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 (K 0) 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 (K 0) 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.
|Журнал||Journal of Physics: Conference Series|
|Состояние||Опубликовано - 31 июл 2020|
|Событие||32nd International Symposium on Superconductivity, ISS 2019 - Kyoto, Япония|
Продолжительность: 3 дек 2019 → 5 дек 2019