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New intermetallic compounds in the RE–Zn–Al systems and their crystal structure
Journal of Alloys and Compounds 397 (2005) 115–119
New intermetallic compounds in the RE–Zn–Al systems and their crystal structure B. Stel’makhovych, O. Stel’makhovych, Yu. Kuz’ma ∗ Department of Analytical Chemistry, Ivan Franko National University of Lviv, Kyrylo and Mefodij Str. 6, Lviv 79005, Ukraine Received 20 December 2004; accepted 5 January 2005 Available online 23 February 2005
Abstract Crystal structures of some new compounds have been determined using X-ray powder data. The intermetallic compounds YbZn1.75 Al2.25 , SmZn1.62 Al2.38 , NdZn2.34 Al1.66 have the BaAl4 -type structure (s.g. I4/mmm). Other compounds adopt the La3 Al11 -type structure (s.g. Immm): Y3 Zn3.2 Al7.8 , Gd3 Zn3.4 Al7.6 , Tb3 Zn4.6 Al6.4 , Dy3 Zn3.4 Al7.6 , Ho3 Zn4.4 Al6.6 , ∼Er3 Zn4 Al7 , ∼Tm3 Zn4 Al7 . © 2005 Elsevier B.V. All rights reserved. Keywords: Rare-earth intermetallics; Crystal structure; Rare earth metal; X-ray diffraction
Investigating phase equilibria in the Yb–Zn–Al system we discovered a new ternary compound with the composition ∼Yb20 Zn30 Al50 [1]. The ternary intermetallic compounds REZn2 Al2 (RE—La, Ce, Pr, Sm) with the BaAl4 -type structure and composition similar to that of the new compound have been already known from the literature [2–4]. The investigation of the crystal structure of the new compounds and the search for isostructural compounds in other RE–Zn–Al systems (RE—rare earth element) are now the main objectives of our work.
into pellets. After that they were annealed in evacuated quartz ampoules at 700 K for 800 h. The alloys were then quenched in cold water without breaking the ampoules. Phase analysis was carried out using X-ray powder diffraction patterns obtained by the Debye–Scherre technique with nonfiltered Cr K radiation in cameras of 57.3 mm in diameter. The lattice and crystal structure parameters were specified by full-matrix least squares using powder diffraction patterns recorded on a DRON-3M diffractometer (Cu K␣ radiation) using θ–2θ scan technique with steps of 0.02 2θ (2θ max = 120◦ ) and exposition time of 40 s at every point. All calculations were performed using CSD software [5].
2. Experimental
3. Results
We used metal powders of the following purity (wt.%): Al, 99.99; Zn, 99.95; RE (Y, Sm, Nd, Dy, Ho, Er, Tm, Yb, Lu), 99.5. The powders were mixed, compacted into pellets and placed in evacuated quartz ampoules. Then they were slowly heated up to 800 K during 50 h. After cooling the ampoules were broken, the samples were ground into fine-dispersed powder and once again compacted
The diffraction pattern of ∼Yb2 Zn3 Al5 was indexed as a tetragonal unit cell with lattice parameters a = 0.4152 nm, c = 1.1430 nm. This suggests that the new compound crystallizes with a structure of BaAl4 (s.g. I4/mmm) or CaBe2 Ge2 (s.g. P4/nmm)-type. Calculation of the powder diffraction pattern confirmed that the new intermetallic compound belongs to the BaAl4 -structure type. Isostructural compounds with Nd and Sm were also obtained (Tables 1 and 2). The diffraction patterns of the samples with other RE of the yttrium group were similar to that of the investigated
1. Introduction
∗
Corresponding author. E-mail address: [email protected] (Yu. Kuz’ma).
