L Journal of Alloys and Compounds 339 (2002) 30–34 www.elsevier.com / locate / jallcom 57 ¨ X-ray powder diffraction and Fe Mossbauer spectroscopy study on Fe NbS 0.47 2 1 * L. Ehm , S. Vogel , K. Knorr, P. Schmid-Beurmann,W. Depmeier ¨ ¨ Institut f ur Geowissenschaften, Universitat Kiel, Olshausenstr. 40, 24098 Kiel, Germany Received 9 November 2001; accepted 19 November 2001 Abstract The crystal structure of Fe NbS was refined using X-ray powder diffraction. Fe NbS crystallises in the space group P6 22 with 0.47 2 0.47 2 3 ˚ ˚ the unit cell parameters a 55.7905(2) A and c 512.3891(2) A. The NbS sublattice of Fe NbS is similar to 2H–NbS . The niobium 2 0.47 2 2 atoms are coordinated trigonal prismatically by sulfur atoms. Sandwiches of NbS are stacked onto each other along the c direction, 2 separated by van-der-Waals gaps. The iron atoms are located inside the van-der-Waals gaps on three symmetrically nonequivalent ¨ positions. The distribution over these three positions is not uniform. The valence state of the iron atoms was investigated by Mossbauer ¨ spectroscopy. The Mossbauer spectroscopy shows that the iron is predominantly ferric and high spin, but a minor part is low spin.  2002 Elsevier Science B.V. All rights reserved. ¨ Keywords: Semiconductors; Crystal structure; X-ray diffraction; Mossbauer spectroscopy PACS: 61.66; 71.22.T; 61.10; 76.80; 75.50.P 1. Introduction several authors [4–7]. The NbS sub-lattice in Fe NbS is 2 x 2 similar to that of 2H–NbS [8]. Layers of NbS 2 2 The layered transition-metal dichalcogenides have been sandwiches, with niobium coordinated trigonal prismatical- extensively investigated experimentally and theoretically in ly by six sulphur atoms, are stacked onto each other along recent years. Due to their potential technological applica- the c direction. The intra-layer bonding is mainly covalent, tions in the catalysis of petrochemical processes [1] or as whereas the inter-layer bonding is dominated by van-der- cathodes in solid state batteries [2,3], there is considerable Waals forces. Fe NbS crystallises in space group P6 22 x 2 3 interest in understanding the structure and properties of with the niobium atoms on the Wyckoff positions 2 a and their intercalation compounds. Although Fe NbS has not 4f, and the sulfur atoms on the Wyckoff position 12 i. The x 2 been proven rigorously to undergo typical intercalation or iron atoms can occupy the three Wyckoff positions 2 b, 2 c deintercalation reactions near room temperature, it can and 2 d, all of which have site symmetry 3.2 and are serve as a model structure for intercalation compounds located in the van-der-Waals gaps. These sites are coordi- A NbS , where A represents an interchangeable chemical nated by six sulphur atoms forming a slightly distorted x 2 species. octahedron. Here we present results of a structure refine- 57 The structure and the physical properties of Fe NbS , ment against X-ray powder diffraction data and Fe x 2 ¨ e.g. the resistivity, the Hall coefficients, the magnetic Mossbauer spectroscopy of Fe NbS . 0.47 2 susceptibility and the Curie temperature, are strongly dependent on the iron content x. For x ¯ 1/4 and x ¯ 1/3, the structures and the physical properties were studied by 2. Experimental Samples of Fe NbS with x ¯ 1/2 were prepared by x 2 *Corresponding author. LANL, MS H805, P.O. Box 1663, Los sintering a stoichiometric mixture of the elements in an Alamos, NM 87545, USA. evacuated silica ampoule at 1175 K. After a reaction time E-mail address: ehm@min.uni-kiel.de (L. Ehm). 1 of 3 days the sample was gradually cooled to room Present address: LANL, MS H805, P.O. Box 1663, Los Alamos, NM 87545, USA. temperature by decreasing the temperature by 100 K every 0925-8388 / 02 / $ – see front matter  2002 Elsevier Science B.V. All rights reserved. PII: S0925-8388(01)01980-6