BHoNi4, hexagonal, P6/mmm (No. 191), a = 4.9696(4) Å, c = 6.9419(5) Å, V= 148.5 Å3, Z= 2, ρm = 9.13(1) g·cm-3, R(P) = 0.072, wR(P) = 0.099, R(I) = 0.065, T= 300 K

Belger, A.

Geupel, S.

Graw, G.

Paufler, P.

English

Repositorium für Naturwissenschaften und Technik

Z. Kristallogr. NCS 215 (2000) 4 8 1 ^ 8 2 481 © by Oldenbourg Wissenschaftsverlag, München Refinement of the crystal structure of holmium tetranickel boride, HoNi4B S. Geupel*1, ', A. Belger1, P. Paufler1 and G. Graw11 I Technische Universität Dresden, Institut für Kristallographie und Festkörperphysik, D-01062 Dresden, Germany II Institut für Festkörper- und Werkstofforschung Dresden, Postfach 270016, D-01171 Dresden, Germany Received May 22, 2000, CSD-No. 409500 Abstract BHoNi4, hexagonal, P6/mmm (No. 191), a = 4.9696(4) A , c = 6.9419(5) A , V= 148.5 A 3 , Z = 2, pm = 9.13(1) g-cm"3, R(P) = 0.072, wR(P) = 0.099, R(I) = 0.065, T= 300 K. Source of material A polycrystalline rod with nominal composition HoNi4B was prepared from holmium pieces, nickel powder and boron powder. A stoichiometric mixture of the high-purity elements was pressed to pellets, which have been arc-melted under argon atmosphere on a water-cooled copper heart. Melting of the buttons has been repeated three times in order to improve the sample homogeneity. The melt was cast into a rod-shaped copper mould. A special annealing treatment (duration 75 h, temperature up to 1370 K) was performed within a resistance furnace under argon atmosphere. The composition of the annealed sample was determined with electron probe microanalysis applying the WDX mode. Experimental details Accurate lattice parameters of HoNi4B were measured at temperatures between 300 K and 25 K using a SIEMENS D5000 powder diffractometer equipped with a low-temperature chamber (Fa. Anton Paar). Initial values for the refinement of lattice parameters and atomic coordinates were taken from CaNi4B [2], Correction of systematic errors of measured peak positions was done by means of refinement parameters displacement and transparency. Refinement of individual isotropic temperature factors failed because of unreasonable parameter shifts. Therefore, an overall temperature factor was refined only. Discussion The title compound is isotypic with YNi4B [ 1 ] and CaNi4B [2]. It was previously studied with powder diffraction, but only lattice parameters were reported [3]. Here we present the first structure refinement of HoNi4B using X-ray powder diffraction data. HoNi4B (P6/mmm - idcba) crystallizes with the CeCo4B structure type [4]. Perpendicular to the c axis, two layers of CaCus-type and CeCo3B2-type are alternately stacked. Parallel to the c axis, the Ho atoms form linear chains which are located at channels with hexagonal cross-section (Hoi—Ho2 distance 3.471 A ) . Each Hoi atom is coordinated by 6 Ni2 atoms at 2.862 A and 12 Ni 1 at-oms at 3.202 A , whereas each Ho2 atom is surrounded by 6 B at-oms at 2.862 A and 12 Ni 1 atoms at 2.878 A . The B atoms occupy the centres of trigonal prisms formed by 6 Nil atoms (Nil—B distance 2.041 A ) . Atomic coordinates correspond to the stan-dardized form according to STRUCTURE TIDY [5]. The linear thermal expansion at temperatures between 300 K and 25 K indi-cates a nearly isotropic behaviour: a a = 1.3 x 10" 10"5 KT1 Table 1. Data collection and handling. 5 KT1, a c = 1.0 x Powder: grey Wavelength: Cu Ka radiation ( 1.54439 A) M: 711.0 cm-1 Diffractometer: SIEMENS D5000 Scan mode: Step scan 26max, stepwidth: 120°, 0.01 N(points )measured: 10501 WftWjmeasured: 68 N(param) refined: 17 Programs: WYRIET [6], SCHAKAL92 [7] Table 2. Atomic coordinates and displacement parameters (in A 2). Atom Site x y z c/iso Ni(l) 6/ 1/2 0 0.2091(1) 0.0082(3) Ni(2) 2d 1/3 2/3 1/2 0.0082 B 2c 1/3 2/3 0 0.0082 Ho(l) lb 0 0 1/2 0.0082 Ho(2) 1 a 0 0 0 0.0082 * Correspondence author (e-mail: sandra.geupel@uni-bayreuth.de) ' current address: Universität Bayreuth, Lehrstuhl für Kristallographie, D-95440 Bayreuth, Germany 482 H o l m i u m nickel b o n d e (1:4:1) Acknowledgment. Support by the Deutsche Forschungsgemeinschaft is grate-fully acknowledged. References 1. Niihara, K.; Katayama, Y.; Yajima, S.: The YNi4B compound in yttrium-nickel-boron system. Chem. Lett. (1973) 613-614. 2. Jung, W.; Weltzer, M.: Die ternären Calcium-Nickelboride CaNiiB, Ca3Ni7B2,Ca5Nii5B4undCaNii2B6.Z. Kristallogr. 196(1991) 169-178. 3. Chernyak, G. V.; Chaban, N. F.; Kuz'ma, Yu. B.: New borides of the rare earth metals and nickel. Inorg. Mater. 18 (1982) 590-592. 4. Kuz'ma, Yu. B.; Bilonizhko, N. S.: New boride structural types in the ho-mologous series based on the CaCus and CeCo3B2 types. Sov. Phys. Crystallogr. 18 (1974) 447-449. 5. Gelato, L. M.; Parthd, E.: STRUCTURE TIDY - a computer program to standardize crystal structure data. J. Appl. Crystallogr. 20 (1987) 139-143. 6. Schneider, J.: WYRIET, powder profile refinement and structure analysis package for personal computers, version 3. University of Miinchen, Ger-many 1995. 7. Keller, E.: SCHAKAL92, computer program for the graphic representa-tion of molecular and crystallographic models. University of Freiburg, Germany 1992. 

Refinement of the crystal structure of holmium tetranickel boride, HoNi4B

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Refinement of the crystal structure of holmium tetranickel boride, HoNi4B

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