0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.01.033
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B. Stel’makhovych et al. / Journal of Alloys and Compounds 397 (2005) 115–119
Table 1 Lattice parameters and unit cell volumes of the new compounds with BaAl4 - and La3 Al11 -type structure in RE–Zn–Al systems Compound
Y3 Zn3.2 Al7.8 NdZn2.3 Al1.7 SmZn1.62 Al2.38 Gd3 Zn4.6 Al6.4 Tb3 Zn4.6 Al6.4 Dy3 Zn3.4 Al7.6 Ho3 Zn4.4 Al6.6 ∼Er3 Zn4 Al7 ∼Tm3 Zn4 Al7 YbZn1.65 Al2.35 a
ST
La3 Al11 BaAl4 BaAl4 La3 Al11 La3 Al11 La3 Al11 La3 Al11 La3 Al11 La3 Al11 BaAl4
SP
oI28 tI10 tI10 oI28 oI28 oI28 oI28 oI28 oI28 tI10
Lattice parameters (nm) a
b
c
0.42269(1) 0.42013(1) 0.41683(4) 0.42578(2) 0.42422(2) 0.42160(1) 0.42107(1) 0.41973(3) 0.41986(3) 0.412546(8)
1.24676(3)
0.99868(2) 1.09767(5) 1.0998(1) 0.99522(4) 0.99106(5) 0.99922(3) 0.99514(2) 0.99423(9) 0.98741(5) 1.14309(3)
1.25370(6) 1.24722(6) 1.24407(3) 1.23881(3) 1.23304(8) 1.22802(7)
Vc (nm3 )
Va × 102a (nm3 )
0.5263 0.1938 0.1911 0.5313 0.5244 0.5241 0.5191 0.5146 0.5091 0.1946
1.8796 1.9375 1.9109 1.8975 1.8729 1.8718 1.8539 1.8379 1.8182 1.9455
Va = Vc /N.
intermetallic compound Yb(Zn0.41 Al0.59 )4 . However, splitting of reflections with hk0 and hkl indices could indicate an orthorhombic distortion of the tetragonal unit cell. Such a distortion is known and observed in the compounds with La3 Al11 -type structure (s.g. Immm) [6] or CeNi2+x Sb2−x type structure (s.g. Immm) [7,8]. Calculation of the intensities for RE3 (Zn,Al)11 samples (RE—Y, Gd, Tb, Dy, Ho) confirmed that these compounds have La3 Al11 -type structure. The samples with Er and Tm contained significant admixtures of other phases and that is why we could not specify their atomic parameters. The lattice parameters for these compounds are shown in Table 1. Any compounds with La3 Al11 or BaAl4 -type structures in the Lu–Zn–Al system were not found. The atomic parameters of the RE3 (Zn,Al)11 compounds are shown in Table 2. The structures of all the compounds under study are characterized by statistical distribution of the smaller atoms (Zn, Al) in the crystallographic positions. That is why some regions of homogeneity are present. The interatomic distances in the structures of the new compounds are shown in Table 3. A slight shortening of the distances between T2–T2 (BaAl4 -type structure) and T4–T4 (La3 Al11 -type structure) atoms is observed. It constitutes about 13% of the sum of atomic radii of the respective components. It should be noted that such a shortening of the interatomic distances is observed between atoms in crystallographic positions, occupied mostly by the smaller zinc atoms.
Number of atoms in the unit cell of a La3 Al11 -type structure is three times larger minus two smaller atoms comparing with a BaAl4 -type structure unit cell: RE6 X22 = 3RE2 X8 − 2X
(2)
The correlation between the unit cells of La3 Al11 - and BaAl4 -type structures is shown in Fig. 1. Taking into consideration that the investigated compounds form in close concentration ranges (20–21 at.% of RE) we compared volumes occupied by a single atom in a unit cell (Va = Vc /N, Va —averaged volume of one atom, Vc —the unit cell volume, N—number of atoms in a unit cell). Fig. 2 shows that in the Yb(Zn0.41 Al0.59 )4 compound the average volume which is occupied by one atom in a unit cell is nearly 14% larger than the respective values for other compounds. This could indicate intermediate valence of Yb atoms (Yb2+ –Yb3+ ) in the structure of the compound.
Fig. 1. Structural relation between (a) BaAl4 -type and (b) La3 Al11 -type.
