YbFeGe, a new structure type of equiatomic ternary germanides

Journal of Alloys and Compounds 312 (2000) 196–200

L

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YbFeGe, a new structure type of equiatomic ternary germanides a

O. Sologub , P. Salamakha

a,b,c ,

*, G. Bocelli c , S. Otani b , T. Takabatake a

a

b

Department of Quantum Matter, ADSM, Hiroshima University, Higashi-Hiroshima 739 -8526, Japan National Institute for Research in Inorganic Materials, 1 -1 Namiki, Tsukuba, Ibaraki 305 -0044, Japan c Centro per la Strutturistica Diffrattometrica CNR, Viale delle Scienze, 43100 Parma, Italy Received 19 June 2000; accepted 17 July 2000

Abstract ˚ b53.904(2) A, ˚ c56.715(3) A, ˚ The crystal structure of the new ternary germanide YbFeGe, space group C2 /m (N12), a510.607(6) A, 23 21 ˚ b 5127.58(1)8, Z54, V5220.35 A, r 59.088 g cm , m 561.67 mm was refined to R50.0313, wR2 50.0705 from single crystal X-ray diffraction data. This is the first representative of a new structure type (str. type) of intermetallic compounds. The formation and crystal ˚ b53.9034(3) A, ˚ c56.7117(4) A, ˚ structure for this compound were confirmed from X-ray powder diffraction: a510.5755(5) A, ˚ b 5127.688. An isotypic YbMnGe compound was observed: YbFeGe str. type, C2 /m space group (sp. gr.), a510.5966(4) A, ˚ ˚ b53.9014(2) A, c56.7782(3) A, b 5127.428. The crystal structures for the YbCoGe compound (TiNiSi str. type, Pnma sp. gr., ˚ b54.0392(2) A, ˚ c57.2684(4) A) ˚ and YbMn 2 Ge 2 compound (CeGa 2 Al 2 str. type, I4 /mmm sp. gr., a54.0334(5) A, ˚ a56.7168(4) A, ˚ are reported for the first time.  2000 Elsevier Science B.V. All rights reserved. c510.0334(7) A) Keywords: YbFeGe; Structure type; Equiatomic ternary germanides

1. Introduction A rich variety of structure types has been reported for the compounds of equiatomic composition containing rare earth metal, transition metal and germanium [1,2]. In most cases, structure changes take place when one transition metal is substituted for another. Among the YbMGe series, as an example, the TiNiSi type was reported for the YbNiGe and YbPtGe compounds [3,4], the CaIn 2 type was found for a copper containing germanide [5], YbPdGe crystallizes with KHg 2 type [6] and YbAgGe forms the ZrNiAl structure type [7]. The YbAuGe compound was found from X-ray powder diffraction to crystallize with LiGaGe type [8]. Merlo et al., in a recent X-ray single crystal investigation of the YbAuGe compound reported a unique a-YbAuGe structure type [9]. Dzianii et al. [10,11] claimed that the YbCoGe compound forms an unknown structure. The equiatomic compounds with manganese and iron have not been observed within the Yb–Mn–Ge and Yb–Fe–Ge systems by the same group of authors

*Corresponding author. E-mail address: [email protected] (P. Salamakha).

[10,12,13] and the formation of compounds with 9:10:10 stoichiometry and unknown structure has been reported. The present study has been pursued for the purpose of performing a phase analyses of Yb 31 – 33.3 M 34.5 – 33.3 Ge 34.5 – 33.3 samples (M5Mn,Fe,Co) and in order to establish the crystal structure of the compounds observed.

2. Experimental details Ternary samples were synthesized by arc melting of the constituent elements under a high purity argon atmosphere on a water-cooled copper hearth. In order to ensure homogeneity, the arc melted buttons were turned over and re-melted several times. Weight losses due to vaporization of ytterbium while melting were less than 2 mass% and were compensated beforehand by an extra amount of Yb. For the X-ray single crystal data collection, a single crystal was glued on the top of a glass fiber and mounted on the goniometer head. A four circle diffractometer Philips PW 1100 with graphite monochromatized MoKa ˚ was used. The least square radiation ( l50.71073 A) refinement of the 2u values of 25 strong and well centered

0925-8388 / 00 / $ – see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0925-8388( 00 )01147-6

