TY - JOUR
T1 - Crystal structure change in the dehydrogenation process of the Li-Mg-N-H system
AU - Noritake, T.
AU - Aoki, M.
AU - Matsumoto, M.
AU - Miwa, K.
AU - Towata, S.
AU - Li, H. W.
AU - Orimo, S.
N1 - Funding Information:
The synchrotron radiation experiments were carried out on BL19B2 of the SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal Nos. 2005A0152-NI-np, 2005B0897-NI-np). This work was partially supported by the New Energy and Industrial Technology Development Organization (NEDO). The authors express their heartfelt thanks to Mr. G. Kitahara, Ms. N. Ohba and Dr. Y. Nakamori for their valuable support and discussion.
PY - 2011/6
Y1 - 2011/6
N2 - The Li-Mg-N-H system has the property of reversible reaction with hydrogen between hydrogenation and dehydrogenation (Mg3N2 + 4Li3N + 12H2 ↔ 3Mg(NH2)2 + 12LiH). At the several dehydrogenation stages of p-c isotherm measurement at 523 K, the structural change was investigated using the synchrotron X-ray diffraction. There are two regions in p-c isotherm of the Li-Mg-N-H system, i.e. plateau and sloping region. In the plateau region, Mg(NH2) 2 and Li3Mg3(NH2)(NH)4 coexist. In the sloping region, the intermediate phase Li3+3yMg 3(NH2)1-y(NH)4+2y changes continuously from Li3Mg3(NH2)(NH)4 to Li2Mg(NH)2. The chemical composition of the intermediate phase was estimated from the amount of desorbed hydrogen by p-c isotherm and the atomic ratio of Mg and N by Rietveld analysis. The crystal structure of the intermediate phase, Li3+3yMg3(NH 2)1-y(NH)4+2y (space group: I222), was determined. Because all these intermediate structures are similar to anti-CaF2-type, it is deduced that the dehydrogenation process are caused by the diffusion of Li+ to cation sites of Mg(NH 2)2. The analysis of structural change clarified the dehydrogenation process that is accomplished by the diffusion of Li+ and Mg2+ without N atom diffusion.
AB - The Li-Mg-N-H system has the property of reversible reaction with hydrogen between hydrogenation and dehydrogenation (Mg3N2 + 4Li3N + 12H2 ↔ 3Mg(NH2)2 + 12LiH). At the several dehydrogenation stages of p-c isotherm measurement at 523 K, the structural change was investigated using the synchrotron X-ray diffraction. There are two regions in p-c isotherm of the Li-Mg-N-H system, i.e. plateau and sloping region. In the plateau region, Mg(NH2) 2 and Li3Mg3(NH2)(NH)4 coexist. In the sloping region, the intermediate phase Li3+3yMg 3(NH2)1-y(NH)4+2y changes continuously from Li3Mg3(NH2)(NH)4 to Li2Mg(NH)2. The chemical composition of the intermediate phase was estimated from the amount of desorbed hydrogen by p-c isotherm and the atomic ratio of Mg and N by Rietveld analysis. The crystal structure of the intermediate phase, Li3+3yMg3(NH 2)1-y(NH)4+2y (space group: I222), was determined. Because all these intermediate structures are similar to anti-CaF2-type, it is deduced that the dehydrogenation process are caused by the diffusion of Li+ to cation sites of Mg(NH 2)2. The analysis of structural change clarified the dehydrogenation process that is accomplished by the diffusion of Li+ and Mg2+ without N atom diffusion.
KW - Complex hydride
KW - Hydrogen storage materials
KW - Synchrotron radiation
KW - X-ray diffraction
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U2 - 10.1016/j.jallcom.2011.04.079
DO - 10.1016/j.jallcom.2011.04.079
M3 - Article
AN - SCOPUS:79958191486
VL - 509
SP - 7553
EP - 7558
JO - Journal of Alloys and Compounds
JF - Journal of Alloys and Compounds
SN - 0925-8388
IS - 28
ER -