hexagonal and rectangular systems, together with the previous theoretical values [23,54] for comparison.…”

Elastic Properties and Elastic Anisotropy of ZrN2 and HfN2

“…According to the symmetry of crystal, the number of independent elastic constants can be reduced. ZrN 2 and HfN 2 are of tetragonal symmetry, and thus have six independent elastic constants and the elastic stiffness tensor matrix can be expressed in the following way [19]:…”