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Ternary system Tm–Cu–Ge: isothermal section of the phase diagram at 870 K and crystal structures of the compounds
Journal of Alloys and Compounds 367 (2004) 70–75
Ternary system Tm–Cu–Ge: isothermal section of the phase diagram at 870 K and crystal structures of the compounds L.O. Fedyna a , O.I. Bodak a,∗ , Ya.O. Tokaychuk a,1 , M.F. Fedyna b , I.R. Mokra a a
Department of Inorganic Chemistry, Ivan Franko National University of L’viv, Kyryla i Mefodiya str. 6, UA-79005 L’viv, Ukraine b Ukrainian State University of Forest and Wood Technology, Chuprynky str. 105, UA-79057 L’viv, Ukraine
Abstract The isothermal section of the Tm–Cu–Ge phase diagram at 870 K was constructed using X-ray phase analysis. The existence of three ternary compounds was confirmed: TmCu2 Ge2 (structure type CeAl2 Ga2 , space group I4/mmm, Pearson code tI10, a = 3.99155(8) Å, c = 10.3285(2) Å), Tm2 CuGe6 (structure type Ce2 CuGe6 , space group Amm2, Pearson code oS18, a = 4.061(1) Å, b = 3.957(4) Å, c = 20.76(2) Å) and Tm6 Cu8 Ge8 (structure type Gd6 Cu8 Ge8 , space group Immm, Pearson code oI22, a = 13.7407(3) Å, b = 6.5995(1) Å, c = 4.1368(1) Å). A new ternary copper germanide TmCu1.24 Ge0.76 (structure type CaIn2 , space group P63 /mmc, Pearson code hP6, a = 4.42254(8) Å, c = 7.0477(2) Å) was found. The crystal structures of TmCu2 Ge2 , Tm6 Cu8 Ge8 and TmCu1.24 Ge0.76 were refined by full-profile Rietveld method using X-ray powder diffraction data. The binary compound Tm0.9 Ge2 (structure type ZrSi2 ) dissolves up to 5 at.% of Cu. The lattice parameters refined for the sample Tm31 Cu5 Ge64 (a = 4.042(1) Å, b = 15.793(4) Å, c = 3.906(2) Å) slightly increased, compared with Tm0.9 Ge2 . The solubility of the third component in the other binary phases was found to be negligible. © 2003 Elsevier B.V. All rights reserved. Keywords: Tm–Cu–Ge; Phase diagram; Isothermal section; Intermetallic compounds; Crystal structure
1. Introduction The binary systems at the boundaries of the Tm–Cu–Ge ternary system have been widely studied and the phase diagrams over the whole concentration regions have been constructed. So, according to [1], five binary compounds form in the Tm–Cu system. The phase diagram of the Tm–Ge system was constructed by Eremenko et al. [2] and eight binary phases have been reported. Recently, Venturini et al. [3] reinvestigated the crystal structure of the non-stoichiometric AlB2 -type compound and reported some new binary TmGe2−x phases, derived from the AlB2 type. The crystal structures of three new TmGe2−x compounds were reported in [4]. According to [5], four intermediate phases exist in the Cu–Ge binary system. Crystallographic data of the binary compounds obtained in these systems are listed in Table 1. The interaction of thulium with copper and germanium has not yet been studied systematically over the ∗
Corresponding author. Tel.: +38-322-742-388. E-mail address: [email protected] (O.I. Bodak). 1 Present address: Laboratoire de Cristallographie, Universit´ e de Gen`eve, quai Ernest-Ansermet 24, CH-1211 Gen`eve, Switzerland. 0925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2003.08.014
whole concentration range. The existence of ternary compounds, crystallizing with well-known structure types, such as TmCu2 Ge2 (CeAl2 Ga2 type) [18], Tm2 CuGe6 (Ce2 CuGe6 type) [19], Tm6 Cu8 Ge8 (Gd6 Cu8 Ge8 type) [20], TmCu1–0.67 Ge1–1.33 (AlB2 type) [21], TmCuGe (CaIn2 type) [22] and Tm5 CuGe10 (CeNiSi2 type) [23], have been reported. These compounds were synthesized using different techniques and different conditions; no atomic parameters were refined, except for TmCuGe, crystallizing in the AlB2 structure type [21]. The present study was carried out to construct the isothermal section of the phase diagram of the Tm–Cu–Ge system at 870 K, to obtain ternary compounds and determine their crystal structures.
