The effect of structure and phase transformation on the mechanical properties of Re₂N and the stability of Mn₂N

Abstract

First-principles calculations were carried out on recently synthesized Re₂N and Re₃N as well as hypothetical Tc and Mn nitrides. It is found that structure and covalent bonds play an important role in determining mechanical properties. Under a large strain along (0001)<1010> direction, Re₂N undergoes a phase transformation with a slight increase in ideal shear strength. On the other hand, it is transformed into a phase with weaker mechanical properties, if the strain is along Re₂ <1210> direction. Mn₂N can be synthesized under moderate conditions due to its more negative formation energy. Re₂N, Re₃N, and Mn₂ N show structure-related mechanical property under larger strains to ReB₂ but exhibit much lower ideal strengths, which is attributed to the larger ionicity of cation-anion bond. Three-dimensional framework of strong covalent bonds is thus highly recommended to design superhard materials.

Ideal stoichiometric technetium nitrides under pressure: A first-principles study

“…For Tc subnitrides, evolutionary algorithm confirmed that the structures of Tc 3 N and Tc 2 N are isomorphic to Re 3 N and Re 2 N, which form in hexagonal structure within space groups (SG) P 6 m2 and P6 3 /mmc, respectively. This result is consistent with the conclusions of Weck et al [11] and Do et al [12] that Tc subnitrides following the structures of Re subnitrides can be stable. For N-rich Tc nitrides, the proposed stable structures of Tc nitrides are schematically showed in Fig.…”

“…The calculated lattice parameters, cell volume, and N-N bond-length were listed in Table 1. Our calculated lattice parameters are in good accordance with the earlier studies [11,12], proving the reliability of our calculations. Thermodynamic and dynamic stability Thermodynamic stability of materials can be estimated from the formation enthalpy, which is a good approximation of the zero-temperature phase diagram.…”

“…Most recently, Wang et al [10] investigated 10 candidate structures for Tc mononitride and indicated that NiAs-type and NbO-type TcN are more energetically preferred. Recently, Tc subnitrides (Tc 3 N and Tc 2 N) based on the structures of Re subnitrides were also studied theoretically by Weck et al [11] and Do et al [12]. However, compound can actually embody complex mixture ratios depending on the synthetic pathways, and previously investigated ratios of Tc nitrides (Tc 3 N, Tc 2 N, and TcN) were insufficient for providing a comprehensive reference to experimental synthesis and physical applications, while the structure searching methodology, such as USPEX code [13][14][15] might be a good answer to this problem, for its great ability in searching possible structures only naming the elements in a compound.…”

Chemical looping of metal nitride catalysts: low-pressure ammonia synthesis for energy storage

“… 65 Hence, transition metal nitrides, including Mn 2 N, are typically modeled without a Hubbard U correction. 23 , 66 Verifying this and assessing the use of GGA + U methods for metal nitride surfaces is an important point. In a prospective article, we will show how adsorption energies respond to the value of U only for metal compounds that possess a (pseudo) band gap.…”

Nitrogen concentration driving the hardness of rhenium nitrides

“…at moderate pressures (13–20 GPa) and temperatures (1600–2400 K). The ultra-high bulk modulus of > 400 GPa made them novel ultra-incompressible materials1011121314151617. However, independent theoretical works by Zhang et al 18.…”