4. Discussion BaAl4 - and La3 Al11 -type structures are closely related. The La3 Al11 -type structure is characterized by tripling of one of the smallest lattice parameters of the BaAl4 -type structure: ao ∼ at , bo ∼ 3at , co ∼ ct ,
(1)
where ao , bo co are unit cell parameters of the La3 Al11 -type structure; and at , ct are unit cell parameters of the BaAl4 -type structure.
Fig. 2. The relation between atomic volume and atomic number. (*) Literature data, () results of our investigations.
B. Stel’makhovych et al. / Journal of Alloys and Compounds 397 (2005) 115–119
117
Table 2 Atomic parameters in the structures of RE(Zn,Al)4 compounds (s.g. I4/mmm, BaAl4 -type structure) and RE3 (Zn,Al)11 compounds (s.g. Immm, La3 Al11 -type structure) Atom
Wiskoff position
Coordinates
B × 102 (nm2 )
R
x
y
z
2(a) 4(g) 2(c) 4(j) 8(l) 8(l)
0 0 1/2 1/2 0 0
0 0.3152(1) 1/2 0 0.1455(3) 0.3416(2)
0 0 0 0.7090(5) 0.2716(3) 0.3737(2)
0.21(6) 0.62(5) 1.2(3) 0.8(2) 0.5(1) 0.7(1)
RI = 0.076 RP = 0.110
NdZn2.34 Al1.66 (Nd(Zn0.59 Al0.71 )4 ) 2Nd 2Al T1 (0.68(4)Al + 3.32(4)Zn)
2(a) 4(d) 4(e)
0 0 0
0 1/2 0
0 1/4 0.3891(2)
0.55(4) 0.84(9) 0.87(7)
RI = 0.039 RP = 0.123
SmZn1.68 Al2.32 (Sm(Zn0.42 Al0.58 )4 ) 2Sm 2Al T1 (0.38(4)Al + 3.62(4)Zn)
2(a) 4(d) 4(e)
0 0 0
0 1/2 0
0 1/4 0.3894(3)
0.43(4) 0.7(1) 0.8(2)
RI = 0.055 RP = 0.091
Gd3 Zn3.4 Al7.6 (Gd3 (Zn0.31 Al0.69 )11 ) 2Gd1 4Gd2 2Al T1 (3.40(12)Al + 0.60(12)Zn) T2 (6.40(8)Al + 1.60(8)Zn) T3 (2.64(16)Al + 5.36(16)Zn)
2(a) 4(g) 2(c) 4(j) 8(l) 8(l)
0 0 1/2 1/2 0 0
0 0.3161(3) 1/2 0 0.1468(12) 0.3411(8)
0 0 0 0.713(2) 0.2743(9) 0.3771(6)
0.3(2) 0.2(1) 1.4(7) 1.9(5) 0.7(3) 0.7(2)
RI = 0.075 RP = 0.153
Tb3 Zn4.6 Al6.4 (Tb3 (Zn0.42 Al0.58 )11 ) 2Tb1 4Tb2 2Al T1 (2.44(8)Al + 1.56(8)Zn) T2 (7.12(16)Al + 0.88(16)Zn) T3 (2.08(8)Al + 5.92(8)Zn)
2(a) 4(g) 2(c) 4(j) 8(l) 8(l)
0 0 0 1/2 0 0
0 0.3125(2) 0 0 0.1442(9) 0.3410(6)
0 0 1/2 0.2907(9) 0.2733(8) 0.3747(5)
0.55(9) 0.77(9) 0.9(5) 1.5(3) 1.3(2) 1.1(1)
RI = 0.057 RP = 0.139
Dy3 Zn3.4 Al7.6 (Dy3 (Zn0.31 Al0.69 )11 ) 2Dy1 4Dy2 2Al T1 (3.64(4)Al + 0.36(4)Zn) T2 (7.66(5)Al + 0.36(5)Zn) T3 (1.83(5)Al + 6.17(5)Zn)
2(a) 4(g) 2(c) 4(j) 8(l) 8(l)
0 0 1/2 1/2 0 0
0 0.3155(1) 1/2 0 0.1479(5) 0.3420(3)
0 0 0 0.7109(8) 0.2724(5) 0.3770(2)
0.43(7) 0.24(2) 0.5(2) 0.9(2) 1.1(1) 1.12(7)
RI = 0.048 RP = 0.096
Ho3 Zn4.4 Al6.6 (Ho3 Zn0.40 Al0.60 )11 ) 2Ho1 4Ho2 2Al T1 (3.20(4)Al + 0.80(4)Zn) T2 (7.12(6)Al + 0.88(6)Zn) T3 (0.98(6)Al + 7.02(6)Zn)
2(a) 4(g) 2(c) 4(j) 8(l) 8(l)
0 0 1/2 1/2 0 0
0 0.3133(1) 1/2 0 0.1465(5) 0.3427(3)
0 0 0 0.7085(7) 0.2710(5) 0.3767(2)