2. Experimental Samples for investigation with the total weight 1 g were prepared from pieces of pure metals (thulium, 99.82 wt.%; copper, 99.90 wt.%; germanium, 99.99 wt.%) by arc melting under purified argon atmosphere under a pressure of 1.1×105 Pa (with Ti as a getter). To ensure homogeneity, the samples were remelted twice. During the sample preparation
L.O. Fedyna et al. / Journal of Alloys and Compounds 367 (2004) 70–75
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Table 1 Crystallographic data of the binary compounds in the Tm–Cu, Tm–Ge and Cu–Ge systems Compound
Structure type
Space group
TmCu5 Tm2 Cu9 a Tm2 Cu7 a TmCu2 TmCu Tm2 Ge5 a Tm0.9 Ge2 TmGe1.9 a TmGe1.83 a -TmGe2−x a ␣-TmGe2−x a Tm2 Ge3 Tm2 Ge3 a Tm3 Ge4 TmGe Tm11 Ge10 Tm5 Ge4 Tm5 Ge3 Cu5 Ge2 a Cu3 Gea Cu3 Gea
AuBe5 – – KHg2 CsCl Er2 Ge5 ZrSi2 own ErGe1.83 Monoclinicb Monoclinicb AlB2 own Er3 Ge4 CrB Ho11 Ge10 Sm5 Ge4 Mn5 Si3 BiF3 Na3 As Cu3 Ti
F 4¯ 3m – – Imma ¯ Pm3m Pmmn Cmcm Pmma Cmcm
cF23 – – oI12 cP2 oP14 oS12 oP20 oS24
P6/mmm C2/c Cmcm Cmcm I4/mmm Pnma P63 /mcm ¯ Fm3m P63 /mmc Pmmn
hP3 mS20 oS28 oS8 tI84 oP36 hP16 cF16 hP8 oP8
Cu3 Ge
–
P21 /∗
–
2.626 2.633(2)
Cu17 Ge3 a
Mg
P63 /mmc
hP2
2.5923
a b
Pearson code
Cell parameters a (Å)
b (Å)
c (Å)
6.991 – – 4.266 3.415 4.000 4.004 3.879 4.050 3.902 3.8778 3.88 9.0577 3.980 4.185 10.72 7.49 8.31 5.906 4.169 5.28
– – – 6.697 – 3.875 15.713 4.034 29.460 6.705 6.632 – 7.7596 10.490 10.524 – 14.36 – – – 4.22
– – – 7.247 – 18.103 3.864 22.544 3.887 4.075 4.078 4.07 6.6386 14.049 3.885 16.01 7.54 6.23 – 7.499 4.54
4.192 4.203(1) –
4.559 4.553(3) 4.2247
β (◦ )
Reference
– – – – – – – – – 89.79 89.83 – 115.678 – – – – – – – –
[6] [1] [1] [7] [8] [4] [4] [4] [4] [3] [3] [9] [3] [10] [2] [11] [12] [13] [14] [14] [15]
89.41 89.63(8) –
[16] Present work [17]
Compound not observed at 870 K. Monoclinic deformed AlB2 -type structure with ordered Ge vacancies.
the weight losses were less than 1% of the total mass. All samples were annealed in quartz ampoules under vacuum at 870 ± 10 K for 740 h and quenched in cold water. The phase analysis was carried out using X-ray powder diffraction: Debye–Scherrer technique (cameras RKD-57.3, non-filtered Cr K␣ radiation) and DRON-2 powder diffractometer (Fe K␣ radiation). The crystal structures of the ternary compounds were refined from X-ray powder diffraction data, obtained on a DRON-3M diffractometer (Cu K␣ radiation, step scan mode). All procedures, including indexing, refinement of the lattice and atomic parameters and calculations of the interatomic distances, were performed with the CSD [24] and FullProf [25] program packages.
3. Results and discussion Using X-ray phase analysis we have confirmed the existence of 10 intermediate phases in the boundary binary systems at 870 K: Tm0.9 Ge2 (ZrSi2 type), TmGe1.5 (AlB2 type, or a derivative of this type), Tm3 Ge4 (Er3 Ge4 type), Tm11 Ge10 (Ho11 Ge10 type), Tm5 Ge4 (Sm5 Ge4 type), Tm5 Ge3 (Mn5 Si3 type), TmCu5 (AuBe5 type), TmCu2 (KHg2 type), TmCu (CsCl type) and Cu3 Ge. Using profile fitting, the powder pattern of the Cu3 Ge compound was indexed in monoclinic symmetry with lattice constants a = 2.633(2) Å, b = 4.203(1) Å, c = 4.553(3) Å,
β = 89.63(8)◦ , which are in good agreement with literature data [16]. The isothermal section of the phase diagram of the Tm–Cu–Ge ternary system at 870 K is shown in Fig. 1. It was constructed by means of X-ray phase and structural analysis of 90 ternary alloys. The binary germanide Tm0.9 Ge2 dissolves up to 5 at.% Cu. The lattice parameters, refined from X-ray powder data of the sample Tm31 Cu5 Ge64 (a = 4.042(1) Å, b = 15.793(4) Å, c = 3.906(2) Å), slightly increased, compared with Tm0.9 Ge2 (a = 4.004 Å, b = 15.713 Å, c = 3.864 Å) [4]. The other binary compounds do not show appreciable ranges of solubility. The existence of three ternary compounds, TmCu2 Ge2 , Tm2 CuGe6 and Tm6 Cu8 Ge8 , was confirmed in the Tm–Cu–Ge system at 870 K. The formation of these phases at the stoichiometric compositions is in good agreement with literature data. The new ternary compound TmCu1.24 Ge0.76 was obtained in the investigated system at 870 K. The 2θ values and intensities of the reflections in the powder diffraction pattern of the sample Tm34 Cu41 Ge25 indicated that this compound could be isostructural with CaIn2 (space group P63 /mmc). The crystal structures of TmCu2 Ge2 , Tm6 Cu8 Ge8 and TmCu1.24 Ge0.76 were refined by a full-profile Rietveld method using X-ray powder diffraction data. The observed and calculated powder diffraction patterns with difference plots are shown in Fig. 2. The corresponding lattice parameters and R-factors are
72
L.O. Fedyna et al. / Journal of Alloys and Compounds 367 (2004) 70–75
870 K
1. TmCu2Ge2 2. Tm2CuGe6 3. Tm6Cu8Ge8 4. TmCu1.24Ge0.76
Tm0.9Ge2 TmGe1.5 Tm3Ge4 Tm11Ge10 Tm5Ge4 Tm5Ge3 Cu3Ge
TmCu5
TmCu2
TmCu
Fig. 1. Isothermal section of the phase diagram of the Tm–Cu–Ge ternary system at 870 K.
