An in situ neutron diffraction study of the thermal disproportionation of the Zr2FeD5 system
作者:M.P. Pitt、L.K.W. Pitt、H. Fjellvåg、B.C. Hauback
DOI:10.1016/j.jallcom.2011.02.129
日期:2011.5
The Zr2FeD5 system has been annealed to 680 degrees C under ultra high vacuum, and studied in situ by neutron diffraction. The system disproportionates through three distinct regions in temperature. Initially, the tetragonal Zr2FeD5 (P4/ncc) is retained up to 330 degrees C, while steadily depleted of D. From 330 degrees C to 530 degrees C, a complex multi-phase disproportionation occurs, with the production of cubic ZrD2, tetragonal ZrD2, tetragonal Zr2FeD5 (I4/mcm), and growth of the intermetallic ZrFe2. At the beginning of the 330-530 degrees C period, the total atom count from quantitative phase analysis (QPA) indicates the formation of amorphous (a-) Zr56Fe44. By 530 degrees C, QPA and peak breadth analysis indicate that ca. 2/3rd of the sample is consumed as very small nanocrystals (< 150 angstrom coherence length) of strained ZrD2. From 530 degrees C to 680 degrees C, the cubic ZrD2 is almost entirely consumed and depleted of D to form the final mixture of the intermetallic phases Zr3Fe and ZrFe2. QPA of the final intermetallic mixture yields a Zr:Fe ratio greater than that observed in either the arc melted alloy or the initial Zr2FeD5 deuteride, indicating that a ca. Zr71Fe29 amorphous component was present in the initial arc melted alloy. According to the total atom count by QPA, crystallisation of the Fe richer amorphous Zr56Fe44 phase formed at 330 degrees C begins at ca. 530 degrees C, and later by 680 degrees C, all amorphous phases have completely crystallised to yield a 70.77:26.75:2.47 mol.% mixture of Zr3Fe: ZrFe2: ZrD2-x. (C)2011 Elsevier B. V. All rights reserved.