Neutron Diffraction Studies of Zr₂NiH(D)_x Hydrides*

In situ powder synchrotron and neutron diffraction study of Zr2Ni deuterides

“…The occupancy of the 16l site shows an increasing tendency with increasing temperature and decreasing deuterium content. These site preference trends fit well with those observed at room temperature for samples with different nominal compositions [5] and the unpublished structure of fully ordered Zr 2 NiD 4.5 [14]. The results are compared in Fig.…”

“…Powder neutron diffraction revealed several peaks that could not be indexed according to the triclinic unit cell. This indicates deuterium ordering in agreement with earlier observations [5]. A full description of the superstructure, which is fully ordered, will be published separately [14].…”

“…9; the open symbols represent data from Ref. [5] whereas the filled symbols are the present values. Values refined from high temperature data are marked with an asterisk (*).…”

“…Squares: 16l sites, triangles: 4b sites, circles: 32m sites. Filled symbols: from the present work, open symbols: from Chikdene et al[5], partly filled: from Elcombe et al[6]. Symbols marked with an asterisk (*) represent samples at elevated temperatures.…”

“…Zr 2 Ni, which forms hydrides with maximum hydrogen content corresponding to about Zr 2 NiH 5 , is the only known exception. Chikdene et al noted some unindexed reflections in the PND pattern for Zr 2 NiD 4.8 , which was proposed to originate from an orthorhombic supercell with doubled a-and c-axis due to deuterium ordering [5]. These ordering peaks disappeared on heating to 420 K. Later, Elcombe et al found from PND and SR-PXD that Zr 2 NiD 4.2 is slightly monoclinically distorted (a ≈ b = c, β = 91 • , space group I2/c) [6].…”