Table 2 Crystallographic data of the ternary compounds in the Tm–Cu–Ge system No.a
Compound
1 2 3 4
TmCu2 Ge2 Tm2 CuGe6 Tm6 Cu8 Ge8 TmCu1.24 Ge0.76 a
Structure type
CeAl2 Ga2 Ce2 CuGe6 Gd6 Cu8 Ge8 CaIn2
Space group
I4/mmm Amm2 Immm P63 /mmc
Pearson code
tI10 oS18 oI22 hP6
Cell parameters
RI
Rp
0.0557 – 0.0807 0.0603
0.0997 – 0.1172 0.1189
(Å3 )
a (Å)
b (Å)
c (Å)
V
3.99155(8) 4.061(1) 13.7407(3) 4.42254(8)
– 3.957(4) 6.5995(1) –
10.3285(2) 20.76(2) 4.1368(1) 7.0477(2)
164.56(1) 333.6(4) 375.14(3) 108.824(7)
Numbers corresponding to those in Fig. 1.
listed in Table 2. Positional and displacement parameters of the atoms are presented in Table 3, interatomic distances (δ) and coordination numbers (CN) in Table 4. The atomic parameters for the Tm2 CuGe6 ternary compound have not
been refined, because the quality of the experimental X-ray diffraction pattern was not good enough. Thus, only refined lattice parameters for this phase are presented in Table 2. We did not confirm the existence of the ternary compound
Table 3 Atomic coordinates and displacement parameters for TmCu2 Ge2 , Tm6 Cu8 Ge8 and TmCu1.24 Ge0.76 x
y
z
Uiso/eq × 102 (Å2 )
TmCu2 Ge2 (space group I4/mmm) Tm 2(a) Cu 4(e) Ge 4(d)
0 0 0
0 0 1/2
0 0.3823(2) 1/4
0.65(4) 0.64(5) 0.87(6)
Tm6 Cu8 Ge8 (space group Immm) Tm1 2(d) Tm2 4(e) Cu 8(n) Ge1 4(f) Ge2 4(h)
1/2 0.1294(1) 0.3300(2) 0.2156(3) 0
0 0 0.1911(5) 1/2 0.1912(6)
1/2 0 0 0 1/2
0.33(6) 0.10(3) 0.53(7) 0.36(8) 0.45(7)
TmCu1.24 Ge0.76 (space group P63 /mmc) Tm 2(b) Xa 4(f)
0 1/3
0 2/3
1/4 0.4658(4)
0.35(4) 0.72(6)
Atom
a
Position
X = 0.620Cu + 0.380Ge.
L.O. Fedyna et al. / Journal of Alloys and Compounds 367 (2004) 70–75
73
Fig. 2. Experimental (circles) and calculated (continuous lines) powder diffraction profiles and corresponding difference plots (bottom of each figure) for: (a) TmCu2 Ge2 ; (b) Tm6 Cu8 Ge8 ; and (c) TmCu1.24 Ge0.76 . Reflection positions are indicated by vertical bars.
