Journal
JOURNAL OF ALLOYS AND COMPOUNDS
Volume 348, Issue 1-2, Pages 129-137Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/S0925-8388(02)00797-1
Keywords
hydrogen absorbing materials; metal hydrides; gas-solid reactions; crystal structure; neutron diffraction
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The title compounds have been prepared by induction melting and investigated with respect to structure and hydrogenation properties. Both crystallise with the cubic MgCu4Sn type structure (space group F (4) over bar 3m, LaNi4Mg: a = 7.17-7.18 Angstrom, NdNi4Mg: a = 7.09875(1) Angstrom) and absorb reversibly up to 4 hydrogen atoms per formula unit at 7-8 bar and similar to50 degreesC. Synchrotron and neutron powder diffraction data on deuterated NdNi4Mg indicate an orthorhombic lattice distortion (NdNi4MgD3.6, space group Pmn2(1), a = 5.0767(2), b = 5.4743(2), c = 7.3792(3) Angstrom, DeltaV/V = 14.6%) and three almost fully occupied deuterium sites of which two are coordinated by a trigonal metal bipyramid ([A(2)B(3)] apices: A=2Nd, base: B=2Ni,Mg) and one is coordinated by a metal tetrahedron ([AB(3)] A = Nd, B = 3Ni). The hydride is stable at room temperature under I bar hydrogen pressure, but desorbs rapidly at 80 degreesC under vacuum. Under air it decomposes by catalytic water formation. (C) 2002 Elsevier Science B.V. All rights reserved.
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