0.54(7) 0.47(4) 0.7(2) 0.7(2) 0.75(9) 0.62(6)
RI = 0.049 RP = 0.106
YbZn1.65 Al2.35 (Yb(Zn0.41 Al0.59 )4 ) 2Yb Al (3.78(2)Al + 0.22(2)Zn) T1 (0.92(3)Al + 3.08(3)Zn)
2(a) 4(d) 4(e)
0 0 0
0 1/2 0
0 1/4 0.3911(2)
0.34(3) 0.84(9) 0.77(5)
RI = 0.043 RP = 0.105
Y3 Zn3.2 Al7.8 (Y3 (Zn0.29 Al0.71 )11 ) 2Y1 4Y2 2Al T1 (3.62(4)Al + 0.38(4)Zn) T2 (7.58(5)Al + 0.42(5)Zn) T3 (2.31(5)Al + 5.69(5)Zn)
Our investigation gives an opportunity to analyze a tendency towards formation of compounds with closely related BaAl4 and La3 Al11 structure types in RE–Al binary systems and RE–M–Al ternary systems (M—metals of first and second groups (Cu, Zn, Ag)). Combined data about the formation of intermetallic compounds of these structure types are shown in Table 4. One can see that in RE–Al binary
systems these compounds are typical for RE of the Cegroup only, moreover, the compounds with BaAl4 -type structure appear to be high-temperature modifications, and those with La3 Al11 -type structure, low-temperature modifications. Rare earth metals of the yttrium group do not form binary aluminides, which would belong to any of these structure types.
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Table 3 Interatomic distances (δ, nm) in the structures of the new intermetallic compounds RE(Zn,Al)4 and RE3 (Zn,Al)11 Atom
RE3 (Zn,Al)11
Atom
Y
Gd
Tb
Dy
Ho
RE1–8T3 RE1–4T2 RE1–4T1 RE1–2RE2
0.3158(2) 0.3261(4) 0.3588(4) 0.3930(2)
0.3164(6) 0.3308(13) 0.358(2) 0.3967(4)
0.3157(4) 0.3252(9) 0.3581(9) 0.3897(3)
0.3134(2) 0.3285(6) 0.3573(6) 0.3924(2)
0.3121(2) 0.3252(5) 0.3583(5) 0.3881(2)
RE2–2T1 RE2–2Al RE2–4T3 RE2–4T2 RE2–2T2 RE2–1RE1
0.3113(4) 0.3126(1) 0.3141(2) 0.3151(3) 0.3443(4) 0.3930(2)
0.3141(14) 0.3136(3) 0.3150(7) 0.3136(3) 0.3474(13) 0.3967(4)
0.3124(8) 0.3158(2) 0.3116(5) 0.3136(6) 0.3427(9) 0.3897(3)
0.3119(5) 0.3117(1) 0.3129(2) 0.3133(4) 0.3432(6) 0.3924(2)
Al–4T2 Al–4T1 Al–4RE2
0.2920(4) 0.2975(4) 0.3126(1)
0.2916(13) 0.3010(15) 0.3136(3)
0.2878(9) 0.2964(8) 0.3158(2)
T1–2T3 T1–4T2 T1–2Al T1–2RE2 T1–2RE1
0.2569(4) 0.2794(3) 0.2975(4) 0.3113(4) 0.3588(4)
0.259(2) 0.2815(10) 0.3010(15) 0.3141(14) 0.358(2)
T2–2T3 T2–1T3 T2–2T1 T2–1Al T2–2RE2 T2–1RE1 T2–1RE2
0.2566(2) 0.2644(5) 0.2794(3) 0.2920(4) 0.3151(3) 0.3261(4) 0.3434(4)
T3–1T3 T3–2T2 T3–1T1 T3–1T1 T3–2RE2 T3–2RE1
0.2522(2) 0.2566(2) 0.2569(4) 0.2644(5) 0.3141(2) 0.3158(2)
RE(Zn,Al)4 Sm
Nd
Yb
RE–8T1 RE–8Al RE–4RE
0.3184(2) 0.3469(1) 0.4163
0.3210(1) 0.3456 0.4201
0.3172(1) 0.3524 0.4125
0.3108(5) 0.3128(1) 0.3110(2) 0.3141(3) 0.3397(5) 0.3881(2)
Al–4T1 Al–4Al Al–4RE
0.2586(3) 0.2944 0.3447