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L.O. Fedyna et al. / Journal of Alloys and Compounds 367 (2004) 70–75
Table 4 Interatomic distances (δ) and coordination numbers (CN) for TmCu2 Ge2 , Tm6 Cu8 Ge8 and TmCu1.24 Ge0.76 Atom
δ (Å)
CN
TmCu2 Ge2 Tm–8Cu Tm–8Ge Tm–4Tm
3.0731(8) 3.2635(2) 3.9915(1)
20
Cu–4Ge Cu–1Cu Cu–4Tm
2.419(1) 2.431(3) 3.0731(8)
9
Ge–4Cu Ge–4Ge Ge–4Tm
2.419(1) 2.8225(1) 3.2635(2)
12
2.873(2) 3.155(2) 3.5238(2)
14
Xa –3Xa Xa –3Tm Xa –1Xa Xa –3Tm
2.4851(8) 2.873(2) 3.042(4) 3.155(2)
10
Tm6 Cu8 Ge8 Tm1–4Ge2 Tm1–2Ge1 Tm1–8Cu Tm1–4Tm2 Tm1–2Tm1
2.904(3) 2.963(4) 3.365(3) 3.7484(9) 4.1368(1)
20
Tm2–4Cu Tm2–2Ge1 Tm2–4Ge2 Tm2–2Cu Tm2–2Ge1 Tm2–1Tm2 Tm2–2Tm1 Tm2–2Tm2
2.957(2) 2.968(3) 3.005(2) 3.031(4) 3.506(1) 3.557(3) 3.7484(9) 4.1368(1)
19
Cu–1Ge2 Cu–2Ge1 Cu–1Cu Cu–1Ge1 Cu–2Tm2 Cu–1Tm2 Cu–2Cu1 Cu–2Tm1
2.461(4) 2.502(2) 2.522(4) 2.574(4) 2.957(2) 3.031(4) 3.118(3) 3.365(3)
12
Ge1–4Cu1 Ge1–2Cu Ge1–1Tm1 Ge1–1Tm2
2.502(2) 2.574(4) 2.963(4) 2.968(3)
8
Ge2–2Cu Ge2–1Ge2 Ge2–2Tm1 Ge2–3Tm2
2.461(4) 2.523(5) 2.904(3) 3.005(2)
8
TmCu1.24 Ge0.76 Tm–6Xa Tm–6Xa Tm–2Tm
a
870 K (equilibrium between Tm0.9 Ge2 and Tm6 Cu8 Ge8 ). This means that the compound with CeNiSi2 -type structure forms at a temperature higher than 870 K. According to literature data, isothermal sections of the phase diagrams were constructed for the R–Cu–Ge systems, where R = Ce [26], Nd [27], Eu [28], Tb [29] and Yb [26]. The Tm–Cu–Ge system is quite similar to the previously investigated Yb–Cu–Ge ternary system in the number of the ternary compounds and their crystal structures, and in the character of the phase equilibria. In both systems four ternary germanides with the same crystal structures form. All compounds have fixed compositions and the solubility of the third component in the binary compounds is incidental. The main discrepancy is the different compositions of the CaIn2 -type ternary compounds: YbCuGe and TmCu1.24 Ge0.76 . In the system Tb–Cu–Ge, the compound TbCuGe (AlB2 type) shows a homogeneity range up to 5 at.% along the line at constant Tb content, and solid solutions of the third components in the TbCu2 and TbGe1.5 binary compounds up to 5 and 20 at.%, respectively, exist. The systems with Ce and Nd contain more ternary compounds: 6 and 8, respectively. The main features of the interaction between the components in the Eu–Cu–Ge system are the crystal structure of the equiatomic compound EuCuGe (structure type TiNiSi) and the homogeneity range of the CeAl2 Ga2 -type compound.
References
X = 0.620Cu + 0.380Ge.
Tm5 CuGe10 (CeNiSi2 type) at 870 K. This phase was found by François et al. [23] at 1170 K, during a study of the formation of CeNiSi2 -type ternary compounds in R–M–Ge systems (R, rare earth metal; M, transition metal). We have investigated the range around this composition more precisely and established that the samples were two-phase at
[1] P.R. Subramanian, D.E. Laughlin, Bull. Alloy Phase Diagrams 9 (1988) 395. [2] V.N. Eremenko, K.A. Meleshevich, Yu.I. Buyanov, P.S. Martsenyuk, Poroshk. Metall. 7 (1989) 41. [3] G. Venturini, I. Ijjaali, B. Malaman, J. Alloys Comp. 284 (1999) 262. [4] G. Venturini, J. Alloys Comp. 308 (2000) 200. [5] R.W. Olesinski, G.J. Abbaschian, Bull. Alloy Phase Diagrams 7 (1986) 28. [6] K.H.J. Buschow, A.S. van der Goot, J. Birkhan, J. Less-Common Met. 19 (1969) 433. [7] A.R. Storm, K.E. Benson, Acta Crystallogr. 16 (1963) 701. [8] A. Iandelli, A. Palenzona, J. Less-Common Met. 9 (1965) 1. [9] E.I. Gladyshevskii, Zh. Strukt. Khim. 5 (1964) 568. [10] O.Ya. Oleksyn, O.I. Bodak, J. Alloys Comp. 210 (1994) 19. [11] A.G. Tharp, G.S. Smith, Q. Johnson, Acta Crystallogr. 20 (1966) 583. [12] G.S. Smith, A.G. Tharp, Q. Johnson, Acta Crystallogr. 22 (1967) 940. [13] E.I. Gladyshevskii, Zh. Strukt. Khim. 5 (1964) 919. [14] J. Lenz, K. Schubert, Z. Metallkd. 62 (1971) 810. [15] W. Burkhardt, K. Schubert, Z. Metallkd. 50 (1959) 442. [16] H. Nowotny, K. Bachmayer, Monatsh. Chem. 81 (1950) 669. [17] H.W. King, T.B. Massalski, L.L. Isaacs, Acta Metall. 11 (1963) 1355. [18] W. Rieger, E. Parthé, Monatsh. Chem. 100 (1969) 444. [19] O. Sologub, K. Hiebl, P. Rogl, O.I. Bodak, J. Alloys Comp. 227 (1995) 37. [20] G. Hanel, H. Nowotny, Monatsh. Chem. 101 (1970) 463. [21] W. Rieger, E. Parthé, Monatsh. Chem. 100 (1969) 439. [22] A. Iandelli, J. Alloys Comp. 198 (1993) 141. [23] M. François, G. Venturini, B. Malaman, B. Roques, J. Less-Common Met. 160 (1990) 197.
