The electronic, mechanical and thermodynamic properties of Fe–N binary compounds under 330 GPa: First-principle calculations

The structural, elastic and thermodynamic properties of Fe–N binary compounds have been investigated using the first-principle calculation. Fe8N, Fe4N, Fe2N, Fe3N2 FeN and FeN2 have been optimized and calculated under 330 GPa. Their mechanical stability has been verified by Born stable criterion. Firstly, the content of N will not change the conductivity of Fe–N binary compounds. And when the proportion of Fe and N become 1: 2, the electrons will gather to Fermi's level. It may be concluded that light element N is able to change the electronic structure of Fe–N binary compounds from the results of electronic properties. Secondly, mechanical properties, including Young's modulus E, Poisson's ratio σ, B/G, anisotropy and Vickers hardness, are calculated by elastic constants. E and Vickers hardness decrease with the rising content of N in Fe–N compound. However, when N becomes the main element in Fe–N binary compound, the varying tendency change conversely. Particularly, Fe2N has the lowest E and Vickers hardness, approximately 902.90 GPa and 54 GPa respectively. On the contrary, the varying trend of σ is opposite, and Fe2N has the highest σ, 0.40. According to the B/G, Fe–N compound presents an excellent ductility, especially FeN2. Moreover, all of structures remains elastic anisotropy. Finally, thermodynamic properties, including Debye temperature θD and minimum thermal conductivity kmin, increase with the rising content of N in Fe–N binary compound. Ultimately, FeN has a lower Tm compared with pure Fe under inner core pressure. It means that adding N into Fe is able to decrease the Tm of pure Fe.