Crystal structure and phase stability of the ¦µ phase in the Al-Mg-Zn system

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• 作者：Rico Berthold^a ; ^{berthold@cpfs.mpg.de} ; ^{ricoberthold@web.de} ; Guido Kreiner^a ; Ulrich Burkhardt^a ; Stefan Hoffmann^a ; Gudrun Auffermann^a ; Yurii Prots^a ; Enkhtsetseg Dashjav^a ; Altangerel Amarsanaa^a ; Marek Mihalkovic^b
• 关键词：A. Aluminides ; miscellaneous ; A. Ternary alloy systems ; B. Crystal chemistry of intermetallics ; B. Phase diagrams ; E. Ab-initio calculations
• 刊名：Intermetallics
• 出版年：2013
• 出版时间：January, 2013
• 年：2013
• 卷：32
• 期：Complete
• 页码：259-273
• 全文大小：3537 K

文摘

We report on the phase equilibria, the homogeneity range, the crystal and electronic structure of the ¦µ phase in the Al-Mg-Zn system. The homogeneity range is similar at 360?¡ãC and 330?¡ãC and has a wedge-like shape. Al and Zn vary about 13?at. % and Mg maximal 2.5?at. % . The crystal structure has been characterized by X-ray single crystal structure refinement at two compositions Al_23.2Mg_54.6Zn_22.2 ((Al_1.856Mg_0.368Zn_1.776)Mg₄, Z?=?19, oP152, Pbcm, a?=?8.9374(7)??, b?=?16.812(2)??, c?=?19.586(4)??) and Al_17.1Mg_53.4Zn_29.5 (Al_1.368Mg_0.272Zn_2.360)Mg₄, a?=?8.8822(3)??, b?=?16.7741(7)??, c?=?19.4789(8)??). The structure contains four different types of layers stacked along the c axis which can be classified as pentagon-boat, boat, pentagon-triangle and square-triangle tilings. These tilings are decorated by Al and Zn centred icosahedra. The valence band structure can be described by a nearly free electron model except the 3d Zn contributions at lower energy. The large solubility for Al and Zn is caused by substitutional disorder at the icosahedral sites. Total energy calculations indicate, that the homogeneity range at higher temperatures splits up at 0?K into two ordered structures with compositions Al₁₆Mg₅₀Zn₃₄ and Al₁₀Mg₅₀Zn₄₀.