L.O. Fedyna et al. / Journal of Alloys and Compounds 367 (2004) 70–75 [24] L.G. Akselrud, P.Yu. Zavalii, Yu.N. Grin, V.K. Pecharsky, B. Baumgartner, E. Wolfel, Mater. Sci. Forum 133–136 (1993) 335. [25] J. Rodriguez-Carvajal, in: Proceedings of the Congress of International Union of Crystallography on Satellite Meeting on Powder Diffraction, Toulouse, 1990, p. 127.
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[26] P.S. Salamakha, M.B. Konyk, R. Dzyanyyi, O.L. Sologub, O.I. Bodak, Pol. J. Chem. 70 (1996) 270. [27] P.S. Salamakha, Visn. Lviv Univ. Ser. Khim. 29 (1988) 62. [28] B.D. Belan, Ph.D. thesis, Lviv University, Lviv, 1988. [29] P.K. Starodub, Ph.D. thesis, Lviv University, Lviv, 1988.
Ternary system Tm–Cu–Ge: isothermal section of the phase diagram at 870 K and crystal structures of the compounds L.O. Fedyna a , O.I. Bodak a,∗ , Ya.O. Tokaychuk a,1 , M.F. Fedyna b , I.R. Mokra a a
Department of Inorganic Chemistry, Ivan Franko National University of L’viv, Kyryla i Mefodiya str. 6, UA-79005 L’viv, Ukraine b Ukrainian State University of Forest and Wood Technology, Chuprynky str. 105, UA-79057 L’viv, Ukraine
Abstract The isothermal section of the Tm–Cu–Ge phase diagram at 870 K was constructed using X-ray phase analysis. The existence of three ternary compounds was confirmed: TmCu2 Ge2 (structure type CeAl2 Ga2 , space group I4/mmm, Pearson code tI10, a = 3.99155(8) Å, c = 10.3285(2) Å), Tm2 CuGe6 (structure type Ce2 CuGe6 , space group Amm2, Pearson code oS18, a = 4.061(1) Å, b = 3.957(4) Å, c = 20.76(2) Å) and Tm6 Cu8 Ge8 (structure type Gd6 Cu8 Ge8 , space group Immm, Pearson code oI22, a = 13.7407(3) Å, b = 6.5995(1) Å, c = 4.1368(1) Å). A new ternary copper germanide TmCu1.24 Ge0.76 (structure type CaIn2 , space group P63 /mmc, Pearson code hP6, a = 4.42254(8) Å, c = 7.0477(2) Å) was found. The crystal structures of TmCu2 Ge2 , Tm6 Cu8 Ge8 and TmCu1.24 Ge0.76 were refined by full-profile Rietveld method using X-ray powder diffraction data. The binary compound Tm0.9 Ge2 (structure type ZrSi2 ) dissolves up to 5 at.% of Cu. The lattice parameters refined for the sample Tm31 Cu5 Ge64 (a = 4.042(1) Å, b = 15.793(4) Å, c = 3.906(2) Å) slightly increased, compared with Tm0.9 Ge2 . The solubility of the third component in the other binary phases was found to be negligible. © 2003 Elsevier B.V. All rights reserved. Keywords: Tm–Cu–Ge; Phase diagram; Isothermal section; Intermetallic compounds; Crystal structure
1. Introduction The binary systems at the boundaries of the Tm–Cu–Ge ternary system have been widely studied and the phase diagrams over the whole concentration regions have been constructed. So, according to [1], five binary compounds form in the Tm–Cu system. The phase diagram of the Tm–Ge system was constructed by Eremenko et al. [2] and eight binary phases have been reported. Recently, Venturini et al. [3] reinvestigated the crystal structure of the non-stoichiometric AlB2 -type compound and reported some new binary TmGe2−x phases, derived from the AlB2 type. The crystal structures of three new TmGe2−x compounds were reported in [4]. According to [5], four intermediate phases exist in the Cu–Ge binary system. Crystallographic data of the binary compounds obtained in these systems are listed in Table 1. The interaction of thulium with copper and germanium has not yet been studied systematically over the ∗
Corresponding author. Tel.: +38-322-742-388. E-mail address: [email protected] (O.I. Bodak). 1 Present address: Laboratoire de Cristallographie, Universit´ e de Gen`eve, quai Ernest-Ansermet 24, CH-1211 Gen`eve, Switzerland. 0925-8388/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2003.08.014
whole concentration range. The existence of ternary compounds, crystallizing with well-known structure types, such as TmCu2 Ge2 (CeAl2 Ga2 type) [18], Tm2 CuGe6 (Ce2 CuGe6 type) [19], Tm6 Cu8 Ge8 (Gd6 Cu8 Ge8 type) [20], TmCu1–0.67 Ge1–1.33 (AlB2 type) [21], TmCuGe (CaIn2 type) [22] and Tm5 CuGe10 (CeNiSi2 type) [23], have been reported. These compounds were synthesized using different techniques and different conditions; no atomic parameters were refined, except for TmCuGe, crystallizing in the AlB2 structure type [21]. The present study was carried out to construct the isothermal section of the phase diagram of the Tm–Cu–Ge system at 870 K, to obtain ternary compounds and determine their crystal structures.
