実験報告書様式（一般利用課題・成果公開利用）
提出日 Date of Report

MLF Experimental Report
課題番号 Project No.

装置責任者 Name of responsible person

2014A0200

Otomo Toshiya

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Formation and Decomposition Processes of Metal-Deuterium Bonds between LaMg2NiNOVA (BL21)

and LaMg2NiD7 Studied by in-situ Powder Neutron Diffraction

実施日 Date of Experiment

実験責任者名 Name of principal investigator2014 May 29- June 02

Toyoto Sato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, LaMg2Ni, 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.

LaMg2Ni has been reported to form LaMg2NiH7 ina hydrogen gas pressure of 0.8 MPa at 473 K [Phys. Rev.
Lett. 94 (2005) 066403.]. Figure 1 shows crystal
structures of LaMg2Ni and LaMg2NiH7. Although bothcompounds have different crystal systems (LaMg2Ni:
orthorhombic (a = 4.227 Å, b = 10.303 Å, c = 8.360 Å;
LaMg2NiH7: monoclinic (a = 13.979 Å, b = 4.703 Å,

c = 16.025 Å, β = 125.240º)), they adopt similar
frameworks of metal atomic arrangements. In theframeworks, LaMg2NiH7 show slightly distorted fromLaMg2Ni as typical interstitial-type hydrides in whichhydrogen atoms are located at interstitial sites

Figure 1 Crystal structures ofsurrounded by metal atoms.

(top) LaMg2Ni and (bottom) LaMg2NiH71

2. 実験方法及び結果（つづき） Experimental method and results (continued)
On the contrary, LaMg2NiH7 is not classified into the interstitial-type hydrides because it interestingly has
two different kinds of hydrogen – metal interactions which are tetrahedral [NiH4]4- complex anion (H atoms arecovalently bonded with Ni atom) and H- (H atom is surrounded by Mg and La atoms). Even though many typesof hydrides have been reported, coexistence of such two different kinds of the bonding state associated withhydrogen is in rare cases.
For the reason, this is one good hydride for understanding of the bonding state associated with hydrogen.
Though researchers have clarified the hydrogen absorption and desorption properties and crystal andelectronic structures and materials properties on LaMg2NiH7 [K. Yvon et al., Phys. Rev. Lett. 94 (2005)066403.; M.D. Chio, et al., intermetallics 16 (2008) 102.; A. Teresiak et al., J. Alloys Compd. 481 (2009) 144.],
the formation process of the hydride from the viewpoint of the interaction between metal and hydrogen has
not been reported in spite of indispensable for development of hydrogen storage materials.
Therefore, we have carried out the in-situ neutron diffraction experiments on LaMg2Ni in deuterium
atmosphere at NOVA (BL-21) in order to elucidate the formation processes of the two different bonding
states associated with deuterium in LaMg2NiD7.
Approximately 2.0 g of LaMg2Ni, which was synthesized by an induction furnace, was placed in a quartz
container with an inside diameter of 6 mm for the neutron diffraction experiments. In our preliminary
experiment at our laboratory, LaMg2Ni quickly formed LaMg2NiH7 at 473 K in the hydrogen gas pressure of 1MPa. The quick hydrogenation reaction was guessed to prevent from elucidation of the hydrogenation
reaction. However, LaMg2Ni gradually showed hydrogenation reaction and formed LaMg2NiH7 at room
temperature in a hydrogen atmosphere. Therefore, the neutron diffraction experiments were carried out at 303
K in a deuterium gas pressure of ≤ 5 MPa.
Figure 2 shows the neutron diffraction patterns before
and after deuteration reaction of LaMg2Ni with asimulated neutron diffraction pattern of LaMg2NiD7. The
neutron diffraction pattern indicates that LaMg2Ni surelyformed LaMg2NiD7 at room temperature in a deuterium
atmosphere. This is that [NiH4]4- complex anion wasformed at room temperature. In addition, minor unknown
peaks are also identified. Presently, the neutron
diffraction patterns are analyzed by Rietveld method[R. Oishi et al., Nucl. Instrum. Methods A 600 (2009) 94.]
in order to elucidate the unknown phase and theformation processes of LaMg2NiD7 from LaMg2Ni.
The dehydrogenation (hydrogen release reaction) ofLaMg2NiD7 showed at around 523 K in vacuum and LaDx

Figure 2 Neutron diffraction patterns of LaMg2Niand Mg2Ni were yielded.

In vacuum (0.0001 MPa) and a deuterium gas
pressure of 5 MPa and simulated neutron
diffraction pattern of LaMg2NiD72