0.2597(2) 0.2980 0.3456
0.2618(1) 0.2917 0.3524
0.2922(6) 0.2983(5) 0.3117(1)
0.2914(5) 0.2957(5) 0.3128(1)
T1–1T1 T1–4Al T1–4RE
0.2426(3) 0.2586(3) 0.3184(2)
0.2434(4) 0.2597(2) 0.3210(1)
0.2490(3) 0.2618(1) 0.3172(1)
0.2574(9) 0.2787(6) 0.2964(8) 0.3124(8) 0.3581(9)
0.2571(6) 0.2900(5) 0.2983(5) 0.3119(5) 0.3573(6)
0.2568(5) 0.2788(4) 0.2957(5) 0.3108(5) 0.3583(5)
0.2615(8) 0.265(2) 0.2815(10) 0.2916(13) 0.3137(9) 0.3308(13) 0.3474(13)
0.2585(5) 0.2653(11) 0.2787(6) 0.2878(9) 0.3136(6) 0.3252(9) 0.3427(9)
0.2587(3) 0.2633(7) 0.2800(5) 0.2922(6) 0.3133(4) 0.3285(6) 0.3432(6)
0.2571(3) 0.2646(6) 0.2788(4) 0.2914(5) 0.3141(3) 0.3252(5) 0.3397(5)
0.2463(8) 0.2615(8) 0.259(2) 0.265(2) 0.3150(7) 0.3164(6)
0.2485(6) 0.2585(5) 0.2574(9) 0.2653(11) 0.3116(5) 0.3157(4)
0.2458(3) 0.2587(3) 0.2571(6) 0.2633(7) 0.3129(2) 0.3134(2)
0.2454(3) 0.2571(3) 0.2568(5) 0.2646(6) 0.3110(2) 0.3121(2)
In RE–M–Al ternary systems (M—Cu, Zn, Ag) partial substitution of Al by metals of the first and second groups causes formation of ternary compounds (Table 4). In RE–Zn–Al systems with RE = La, Ce, Pr, Nd, Sm, Yb intermetallic compounds with BaAl4 -type structure are formed, and in systems with RE = Y, Gd, Tb, Dy, Ho, Er, Tm compounds with La3 Al11 -type structure are formed. Since the SmAl4 compound in the Sm–Al system has BaAl4 -type struc-
Table 4 Formation of compounds with the structure of BaAl4 - and La3 Al11 -type in RE–Al and RE–M–Al systems (M—Cu, Zn, Ag)
ture we carried out some additional investigations and discovered that at 700 K the ternary intermetallic compound is not a solid solution of Zn in the SmAl4 binary phase. As one can see in Table 4 ternary compounds with BaAl4 -type structure in RE–M–Al systems form with RE of the Ce-group and Yb, i.e. with RE atoms of lager size (rRE = 0.1802–0.1995 nm [9]). In other ternary systems compounds with the structure of La3 Al11 -type are formed (rRE < 0.1787–0.1724 nm [9]). Obviously, the dimensional factor (rRE /rM ) plays an important, perhaps even a decisive, role in the formation of compounds with BaAl4 - and La3 Al11 -type structure. Given the fact that in RE–Al binary systems for RE of the Ce-group temperature polymorphism is observed, it is possible that partial substitution of Al with M-metal atoms stabilizes the high-temperature modifications (BaAl4 -type structure) reducing the temperature of their polymorphous transformation. It is also possible that at high temperatures these ternary compounds can manifest themselves as solid solutions of Mmetal in REAl4 binary compounds.