2. Experimental Samples for investigation with the total weight 1 g were prepared from pieces of pure metals (thulium, 99.82 wt.%; copper, 99.90 wt.%; germanium, 99.99 wt.%) by arc melting under purified argon atmosphere under a pressure of 1.1×105 Pa (with Ti as a getter). To ensure homogeneity, the samples were remelted twice. During the sample preparation
L.O. Fedyna et al. / Journal of Alloys and Compounds 367 (2004) 70–75
71
Table 1 Crystallographic data of the binary compounds in the Tm–Cu, Tm–Ge and Cu–Ge systems Compound
Structure type
Space group
TmCu5 Tm2 Cu9 a Tm2 Cu7 a TmCu2 TmCu Tm2 Ge5 a Tm0.9 Ge2 TmGe1.9 a TmGe1.83 a -TmGe2−x a ␣-TmGe2−x a Tm2 Ge3 Tm2 Ge3 a Tm3 Ge4 TmGe Tm11 Ge10 Tm5 Ge4 Tm5 Ge3 Cu5 Ge2 a Cu3 Gea Cu3 Gea
AuBe5 – – KHg2 CsCl Er2 Ge5 ZrSi2 own ErGe1.83 Monoclinicb Monoclinicb AlB2 own Er3 Ge4 CrB Ho11 Ge10 Sm5 Ge4 Mn5 Si3 BiF3 Na3 As Cu3 Ti
F 4¯ 3m – – Imma ¯ Pm3m Pmmn Cmcm Pmma Cmcm
cF23 – – oI12 cP2 oP14 oS12 oP20 oS24
P6/mmm C2/c Cmcm Cmcm I4/mmm Pnma P63 /mcm ¯ Fm3m P63 /mmc Pmmn
hP3 mS20 oS28 oS8 tI84 oP36 hP16 cF16 hP8 oP8
Cu3 Ge
–
P21 /∗
–
2.626 2.633(2)
Cu17 Ge3 a
Mg
P63 /mmc
hP2
2.5923
a b
Pearson code
Cell parameters a (Å)
b (Å)
c (Å)
6.991 – – 4.266 3.415 4.000 4.004 3.879 4.050 3.902 3.8778 3.88 9.0577 3.980 4.185 10.72 7.49 8.31 5.906 4.169 5.28
– – – 6.697 – 3.875 15.713 4.034 29.460 6.705 6.632 – 7.7596 10.490 10.524 – 14.36 – – – 4.22
– – – 7.247 – 18.103 3.864 22.544 3.887 4.075 4.078 4.07 6.6386 14.049 3.885 16.01 7.54 6.23 – 7.499 4.54
4.192 4.203(1) –
4.559 4.553(3) 4.2247
β (◦ )
Reference
– – – – – – – – – 89.79 89.83 – 115.678 – – – – – – – –
[6] [1] [1] [7] [8] [4] [4] [4] [4] [3] [3] [9] [3] [10] [2] [11] [12] [13] [14] [14] [15]
89.41 89.63(8) –
[16] Present work [17]
Compound not observed at 870 K. Monoclinic deformed AlB2 -type structure with ordered Ge vacancies.
the weight losses were less than 1% of the total mass. All samples were annealed in quartz ampoules under vacuum at 870 ± 10 K for 740 h and quenched in cold water. The phase analysis was carried out using X-ray powder diffraction: Debye–Scherrer technique (cameras RKD-57.3, non-filtered Cr K␣ radiation) and DRON-2 powder diffractometer (Fe K␣ radiation). The crystal structures of the ternary compounds were refined from X-ray powder diffraction data, obtained on a DRON-3M diffractometer (Cu K␣ radiation, step scan mode). All procedures, including indexing, refinement of the lattice and atomic parameters and calculations of the interatomic distances, were performed with the CSD [24] and FullProf [25] program packages.
