Mechanical properties and chemical bonding of the Os-B system: A first-principles study

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• 作者：Zong-Wei Ji^a ; Chao-Hao Hu^a ; ^{chaohao.hu@guet.edu.cn} ; Dian-Hui Wang^a ; Yan Zhong^a ; Jiong Yang^b ; Wen-Qing Zhang^b ; Huai-Ying Zhou^a
• 关键词：Mechanical properties ; Os&ndash ; B system ; Superhard material ; First-principles calculations
• 刊名：Acta Materialia
• 出版年：2012
• 期刊代码：1_13596454
• 类别：ms
• 出版时间：June, 2012
• 卷：60
• 期：10
• 页码：4208-4217
• 文件大小：1017 K

摘要

The mechanical properties of Os-B compounds containing different boron contents have been investigated systemically by first-principles calculations. Two previously unreported crystal structures of Os₂B₅ and OsB₃, crystallizing in space groups R3m and P-6m2 respectively, are determined using the ab initio evolutionary structure prediction. The calculated elastic constants, bulk modulus, shear modulus, Young鈥檚 modulus, Poisson鈥檚 ratio, and hardness for Os-B compounds are in good agreement with the available experimental values. Our results show that the hardness of osmium borides increases with increasing boron content. Os₂B₅ and OsB₃, with hardnesses of 34.4 and 36.9 GPa respectively, can almost be considered as potential superhard materials. Further analyses on density of states, crystal orbital Hamilton population, and electron localization function demonstrate that the electronic structure of Os-B compounds is directly responsible for their particular mechanical properties. High hardness in Os₂B₅ and OsB₃ is mainly attributed to the occurrence of strong B-B covalent bonds and the disappearance of some ductile Os-Os metallic bonds.