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Acknowledgement This work was supported by International Center for Diffraction data (ICDD) (GRANT #01-04 SBM). References [1] O. Stel’makhovych, Yu. Kuz’ma, Interaction between components in system Yb–Zn–Al. III. National Crystal Chemical Conference, Theses, Cernogolovka, 19–23 May 2003, pp. 153–154. [2] A.Z. Ikromov, I.N. Ganiev, A.V. Vakhobov, V.V. Kinzhybalo, Russ. Metall. 5 (1991) 215. [3] A.Z. Ikromov, I.N. Ganiev, V.V. Kinzhybalo, A.V. Vakhobov, B.Ya. Kotur, Russ. Metall. 3. (1990) 219.
119
[4] A.Z. Ikromov, I.N. Ganiev, V.V. Kinzhybalo, Dokl. Akad. Nauk. TSSR 33 (1990) 173. [5] L.G. Akselrud, P.Yu. Zavalii, Yu.N. Grin, V.K. Pecharsky, B. Baumgartner, E. Wolfel, Mater. Sci. Forum 133–136 (1993) 335–340. [6] A.H. Gomes De Mesquito, K.H.J. Buschow, Acta Crystallogr. 22 (1967) 497. [7] V.K. Pecharsky, Yu.B. Pankevych, Dokl. Akad. Nauk. USSR 4 (1982) 46. [8] E.I. Gladyshevsky, O.I. Bodak, V.K. Pecharsky, in: K.A. Gschneidner Jr., L. Eyring (Eds.), Handbook on the Physics and Chemistry of Rare Earth, vol. 13, Elsevier Science Publishers B.V., Amsterdam, 1990, 190 pp. [9] A.F. Holleman, E. Wiberg, Lehrbuch der Anorganischen Chemie, Walter de Gruyter, Berlin, New York, 1995, pp. 1838–1841.
New intermetallic compounds in the RE–Zn–Al systems and their crystal structure B. Stel’makhovych, O. Stel’makhovych, Yu. Kuz’ma ∗ Department of Analytical Chemistry, Ivan Franko National University of Lviv, Kyrylo and Mefodij Str. 6, Lviv 79005, Ukraine Received 20 December 2004; accepted 5 January 2005 Available online 23 February 2005
Abstract Crystal structures of some new compounds have been determined using X-ray powder data. The intermetallic compounds YbZn1.75 Al2.25 , SmZn1.62 Al2.38 , NdZn2.34 Al1.66 have the BaAl4 -type structure (s.g. I4/mmm). Other compounds adopt the La3 Al11 -type structure (s.g. Immm): Y3 Zn3.2 Al7.8 , Gd3 Zn3.4 Al7.6 , Tb3 Zn4.6 Al6.4 , Dy3 Zn3.4 Al7.6 , Ho3 Zn4.4 Al6.6 , ∼Er3 Zn4 Al7 , ∼Tm3 Zn4 Al7 . © 2005 Elsevier B.V. All rights reserved. Keywords: Rare-earth intermetallics; Crystal structure; Rare earth metal; X-ray diffraction
Investigating phase equilibria in the Yb–Zn–Al system we discovered a new ternary compound with the composition ∼Yb20 Zn30 Al50 [1]. The ternary intermetallic compounds REZn2 Al2 (RE—La, Ce, Pr, Sm) with the BaAl4 -type structure and composition similar to that of the new compound have been already known from the literature [2–4]. The investigation of the crystal structure of the new compounds and the search for isostructural compounds in other RE–Zn–Al systems (RE—rare earth element) are now the main objectives of our work.