O. Sologub et al. / Journal of Alloys and Compounds 312 (2000) 196 – 200

197

Table 1 Parameters for the single crystals X-ray data collection Compound Space group

YbFeGe C2 /m

Lattice parameters ˚ a (A) ˚ b (A) ˚ c (A) b (8)

10.607(6) 3.904(2) 6.715(3) 127.58(1)

3

˚ ) Cell volume (A Formula units per cell, Z Calculated density (g cm 23 ) Linear absorption coefficient (mm 21 ) 2umax Number of measured reflections Number of unique reflections Number of reflections with Io .4s (Io ) Number of refined parameters R, wR2 Goodness of fit ˚ 23 ) Highest / lowest residual electron density (e A

220.35 4 9.088 61.67 59.99 385 356 314 20 0.0313, 0.0705 1.017 3.2 / 22.3

reflections from the various regions of reciprocal space were used to obtain the unit-cell parameters. The data set was recorded at room temperature in a v-2u scan mode. The intensities were corrected for absorption, polarization and Lorentz effect. Further details are listed in Table 1. For the phase analyses, the X-ray powder intensities were recorded using Bruker D8 and Labo-MX diffractometers with CuKa radiation in the range from 108#2u#1208.

3. Results

3.1. X-ray single crystal refinement of the YbFeGe compound A single crystal suitable for the X-ray measurements was isolated from the surface of the alloy with composition Yb 31 Fe 34.5 Ge 34.5 . The structure was solved in the space group C2 /m by means of direct methods using SHELXS86 [14] which resulted in the positions of all atoms. The structure was refined by a full-matrix least squares program using atomic scattering factors provided by the program package SHELXL-97 [15]. The absorption cor-

Fig. 1. Perspective view of the YbFeGe structure.

rection was performed with the assistance of program DIFABS [16]. The weighting schemes included a term, which accounted for the counting statistics, and the parameter correcting for isotropic secondary extinction was optimized. The final residuals are presented in Table 1. The atomic coordinates, which correspond to their standardized form according to STIDY [17] and the thermal parameters are shown in Table 2. A perspective view of the YbFeGe structure on the XZ plane and the coordination polyhedra for the atoms are shown in Figs. 1 and 2. The coordination polyhedron for the Yb atom is formed by 18 atoms [YbYb 6 Fe 6 Ge 6 ] (Fig. 2a). The coordination number for the germanium atom is 9 and its environment is a trigonal prism with three additional atoms [GeYb 5 Fe 3 Ge] (Fig. 2c). Each iron atom is surrounded by a polyhedron formed by 11 atoms which corresponds to a deformed cubooctahedron with one ‘missing’ atom [FeYb 6 Fe 2 Ge 3 ] (Fig. 2b).

3.2. X-ray powder diffraction for the Yb9 M10 Ge10 ( M5 Mn, Fe) and YbCoGe samples X-ray phase analyses were performed for three samples using the program POWDER CELL 2.1 [18]. The lattice parameters for the compounds observed were determined using the programs TREOR90 [19], LATCON [20] and FULLPROF98 [21]. The analyses of the X-ray powder diffraction patterns of the alloys containing Mn and Fe showed the existence of

Table 2 Atomic coordinates and thermal parameters for the YbFeGe compound Atom a

Wyckoff position

x

y

z

U11 310 2 , ˚ 2) (A

U22 310 2 , ˚ 2) (A

U33 310 2 , ˚ 2) (A

U13 310 2 , ˚ 2) (A

Ueq. 310 2 , ˚ 2) (A

Yb Fe Ge

4(i) 4(i) 4(i)

0.44050(13) 0.19929(41) 0.15497(32)

0 0 0

0.22236(17) 0.59205(54) 0.19467(42)

1.97(6) 1.58(15) 1.96(12)

2.06(7) 2.04(21) 1.75(15)

2.10(6) 1.92(16) 2.13(12)

0.07(3) 0.14(12) 0.06(9)

2.04(4) 1.84(1) 1.95(6)

a

U23 5U12 50.