3. Results and discussion Using X-ray phase analysis we have confirmed the existence of 10 intermediate phases in the boundary binary systems at 870 K: Tm0.9 Ge2 (ZrSi2 type), TmGe1.5 (AlB2 type, or a derivative of this type), Tm3 Ge4 (Er3 Ge4 type), Tm11 Ge10 (Ho11 Ge10 type), Tm5 Ge4 (Sm5 Ge4 type), Tm5 Ge3 (Mn5 Si3 type), TmCu5 (AuBe5 type), TmCu2 (KHg2 type), TmCu (CsCl type) and Cu3 Ge. Using profile fitting, the powder pattern of the Cu3 Ge compound was indexed in monoclinic symmetry with lattice constants a = 2.633(2) Å, b = 4.203(1) Å, c = 4.553(3) Å,
β = 89.63(8)◦ , which are in good agreement with literature data [16]. The isothermal section of the phase diagram of the Tm–Cu–Ge ternary system at 870 K is shown in Fig. 1. It was constructed by means of X-ray phase and structural analysis of 90 ternary alloys. The binary germanide Tm0.9 Ge2 dissolves up to 5 at.% Cu. The lattice parameters, refined from X-ray powder data of the sample Tm31 Cu5 Ge64 (a = 4.042(1) Å, b = 15.793(4) Å, c = 3.906(2) Å), slightly increased, compared with Tm0.9 Ge2 (a = 4.004 Å, b = 15.713 Å, c = 3.864 Å) [4]. The other binary compounds do not show appreciable ranges of solubility. The existence of three ternary compounds, TmCu2 Ge2 , Tm2 CuGe6 and Tm6 Cu8 Ge8 , was confirmed in the Tm–Cu–Ge system at 870 K. The formation of these phases at the stoichiometric compositions is in good agreement with literature data. The new ternary compound TmCu1.24 Ge0.76 was obtained in the investigated system at 870 K. The 2θ values and intensities of the reflections in the powder diffraction pattern of the sample Tm34 Cu41 Ge25 indicated that this compound could be isostructural with CaIn2 (space group P63 /mmc). The crystal structures of TmCu2 Ge2 , Tm6 Cu8 Ge8 and TmCu1.24 Ge0.76 were refined by a full-profile Rietveld method using X-ray powder diffraction data. The observed and calculated powder diffraction patterns with difference plots are shown in Fig. 2. The corresponding lattice parameters and R-factors are
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L.O. Fedyna et al. / Journal of Alloys and Compounds 367 (2004) 70–75
870 K
1. TmCu2Ge2 2. Tm2CuGe6 3. Tm6Cu8Ge8 4. TmCu1.24Ge0.76
Tm0.9Ge2 TmGe1.5 Tm3Ge4 Tm11Ge10 Tm5Ge4 Tm5Ge3 Cu3Ge
TmCu5
TmCu2
TmCu
Fig. 1. Isothermal section of the phase diagram of the Tm–Cu–Ge ternary system at 870 K.
Table 2 Crystallographic data of the ternary compounds in the Tm–Cu–Ge system No.a
Compound
1 2 3 4
TmCu2 Ge2 Tm2 CuGe6 Tm6 Cu8 Ge8 TmCu1.24 Ge0.76 a
Structure type
CeAl2 Ga2 Ce2 CuGe6 Gd6 Cu8 Ge8 CaIn2
Space group
I4/mmm Amm2 Immm P63 /mmc
Pearson code
tI10 oS18 oI22 hP6
Cell parameters
RI
Rp
0.0557 – 0.0807 0.0603
0.0997 – 0.1172 0.1189
(Å3 )
a (Å)
b (Å)
c (Å)
V
3.99155(8) 4.061(1) 13.7407(3) 4.42254(8)
– 3.957(4) 6.5995(1) –
10.3285(2) 20.76(2) 4.1368(1) 7.0477(2)
164.56(1) 333.6(4) 375.14(3) 108.824(7)
Numbers corresponding to those in Fig. 1.
