実験報告書様式（一般利用課題・成果公開利用）

MLF Experimental Report
課題番号 Project No. 2017A0115

提出日 Date of Report
装置責任者 Name of responsible person
Toyoto Sato

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Observation of hydrogen release reaction on a complex hydride

NOVA (BL-21)

実験責任者名 Name of principal investigator

実施日 Date of Experiment

Toyoto sato

2017 June 4 – 7

所属 Affiliation
Tohoku university
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.
Lanthanum magnesium nickel deuteride, LaMg2NiD7, Powder

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

Complex hydrides, which is composed of metal cation(s) such as Mg2+ and complex anion(s) such as [NiH4]4–
with covalent bonding between the central atom and the hydrogen, have attracted due to a wide variety offunctionalities, such as hydrogen storage materials and so on [S. Orimo, et al., Chem. Rev. 107, 4111, (2007).].
Although formation (hydrogenation) and decomposition (hydrogen release) reaction processes of the complex
hydrides are of both fundamental and technological interest in order to further understand such functionalities,
the reaction processes is difficulty in understanding because most of complex hydrides generally show large
rearrangements of metal atomic frameworks during the reactions. In contrast, a complex hydride LaMg2NiH7
composed of La3+, 2×Mg2+, [NiH4]4– and 3×H– is formed from a ternary intermetallic compound LaMg2Ni withmaintaining of the metal atomic frameworks under hydrogen gas pressure (Fig. 1). Focusing on thehydrogenation reaction process from LaMg2Ni to LaMg2NiH7 with maintaining of metal atomic frameworks, werecently discovered an intermediate phase LaMg2NiH4.6 with NiHx units (x = 2 and 3) (Fig. 1), which wasyielded before formation of LaMg2NiH7, by using neutron diffraction experiments combined with theoretical
calculations [K. Miwa, T. Sato et al., J. Phys. Chem. C 120, 5926, (2016).].
1

2. 実験方法及び結果（つづき） Experimental method and results (continued)
The NiHx units showed similar Ni and H atomic
arrangements and covalent bonding of Ni–H to acomplex anion [NiH4]4– in LaMg2NiH7. Thus, thoseunits could be suggested as precursor units for formationof [NiH4]4–. In addition, we could successfully observehydrogenation(deuteration)

reactionprocessofLaMg2Ni viewed from the crystal structure by in–situ
neutron powder diffraction under deuterium gas pressure(≤ 5 MPa) using NOVA (2014A0200) [T. Sato et al., Int.
J. Hydrogen Energy in press]. Though those results
revealed the hydrogenation reaction process ofLaMg2Ni (LaMg2NiH7), the hydrogen release reaction
has been yet to be completely understood.
In this study, we therefore performed powder neutron
diffraction experiments on LaMg2NiD7 upon heating(10–450 K) under vacuum using NOVA (BL–21) for
understandingofdeuterium

releasereactionofLaMg2NiD7. Powder of LaMg2NiD7 (1.1644 g) was
synthesized from LaMg2Ni in D2 pressure of 1 MPa at473 K for 12h and filled in a cylindrical null-scattering
V96Ni4 alloy sample container with an outside diameter

Fig. 1 Crystal structures and local atomic
arrangements around Ni of (top) LaMg2Ni,(middle)
LaMg2NiH4.6and(bottom)
LaMg2NiH7. Gray, orange, green and blue
circles indicate La, Mg, Ni and H,respectively.

and thickness of 6.0 mm and 0.1 mm, respectively.
Rietveld refinement on powder neutron diffraction
patterns was performed using the GSAS software withthe graphical interface EXPGUI (version 1.80).
Figure 2 shows Rietveld refinement fits on the powder
neutron diffraction observed at 10 K. The experimentallyobserved powder neutron diffraction pattern wasreasonably reproduced by a crystal structure ofLaMg2NiD7 with a monoclinic structure with a =13.9839(7) Å, b = 4.6905(2) Å, c = 16.0312(7) Å and β= 125.242(2)° in the space group P21/c (No. 14).
Furthermore, all powder neutron diffraction patterns up
to 450 K were also analyzed by Rietveld refinements.
From the Rietveld refinement results, crystallographic
parameters on LaMg2NiD7 before deuterium releasingchange with increasing temperature. Those results would
relate to deuterium release reaction of LaMg2NiD7.

2Fig. 2 The Rietveld refinement fit of thepowder neutron diffraction for LaMg2NiD7
observed at 10 K (Rwp = 0.0067). The
observed, calculated, background anddifference between observed and calculated
are indicated black circles, a red, green andblue lines, respectively.