Phase Relations and Crystal Structure of 蟿6-Ti2(Ti0.16Ni0.43Al0.41)3

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• 作者：Atta U. Khan ; A. Grytsiv ; X. Yan ; P. Rogl ; A. Saccone ; V. Pomjakushin ; G. Giester
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：May 16, 2011
• 年：2011
• 卷：50
• 期：10
• 页码：4537-4547
• 全文大小：1264K
• 年卷期：v.50,no.10(May 16, 2011)
• ISSN：1520-510X

文摘

Ti₂(Ti_0.16Ni_0.43Al_0.41)₃ is a novel compound (labeled as 蟿₆) in the Ti-rich region of the Ti鈭扤i鈭扐l system in a limited temperature range 870 < T < 980 掳C. The structure of 蟿₆-Ti₂(Ti,Ni,Al)₃ was solved from a combined analysis of X-ray single crystal and neutron powder diffracton data (space group C2/m, a = 1.85383(7) nm, b = 0.49970(2) nm, c = 0.81511(3) nm, and 尾 = 99.597(3)掳). 蟿₆-Ti₂(Ti,Ni,Al)₃ as a variant of the V₂(Co_0.57Si_0.43)₃-type is a combination of slabs of the MgZn₂-Laves type and slabs of the Zr₄Al₃-type forming a tetrahedrally close-packed Frank鈭扠asper structure with pentagon鈭抰riangle main layers. Titanium atoms occupy the vanadium sites, but Ti/Ni/Al atoms randomly share the (Co/Si) sites of V₂(Co_0.57Si_0.43)₃. Although 蟿₆ shows a random replacement on 6 of the 11 atom sites, it has no significant homogeneity range (1 at. %). The composition of 蟿₆ changes slightly with temperature. DSC/DTA runs (1 K/min) were not sufficient to define proper reaction temperatures due to slow reaction kinetics. Therefore, phase equilibria related to 蟿₆ were derived from X-ray powder diffraction in combination with EPMA on alloys, which were annealed at carefully set temperatures and quenched. 蟿₆ forms from a peritectoid reaction 畏-(Ti,Al)₂Ni + 蟿₃ + 伪₂ 鈫?蟿₆ at 980 掳C and decomposes in a eutectoid reaction 蟿₆ 鈫?畏 + 蟿₄ + 伪₂ at 870 掳C. Both reactions involve the 畏-(Ti,Al)₂Ni phase, for which the atom distribution was derived from X-ray single crystal intensity data, revealing Ti/Al randomly sharing the 48f- and 16c-positions in space group Fd3̅m (Ti₂Ni-type, a = 1.12543(3) nm). There was no residual electron density at the octahedral centers of the crystal structure ruling out impurity stabilization. Phase equilibria involving the 蟿₆ phase have been established for various temperatures (T = 865, 900, 925, 950, 975 掳C, and subsolidus). The reaction isotherms concerning the 蟿₆ phase have been established and are summarized in a Schultz鈭扴cheil diagram.