The search for the new superconductors in the Ni-N system

• Published in: Journal of physics. Conference series 2020-07, Vol.1590 (1), p.12010
• Main Authors: Gavryushkin, P N, Sagatov, N, Sagatova, D, Banaev, M V, Donskikh, K G, Litasov, K D
• Format: Article
• Language: English
• Subjects: Bulk modulus; Crystal structure; Hydrides; Interstitial compounds; Iron; Mechanical properties; Metal nitrides; Nickel compounds; Nitrogen; Physics; Pyrite; Superconductivity; Superconductors; Transition metals
• ISSN: 1742-6588; 1742-6596
• DOI: 10.1088/1742-6596/1590/1/012010

Transition metal nitrides show a unique combination of superconducting and mechanical properties. In this study we perform a theoretical search of the intermediate compounds in Ni-N system, determine their superconducting transition temperatures (Tc) and bulk moduli (K0) in the wide range of pressures, from 0 to 300 GPa. We have revealed several nickel-rich interstitial compounds, Ni5N2, Ni3N, and Ni6N, and one nitrogen-rich compound, NiN2, as stable structures. At pressures above 100 GPa, previously unknown NiN with anti-nickeline structure is also stabilized. All found compounds are non-magnetic. The most promising for superconductivity NiN2 structure is stable against decomposition on the mixture of (Ni+N) from 3 to at least 300 GPa. The transition from marcasite-type NiN2-Pnnm to pyrite-type NiN2-Pa3¯ occurs at 70 GPa. NiN2-Pnnm is an insulator with the band gap of about 1 eV, while NiN2-Pa3¯ is a metallic phase. The calculated Tc of NiN2-Pnnm equals to 10−2 K, and the bulk modulus (K0) equals to 225 GPa at 10 GPa, which is in excellent agreement with available experimental data. The comparison of Tc of compounds in the Ni-H and Ni-N systems with that of the Fe-H and Fe-N compounds, shows that hydrides and nitrides of nickel have lower Tc than hydrides and nitrides of iron, which is explained by the significant differences in crystal structures.