Crystal structure, layer defects, and the origin of plastic deformability of Nb₂Co₇

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• 作者：A. Leineweber^a ; ^{a.leineweber@is.mpg.de} ; G. Kreiner^b ; D. Grü ; ner^b ; R. Dinnebier^c ; F. Stein^d
• 关键词：A. Intermetallics ; miscellaneous ; B. Crystallography ; D. Defects ; planar faults ; F. Diffraction (electron ; neutron and X-ray)
• 刊名：Intermetallics
• 出版年：2012
• 期刊代码：36_09669795
• 类别：ms
• 出版时间：June, 2012
• 卷：25
• 期：Complete
• 页码：34-41
• 文件大小：1310 K

摘要

The crystal structure of Nb₂Co₇ was identified on the basis of X-ray powder-diffraction data recorded by synchrotron radiation to be of the Zr₂Ni₇ type having monoclinic C2/m symmetry and Pearson symbol mC18 with lattice parameters a聽=聽4.5874(2) 脜, b聽=聽8.1509(4) 脜, c聽=聽6.2223(3) 脜 and 尾聽=聽107.181(3)掳. Fractional coordinates were determined on the basis of Rietveld-refinement methods and geometrical considerations. The structure can be described by stacking of certain extended layer sandwiches parallel to (001). Each of these extended layer sandwiches consists of a central Kagom茅 layer composed of Co atoms only, which is sandwiched by two close-packed layers consisting of Co and Nb atoms. The occurrence of Warren peaks as well as of line broadening is attributed to a stacking disorder of adjacent layer extended sandwiches in the investigated specimen. The unexpected plastic deformability of the intermetallic compound Nb₂Co₇ can be related to specific features of the layered structure model, which provides a glide plane parallel to (001).