198

O. Sologub et al. / Journal of Alloys and Compounds 312 (2000) 196 – 200

Fig. 2. Coordination polyhedra of the atoms Yb (a), Fe (b) and Ge (c).

two phases in the case of Yb 9 Mn 10 Ge 10 (YbMnGe and YbMn 2 Ge 2 ) and three phases in the case of Yb 9 Fe 10 Ge 10 (YbFeGe, YbFe 2 Ge 2 and the traces of an unknown phase). Strong reflections selected from the X-ray pattern of the YbCoGe sample were indexed using the program TREOR90. An orthorhombic cell was suggested with parameters a56.7168(4), b54.0392(2) and c57.2684(4) ˚ The pattern simulated by using the atomic parameters of A. TiNiSi type, revealed a close similarity with the experimental one, confirming the isotypism of these two compounds. The crystallographic characteristics of the phases observed in the ternary Yb 9 M 10 Ge 10 (M5Mn, Fe) and YbCoGe samples are presented in Table 3. The crystallographic characteristics obtained for the YbFe 2 Ge 2 and YbCo 2 Ge 2 compounds agree well with the literature data [10]. The YbMn 2 Ge 2 compound was ob-

served for the first time. This result is at variance with a recent study [12] in which no formation of the YbMn 2 Ge 2 phase in the ternary Yb–Mn–Ge system at 670 K has been reported.

4. Structural relationships for the YbFeGe compound The YbFeGe structure is related to the previously studied binary OsGe 2 [22] structure and quaternary Dy 2 Fe 2 Si 2 C [23] structure (Fig. 3). All three compounds belong to a monoclinic crystal system, space group C2 /m; their atomic coordinates are presented in Table 4. The YbFeGe compound is an ordered modification of the OsGe 2 structure where the Yb atoms occupy the atomic

O. Sologub et al. / Journal of Alloys and Compounds 312 (2000) 196 – 200

199

Table 3 Phase analyses for the Yb 9 M 10 Ge 10 (M5Mn, Fe) and YbCoGe samples and crystallographic characteristics for the compounds observed Sample

Phase analysis

Yb 9 Mn 10 Ge 10

Yb 9 Fe 10 Ge 10

YbCoGe

Str. type

˚ Lattice parameters (A)

Space group

a

b

10.5966(4)

3.9014(2) b 5127.428

YbMnGe

YbFeGe

C2 /m

YbMn 2 Ge 2

CeGa 2 Al 2

I4 /mmm

YbFeGe

YbFeGe

C2 /m

YbFe 2 Ge 2

CeGa 2 Al 2

I4 /mmm

3.9282(4)

YbCoGe YbCo 2 Ge 2 (traces)

TiNiSi CeGa 2 Al 2

Pnma I4 /mmm

6.7168(4) 3.9311(5)

c

4.0334(5)

6.7782(3) 10.0334(7)

10.5755(5)

3.9034(3) b 5127.688

6.7117(4) 10.4800(8)

4.0392(2)

7.2684(4) 10.0400(7)

Fig. 3. Structural relationships between OsGe 2 , YbFeGe and Dy 2 Fe 2 Si 2 C.

sites of Ge2 and the Fe and Ge atoms substitute for the Ge1 and Os atoms, respectively. The Dy 2 Fe 2 Si 2 C structure differs from the YbFeGe one by the presence of carbon atoms in the site 2(a) 0,0,0. Similarly to the previously investigated CeFeGe structure that forms a PbFCl type [24], the YbFeGe structure can be considered as an intergrowth of CeGa 2 Al 2 - and W-type segments. Structurally related to YbFeGe type is also the UFeGe type (P2 1 /m space group) [25] that is a monoclinic modification of the TiNiSi structure type. The coordination polyhedra for the Fe atoms in the YbFeGe

structure correspond to the Fe1 and Ge2 polyhedra in the UFeGe structure while the Ge atoms in the YbFeGe compound have coordination polyhedra similar to that for Fe2 and Ge1 atoms in the UFeGe structure.

Acknowledgements One of the authors (O. Sologub) wishes to thank JSPS for a 2-year fellowship in Japan.

Table 4 Atomic coordinates in the OsGe 2 , YbFeGe and Dy 2 Fe 2 Si 2 C structures a OsGe 2

YbFeGe

Dy 2 Fe 2 Si 2 C

Atom

x

z

Atom

x

z

Atom

x

z

Os Ge 1 Ge 2

0.154 0.143 0.399

0.200 0.530 0.112

Ge Fe Yb

0.15497 0.19929 0.44050

0.19467 0.59205 0.22236

Fe Si Dy C

0.2030 0.1562 0.4389 0

0.3091 0.6050 0.1714 0

a

y50 for all atoms.

