L Journal of Alloys and Compounds 356–357 (2003) 142–146 www.elsevier.com / locate / jallcom Crystallographic and magnetic structure of Pr Fe AuD 6 13 13 a b b, c a a * V.A. Yartys , F.R. de Boer , K.H.J. Buschow , B. Ouladdiaf , H.W. Brinks , B.C. Hauback a Institute for Energy Technology, P .O. Box 40, Kjeller, N 2027, Norway b Van der Waals-Zeeman Institute, University of Amsterdam Valckenierstr. 65, 1018 XE Amsterdam, The Netherlands c Institute Laue-Langevin, B.P . 156, 38042 Grenoble Cedex 9, France Received 1 June 2002; accepted 25 October 2002 Abstract Neutron diffraction performed on deuterated powder samples of Pr Fe Au shows that the crystal structure of the parent compound is 6 13 retained upon charging with deuterium. The refined composition of the deuteride is Pr Fe AuD . The deuterium atoms occupy various 6 13 13 types of interstitial sites bounded by Pr and Fe atoms. Each of these sites is surrounded by at least two Pr atoms. A collinear antiferromagnetic ordering of the four Fe and the two Pr sublattices was reported previously for the uncharged Pr Fe Au compound. By 6 13 contrast, a collinear ferromagnetic structure has been derived from the present neutron data of the deuteride. The easy moment direction is the same in Pr Fe AuD and Pr Fe Au, being perpendicular to the c-axis. For the deuteride this result was derived from a 6 13 13 6 13 complementary synchrotron radiation X-ray study made on magnetically aligned particles of the ferromagnetic deuteride.  2002 Elsevier B.V. All rights reserved. Keywords: Hydrogen storage materials; Gas–solid reactions; Neutron diffraction; X-ray synchrotron diffraction; Crystal structure and symmetry 1. Introduction generally smaller than their free-ion values while the average Fe ordered value is 2.2 m / Fe, in agreement with B ¨ Rare earth compounds of the type R Fe X (X5Cu, Ag, Mossbauer results. 6 13 Au, Si, Sn, etc.) form only for the first few members of the The R Fe X compounds easily absorb fairly large 6 13 rare earth series. They crystallise in the tetragonal amounts of hydrogen leading to drastic changes of their Nd Fe Si-type structure (space group I4 / mcm) [1,2]. This magnetic properties [4,9]. In the present investigation we 6 13 structure is an ordered variant of the La Co Ga structure have charged the Pr Fe Au compound with deuterium for 6 11 3 6 13 [3] with two rare earth sites R1 (16l ) and R2 (8f ) and four neutron diffraction experiments. The purpose of our in- Fe sites Fe1 (16l ), Fe2 (16k), Fe3 ( 16l ) and Fe4 (4d ). vestigation is to determine the crystallographic location of 1 2 Magnetic measurements have shown that the magnetic the D atoms and to determine the magnetic structure of the ordering of these compounds is antiferromagnetic (AF) deuteride. ´ with fairly high Neel temperatures, typically around 400 K ¨ [4,5], also confirmed by Mossbauer spectroscopy [6–8]. Neutron diffraction performed on powder samples of 2. Experimental several of these compounds revealed a collinear AF ordering of the four Fe and two R sublattices associated The Pr Fe Au sample was prepared by arc melting 6 13 with the wave vector q5(001) [5]. The moments of all starting materials of at least 99.9% purity, using an excess sublattices located at ( xy0) layers, sandwiched between of about 2% of Pr. After annealing for about 3 weeks at successive X layers perpendicular to c at z 20.25 and 0.25 1070 K, the sample was quenched to room temperature. are confined to the same direction within the ( xy0) plane. X-ray diffraction diagrams showed that the sample was They revert their direction collectively when going to the approximately single phase (Nd Fe Si type structure). 6 13 next X layers at z50.25, 0.75. The R moments at 1.5 K are The synthesis of the deuteride was performed at deuterium pressures not exceeding 2 bar using deuterium gas with a purity of 99.8%. The starting alloy was initially *Corresponding author. Tel.: 131-20-525-5714; fax: 131-20-525- activated by annealing in a dynamic vacuum at 600 K for 5788. E-mail address: buschow@science.uva.nl (K.H.J. Buschow). 30 min. After activation, the sample was cooled to room 0925-8388 / 02 / $ – see front matter  2002 Elsevier B.V. All rights reserved. doi:10.1016/S0925-8388(02)01222-7