Structure, Relative Stabilities, Physical Properties, and Hardness of Osmium Carbides with Various Stoichiometries: First-Principle Investigations

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• 作者：Li-Ping Ding ; Peng Shao ; Fang-Hui Zhang ; Xiao-Fen Huang ; Tao-Li Yuan
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：September 17, 2015
• 年：2015
• 卷：119
• 期：37
• 页码：21639-21648
• 全文大小：636K
• ISSN：1932-7455

文摘

Using the first-principles calculations, the structural features, mechanical properties, formation enthalpies, electronic properties and hardness of osmium carbides with various stoichometries have been investigated systematically. The structural stability, thermodynamic stability together with mechanical stability show that Re₂N鈥揙s₂C, OsB₂鈥揙sC₂, trigonal P3虆m1 OsC₂, trigonal P3虆m1 OsC₃, orthorhombic Cmmm OsC₄ and Ru₂Ge₃鈥揙s₂C₃ are the most stable structure for each kind of compounds. But, OsB₂鈥揙sC₂ and Ru₂Ge₃鈥揙s₂C₃ are dynamically unstable based on the calculation of phonon dispersion. The formation enthalpies under high pressure indicate that the Re₂N鈥揙s₂C, P3虆m1 OsC₃, Cmmm OsC₄ and Os₂Si₃鈥揙s₂C₃ (P4c2) have structural stabilities in the entire range of pressure. While for OsC₂, there is a high pressure phase transition exists above 40 GPa. In addition, all the studied osmium carbides exhibit metallic behavior and strong covalent bonding. According to the calculated Vicker hardness based on a semiempirical method, we found that the OsC₄ with Cmmm space group has the largest hardness value (28.4 GPa). Combined with its largest shear modulus and Yong鈥檚 modulus, smallest Poission鈥檚 ratio and low B/G ratio, we predict it is a potential superhard material. By the comparison between the crystal structure of OsC₂ and OsC₃, it is found that the increased C鈥揅 bonds in a cell increase their hardness, whereas the ionicity Os鈥揙s bonds are unfavorable.