An in situ neutron diffraction study of the thermal disproportionation of the Zr2FeD5 system

The Zr2FeD5 system has been annealed to 680 °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 °C, while steadily depleted of D. From 330 °C to 530 °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 °C period, the total atom count from quantitative phase analysis (QPA) indicates the formation of amorphous (a-) Zr56Fe44. By 530 °C, QPA and peak breadth analysis indicate that ca. 2/3rd of the sample is consumed as very small nanocrystals (<150 Å coherence length) of strained ZrD2. From 530 °C to 680 °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 °C begins at ca. 530 °C, and later by 680 °C, all amorphous phases have completely crystallised to yield a 70.77:26.75:2.47 mol.% mixture of Zr3Fe:ZrFe2:ZrD2−x.

► Thermal disproportionation of classic tritium getter Zr2FeD5.
► In situ neutron diffraction, accurate quantitative phase analysis.
► Three distinct regions in temperature showing complex phase interactions.
► Production/crystallisation of amorphous Zr1−xFex phases.