Refinement of the crystal structure of NdGe2Ni2

L

Journal of Alloys and Compounds 278 (1998) L6–L7

Letter

Refinement of the crystal structure of NdGe 2 Ni 2 Lingmin Zeng, Hugo F. Franzen* Ames Laboratory-DOE, Iowa State University, Ames, Iowa 50011, USA Received 27 January 1998

Abstract The structure of NdGe 2 Ni 2 was refined using single-crystal X-ray data. The refinement shows the crystal structure of NdGe 2 Ni 2 is ˚ c59.841(2) A, ˚ V5167.3(2) A ˚ 3 and tetragonal with the Al 4 Ba-type structure with the space group I4 / mmm (No. 139), a54.123(4) A, Z52 at room temperature.  1998 Elsevier Science S.A. All rights reserved. Keywords: Neodymium; Nickel; Germanium; Crystal structure

1. Introduction In previous work the RGe 2 Ni 2 (R5rare earth) compounds: CeGe 2 Ni 2 [1], PrGe 2 Ni 2 [2], TbGe 2 Ni 2 [3], HoGe 2 Ni 2 [3] were investigated. Some unusual magnetic properties were found [3]. Magnetic susceptibility and neutron diffraction investigation on NdGe 2 Ni 2 [4] was also reported. Because the structure study of NdGe 2 Ni 2 was based on powder diffraction data we report the results of refinement of the crystal structure using single-crystal X-ray data.

2. Experimental details A sample with nominal composition ‘Nd 2 Ge 5 Ni 3 ’ was prepared by arc melting under an Argon atmosphere using the elements: neodymium (Ames Lab. 99.6%), germanium (Alfa, 2100 mesh, 99.999%), nickel (Fisher, purified powder). Before melting, a mixture of Ge and Ni powder was pelletized under a pressure of 10 000 psi. The arc melted sample was encased in Ta foil and sealed in an evacuated quartz tube and then annealed at 7508C for 3 weeks in a resistance furnace. The sample was cooled to 238C at a rate of 108C h 21 . A metallic single crystal of NdGe 2 Ni 2 with dimensions of 0.08 mm30.12 mm30.21 mm was selected from the Nd 2 Ge 5 Ni 3 sample for structure determination. The crystal

quality was checked with a Weissenberg camera. The data collection was performed with a four-circle diffractometer having a rotating anode (Rigaku FC6R), using monochromated Mo Ka radiation and the v 22u scan technique. The crystal structure was solved using direct methods with the SHELXS program [5] and was refined using the fullmatrix, least-squares techniques with TEXSAN software [6]. Details of the structure analysis are listed in Table 1. Table 1 Crystal data, data collection and refinement parameters for NdGe 2 Ni 2 Formula Formula weight Crystal system Space group Cell dimensions ˚ a (A) ˚ c (A) ˚ 3) V (A Z d (calc.) (g cm 23 ) Crystal size (mm) Temperature (K) Diffractometer Radiation (monochr. in incident beam) Scan mode Index range (h, k, l) No. of data collection: No. of reflections No. of variables Ra Rv b Goodness of fit c a

0925-8388 / 98 / $19.00  1998 Elsevier Science S.A. All rights reserved. PII: S0925-8388( 98 )00523-4

4.123(4) 9.841(4) 167.3(2) 2 8.076 0.0830.1230.21 296 Rigaku AFC6R ˚ Mo Ka (0.71069 A) 2u 2v 0#h#6, 26#k#6, 214#l#14 793 126 8 0.047 0.042 1.204

R5S Fo 2 Fc / S Fo . Rv 5[Sw( Fo 2 Fc )2 / Sw Fo 2 ] 1 / 2 ; w51 /s 2 ( Fo ). c GOF5S[( Fo 2 Fc ) /si ] /(Nobs 2Nparameters ). b

*Corresponding author. Fax: 11 515 2945718.

NdGe 2 Ni 2 406.84 tetragonal I4 / mmm (no. 139)

L. Zeng, H.F. Franzen / Journal of Alloys and Compounds 278 (1998) L6 –L7

L7

Table 3 ˚ below 3.7 for NdGe 2 Ni 2 Interatomic distances (A) Nd–Ge Nd–Ge Nd–Ni Ge–Nd Ge–Nd Ge–Ge Ge–Ni Ni–Nd Ni–Ge Ni–Ni

3.639(2) 3.185(2) 3.210(1) 3.639(2) 3.185(2) 2.563(2) 2.375(2) 3.210(1) 2.375(2) 2.915(3)

23 83 83 13 43 13 43 43 43 43

Al 4 Ba-type structure (Fig. 1), in agreement with the results based on powder diffraction data [2,4]. The refined positional and thermal parameters for NdGe 2 Ni 2 are given in Table 2. Table 3 lists the interatomic distances below 3.7 ˚ for NdGe 2 Ni 2 . A

Acknowledgements This research was supported by the Office of the Basic Energy Sciences, Materials Sciences Division, U.S. Department of Energy. The Ames Laboratory is operated for DOE by Iowa State University under contract No. W-7405Eng-82. Fig. 1. Projection of the structure of NdGe 2 Ni 2 along [010] (large circles, Nd; medium circles, Ge; small circles, Ni).

3. Results and discussion The cell parameters were refined on the basis of 25 ˚ and centered reflections to a54.123(4), c59.841(4) A 3 ˚ V5167.3(2) A . The Laue class was determined to be 4 / mmm, the lattice type was I. According to the systematic extinctions (hkl: h1k1l52n, hk0: h1k52n, 0kl: k1l52n, hhl: l12n, h00: h52n, and 00l: l52n), we chose the space group I / 4mmm. The final refinements with anisotropic displacement parameters converged at R5 0.047, R w 50.042 and GOF51.204. These results confirmed that the crystal structure of NdGe 2 Ni 2 is tetragonal,

References [1] O.I. Bodak, E.I. Gladyshevskii, P.I. Kripyakevich, Inorganic Materials, Translated from Iizvestiya Akademii hauk Sssr, Neorganicheskie Materialy, 2(12) (1966) 1861. ~ Monatshefte Fuer Chemie 100 (1969) 444. [2] W. Rieger, E. Parthe, [3] H. Pinto, M. Mclanmud, M. Kuznietz, H. Shaked, Phys. Rev. B 31 (1985) 508. ´ Y. Allain, G. Andre, ~ J. Magn. Magn. Mater. 75 [4] A. Szytula, A. Oles, (1988) 298. [5] G.M. Sheldrick, SHELXS-86, Programs for Structure Determina¨ Gottingen, ¨ tion, Universitat Germany, 1986. [6] TEXSAN: Single-crystal Structure Analysis Software, Version 5.0; Molecular Structure Corp., The Woodlands, TX, 1989.

Table 2 Atomic positional and thermal parameters for NdGe 2 Ni 2 atom

Wyckoff position

x

y

z

occ.

Beq /A2

U11 5U22

U33

U12

U13

U23

Nd Ge Ni

2a 4e 4d

0 0

0 0 0

0 0.3698(1)

1.0 1.0 1.0

0.67(2) 0.88(3) 0.96(3)

0.0094(3) 0.0123(4) 0.0151(4)

0.0065(6) 0.0087(8) 0.0062(7)

0 0 0

0 0 0

0 0 0

1 ] 2

1 ] 4