L Journal of Alloys and Compounds 279 (1998) L4–L7 Letter Hydrogen sorption properties of intermetallic TbNiAl and crystal structure of TbNiAlD 1.1 a ,b , 1 ,c c d a ,e e f * V.A. Yartys , F. Gingl , K. Yvon , L.G. Akselrud , A.V. Kolomietz , L. Havela , T. Vogt , g b I.R. Harris , B.C. Hauback a Metal Hydrides Department, Karpenko Physico –Mechanical Institute of the National Academy of Sciences of Ukraine, 5, Naukova Str., Lviv, 290601, Ukraine b Institute for Energy Technology, P .O.Box 40, Kjeller, N-2007, Norway c ´ ` ` Laboratoire de Cristallographie, Universite de Geneve, 24 quai Ernest Ansermet, CH-1211 Geneve 4, Switzerland d Institute of Inorganic Chemistry, Lviv State University, 6, Kyryla and Mefodiya Str., Lviv, Ukraine e Department of Metal Physics, Charles University, 5, Ke Karlovu, 12116 Prague 2, The Czech Republic f Physics Department, Brookhaven National Laboratory, Upton, Long Island, NY 11973, USA g School of Metallurgy and Materials, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK Received 28 November 1997 Abstract Hydrogenation (deuteration) of intermetallic TbNiAl with ZrNiAl type crystal structure has been studied by differential thermal analysis and X-ray and neutron powder diffraction. The compound absorbs up to 1.4 hydrogen (deuterium) atoms per formula unit at room temperature and atmospheric pressure, and desorbs hydrogen under vacuum in a multistep reaction at about 1058C, 1608C and 3208C, and deuterium at about 1908C and 4508C. Hydrogenation (deuteration) leads to an orthorhombic distortion of the hexagonal host structure; ˚ ˚ TbNiAlH : a( |c )53.7209(7); b ( |a œ3)512.353(2) A; c ( |a )57.636(1) A; TbNiAlD : a53.70187(8); b512.4011(3); 1.4 hex hex hex 1.1 ˚ c57.6075(2) A; space group Amm2. Three sorts of deuterium sites exist of which two have aluminium in their co-ordination polyhedra: trigonal bi-pyramidal [Tb Ni ] (88% occupancy) and two tetrahedral [Tb NiAl] (67% and 10% occupancy). The metal–deuterium bond 3 2 2 ˚ ˚ ˚ distances are Tb–D52.18–2.42 A, Ni–D51.50–1.90 A, and Al–D51.64–1.85 A. The deuterium–deuterium contact distances are all ˚ greater than 1.98 A.  1998 Elsevier Science S.A. All rights reserved. Keywords: Metal hydride; Hydrogen sorption; Structure refinement; Neutron diffraction 1. Introduction ing temperatures decreased strongly upon hydrogenation. In this paper we present more detailed results on the Equiatomic RENiAl compounds crystallizing with the hydrogen sorption properties of the terbium member and hexagonal ZrNiAl structure type are known for nearly all on the crystal structure of its deuteride TbNiAlD . 1.1 rare earth (RE) elements [1]. Their hydrogen sorption properties were recently studied for RE5Y, Gd, Tb, Dy, Er and Lu, with a particular emphasis on the influence of 2. Experimental details hydrogenation on the magnetic properties [2]. The com- pounds were found to absorb hydrogen at ambient tem- A sample of equiatomic composition TbNiAl was perature and atmospheric pressure to concentrations of up prepared from a mixture of elemental terbium (purity to 1.2–1.6 atoms per formula unit. Their structure under- 99.8%), nickel (99.9%) and aluminium (99.9%) by arc went an orthorhombic distortion and their magnetic order- melting in an argon atmosphere. The ingots were remelted several times to increase their homogeneity, but were not annealed. X-ray powder diffraction (Philips PW 1012 / 10 * Corresponding author. 1 and Huber Guinier diffractometers, CuKa radiation) con- Present address: National Institute of Materials and Chemical Re- search, 1-1 Higashi, Thukuba, Ibaraki 305-8565, Japan. firmed the formation of a ternary phase with hexagonal 0925-8388 / 98 / $ – see front matter  1998 Elsevier Science S.A. All rights reserved. PII: S0925-8388(97)00610-5