Exploring the Real Ground-State Structures of Molybdenum Dinitride

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• 作者：Shuyin Yu ; Bowen Huang ; Xiaojing Jia ; Qingfeng Zeng ; Artem R. Oganov ; Litong Zhang ; Gilles Frapper
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：May 26, 2016
• 年：2016
• 卷：120
• 期：20
• 页码：11060-11067
• 全文大小：509K
• 年卷期：0
• ISSN：1932-7455

文摘

Molybdenum dinitride (MoN₂) was recently synthesized at a moderate pressure of 3.5 GPa, and a layered MoS₂-type structure has been proposed. However, our first-principles calculations of thermodynamic, mechanical and dynamical properties suggest that this layered R3m structure is unstable. Therefore, stable structures of MoN₂ at pressures from atmospheric pressure to 100 GPa have been further examined by utilizing a widely adopted evolutionary methodology USPEX for crystal structure prediction. We find that the ground state of the MoN₂ system is a pernitride structure with space group P6₃/mmc which transforms to a P4/mbm phase above 82 GPa. Chemical bonding analysis shows that one could assign MoN₂ as Mo⁴⁺(N₂^4–); i.e., Mo is formally a d² metal, in agreement with the experimental results of Wang et al. The presence of covalent N₂ dumbbells and strong bonding between Mo⁴⁺ and N₂^4– is the source of the superior mechanical properties of these predicted ultra-incompressible MoN₂ pernitrides.