listed in Table 2. Positional and displacement parameters of the atoms are presented in Table 3, interatomic distances (δ) and coordination numbers (CN) in Table 4. The atomic parameters for the Tm2 CuGe6 ternary compound have not
been refined, because the quality of the experimental X-ray diffraction pattern was not good enough. Thus, only refined lattice parameters for this phase are presented in Table 2. We did not confirm the existence of the ternary compound
Table 3 Atomic coordinates and displacement parameters for TmCu2 Ge2 , Tm6 Cu8 Ge8 and TmCu1.24 Ge0.76 x
y
z
Uiso/eq × 102 (Å2 )
TmCu2 Ge2 (space group I4/mmm) Tm 2(a) Cu 4(e) Ge 4(d)
0 0 0
0 0 1/2
0 0.3823(2) 1/4
0.65(4) 0.64(5) 0.87(6)
Tm6 Cu8 Ge8 (space group Immm) Tm1 2(d) Tm2 4(e) Cu 8(n) Ge1 4(f) Ge2 4(h)
1/2 0.1294(1) 0.3300(2) 0.2156(3) 0
0 0 0.1911(5) 1/2 0.1912(6)
1/2 0 0 0 1/2
0.33(6) 0.10(3) 0.53(7) 0.36(8) 0.45(7)
TmCu1.24 Ge0.76 (space group P63 /mmc) Tm 2(b) Xa 4(f)
0 1/3
0 2/3
1/4 0.4658(4)
0.35(4) 0.72(6)
Atom
a
Position
X = 0.620Cu + 0.380Ge.
L.O. Fedyna et al. / Journal of Alloys and Compounds 367 (2004) 70–75
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Fig. 2. Experimental (circles) and calculated (continuous lines) powder diffraction profiles and corresponding difference plots (bottom of each figure) for: (a) TmCu2 Ge2 ; (b) Tm6 Cu8 Ge8 ; and (c) TmCu1.24 Ge0.76 . Reflection positions are indicated by vertical bars.
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Table 4 Interatomic distances (δ) and coordination numbers (CN) for TmCu2 Ge2 , Tm6 Cu8 Ge8 and TmCu1.24 Ge0.76 Atom
δ (Å)
CN
TmCu2 Ge2 Tm–8Cu Tm–8Ge Tm–4Tm
3.0731(8) 3.2635(2) 3.9915(1)
20
Cu–4Ge Cu–1Cu Cu–4Tm
2.419(1) 2.431(3) 3.0731(8)
9
Ge–4Cu Ge–4Ge Ge–4Tm
2.419(1) 2.8225(1) 3.2635(2)
12
2.873(2) 3.155(2) 3.5238(2)
14
Xa –3Xa Xa –3Tm Xa –1Xa Xa –3Tm
2.4851(8) 2.873(2) 3.042(4) 3.155(2)
10
Tm6 Cu8 Ge8 Tm1–4Ge2 Tm1–2Ge1 Tm1–8Cu Tm1–4Tm2 Tm1–2Tm1
2.904(3) 2.963(4) 3.365(3) 3.7484(9) 4.1368(1)
20
Tm2–4Cu Tm2–2Ge1 Tm2–4Ge2 Tm2–2Cu Tm2–2Ge1 Tm2–1Tm2 Tm2–2Tm1 Tm2–2Tm2
2.957(2) 2.968(3) 3.005(2) 3.031(4) 3.506(1) 3.557(3) 3.7484(9) 4.1368(1)
19
Cu–1Ge2 Cu–2Ge1 Cu–1Cu Cu–1Ge1 Cu–2Tm2 Cu–1Tm2 Cu–2Cu1 Cu–2Tm1
2.461(4) 2.502(2) 2.522(4) 2.574(4) 2.957(2) 3.031(4) 3.118(3) 3.365(3)
12
Ge1–4Cu1 Ge1–2Cu Ge1–1Tm1 Ge1–1Tm2
2.502(2) 2.574(4) 2.963(4) 2.968(3)
8
Ge2–2Cu Ge2–1Ge2 Ge2–2Tm1 Ge2–3Tm2
2.461(4) 2.523(5) 2.904(3) 3.005(2)
8
TmCu1.24 Ge0.76 Tm–6Xa Tm–6Xa Tm–2Tm
a
870 K (equilibrium between Tm0.9 Ge2 and Tm6 Cu8 Ge8 ). This means that the compound with CeNiSi2 -type structure forms at a temperature higher than 870 K. According to literature data, isothermal sections of the phase diagrams were constructed for the R–Cu–Ge systems, where R = Ce [26], Nd [27], Eu [28], Tb [29] and Yb [26]. The Tm–Cu–Ge system is quite similar to the previously investigated Yb–Cu–Ge ternary system in the number of the ternary compounds and their crystal structures, and in the character of the phase equilibria. In both systems four ternary germanides with the same crystal structures form. All compounds have fixed compositions and the solubility of the third component in the binary compounds is incidental. The main discrepancy is the different compositions of the CaIn2 -type ternary compounds: YbCuGe and TmCu1.24 Ge0.76 . In the system Tb–Cu–Ge, the compound TbCuGe (AlB2 type) shows a homogeneity range up to 5 at.% along the line at constant Tb content, and solid solutions of the third components in the TbCu2 and TbGe1.5 binary compounds up to 5 and 20 at.%, respectively, exist. The systems with Ce and Nd contain more ternary compounds: 6 and 8, respectively. The main features of the interaction between the components in the Eu–Cu–Ge system are the crystal structure of the equiatomic compound EuCuGe (structure type TiNiSi) and the homogeneity range of the CeAl2 Ga2 -type compound.
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