200

O. Sologub et al. / Journal of Alloys and Compounds 312 (2000) 196 – 200

References [1] P.S. Salamakha, O.L. Sologub, O.I. Bodak, in: K. Gschneidner, L. Eyring (Eds.), Handbook on Physics and Chemistry of Rare Earths, Elsevier Science B.V., The Netherlands, Vol. 27, 1999, p. 1, Chapter 173. [2] P.S. Salamakha, in: K. Gschneidner, L. Eyring (Eds.), Handbook on Physics and Chemistry of Rare Earths, Elsevier Science B.V., The Netherlands, Vol. 27, 1999, p. 225, Chapter 174. [3] Yu.K. Gorelenko, P.K. Starodub, V.A. Bruskov, R.V. Skolozdra, V.I. Yarovetz, O.I. Bodak, V.K. Pecharsky, Ukr. Fiz. Zh. 29 (1984) 867. [4] O.L. Borisenko, Ph.D. Chemistry Thesis, Moscow State University, Moscow, 1993. [5] A. Iandelli, J. Alloys Comp. 198 (1993) 141. [6] Yu.D. Seropegin, O.L. Borisenko, O.I. Bodak, V.N. Nikiforov, M.V. Kovachikova, Yu.V. Kochetkov, J. Alloys Comp. 216 (1994) 259. [7] B. Gibson, R. Pottgen, R.K. Kremer, A. Simon, K. Ziebeck, J. Alloys Comp. 239 (1996) 34. [8] D. Rossi, R. Marazza, R. Ferro, J. Alloys Comp. 187 (1992) 267. [9] F. Merlo, M. Pani, F. Canepa, M.L. Fornasini, J. Alloys Comp. 264 (1998) 82. [10] R.B. Dzianii, Ph.D. Chemistry Thesis, L’viv State University, L’viv, 1995. [11] R.B. Dzianii, O.I. Bodak, V.V. Pavlyuk, Neorgan. Mater. 31 (7) (1995) 985. [12] R.B. Dzianii, O.I. Bodak, V.V. Pavlyuk, I.M. Potereiko, Phase equilibria in the Yb–Mn–Si(Ge) systems at 670 K, Ukr. TNTB 11.05.95, 1188 (1995) 95.

[13] R.B. Dzianii, O.I. Bodak, V.V. Pavlyuk, Metally 2 (1995) 173. [14] G.M. Sheldrick, SHELXS-86, Program for Crystal Structure De¨ termination, University of Gottingen, Germany, 1986. [15] G.M. Sheldrick, SHELXS-97, Program for Crystal Structure Refine¨ ment, University of Gottingen, Germany, 1997. [16] N. Walker, O. Stewart, Acta Crystallogr. A39 (1983) 158. ´ L. Gelato, B. Chabot, M. Penzo, K. Cenzual, R. [17] E. Parthe, Gladyshevskii, TYPIX. Standardized data and crystal chemical characterization of inorganic structure types, in: 8th Edition, Gmelin Handbook of Inorganic and Organometallic Chemistry, Vol. 1, Springer-Verlag, Berlin, 1993. [18] G. Nolze, W. Kraus, PowderCell 2.1 Program, BAM, Berlin, Germany, 1999. [19] P.E. Werner, TREOR90, Program for Trail and Error Indexing of Powder Patterns, University of Stockholm, Stockholm, Sweden, 1990. [20] D. Schwarzenbach, Program LATCON, UNI Lausanne, Switzerland, 1975. [21] J. Rodriguez-Carvajal, FULLPROF, Laboratoire Leon Brillouin (CEA-CNRS), France, 1998. [22] G. Weitz, L. Born, E. Hellner, Z. Metallkunde 51 (4) (1960) 238. [23] L. Paccard, D. Paccard, J. Less-Common Metals 137 (1988) 297. ´ B. Chabot, in: K. Gschneidner, L. Eyring (Eds.), [24] E. Parthe, Handbook on the Physics and Chemistry of Rare Earths, Elsevier Science B.V., The Netherlands, Vol. 6, 1984, p. 113, Chapter 48. [25] F. Canepa, P. Manfrinetti, M. Pani, A. Palenzona, J. Alloys Comp. 234 (1996) 225.