into pellets. After that they were annealed in evacuated quartz ampoules at 700 K for 800 h. The alloys were then quenched in cold water without breaking the ampoules. Phase analysis was carried out using X-ray powder diffraction patterns obtained by the Debye–Scherre technique with nonfiltered Cr K radiation in cameras of 57.3 mm in diameter. The lattice and crystal structure parameters were specified by full-matrix least squares using powder diffraction patterns recorded on a DRON-3M diffractometer (Cu K␣ radiation) using θ–2θ scan technique with steps of 0.02 2θ (2θ max = 120◦ ) and exposition time of 40 s at every point. All calculations were performed using CSD software [5].
2. Experimental
3. Results
We used metal powders of the following purity (wt.%): Al, 99.99; Zn, 99.95; RE (Y, Sm, Nd, Dy, Ho, Er, Tm, Yb, Lu), 99.5. The powders were mixed, compacted into pellets and placed in evacuated quartz ampoules. Then they were slowly heated up to 800 K during 50 h. After cooling the ampoules were broken, the samples were ground into fine-dispersed powder and once again compacted
The diffraction pattern of ∼Yb2 Zn3 Al5 was indexed as a tetragonal unit cell with lattice parameters a = 0.4152 nm, c = 1.1430 nm. This suggests that the new compound crystallizes with a structure of BaAl4 (s.g. I4/mmm) or CaBe2 Ge2 (s.g. P4/nmm)-type. Calculation of the powder diffraction pattern confirmed that the new intermetallic compound belongs to the BaAl4 -structure type. Isostructural compounds with Nd and Sm were also obtained (Tables 1 and 2). The diffraction patterns of the samples with other RE of the yttrium group were similar to that of the investigated
1. Introduction
∗
Corresponding author. E-mail address: [email protected] (Yu. Kuz’ma).
0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.01.033
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Table 1 Lattice parameters and unit cell volumes of the new compounds with BaAl4 - and La3 Al11 -type structure in RE–Zn–Al systems Compound
Y3 Zn3.2 Al7.8 NdZn2.3 Al1.7 SmZn1.62 Al2.38 Gd3 Zn4.6 Al6.4 Tb3 Zn4.6 Al6.4 Dy3 Zn3.4 Al7.6 Ho3 Zn4.4 Al6.6 ∼Er3 Zn4 Al7 ∼Tm3 Zn4 Al7 YbZn1.65 Al2.35 a
ST
La3 Al11 BaAl4 BaAl4 La3 Al11 La3 Al11 La3 Al11 La3 Al11 La3 Al11 La3 Al11 BaAl4
SP
oI28 tI10 tI10 oI28 oI28 oI28 oI28 oI28 oI28 tI10
Lattice parameters (nm) a
b
c
0.42269(1) 0.42013(1) 0.41683(4) 0.42578(2) 0.42422(2) 0.42160(1) 0.42107(1) 0.41973(3) 0.41986(3) 0.412546(8)
1.24676(3)
0.99868(2) 1.09767(5) 1.0998(1) 0.99522(4) 0.99106(5) 0.99922(3) 0.99514(2) 0.99423(9) 0.98741(5) 1.14309(3)
1.25370(6) 1.24722(6) 1.24407(3) 1.23881(3) 1.23304(8) 1.22802(7)
Vc (nm3 )
Va × 102a (nm3 )
0.5263 0.1938 0.1911 0.5313 0.5244 0.5241 0.5191 0.5146 0.5091 0.1946
1.8796 1.9375 1.9109 1.8975 1.8729 1.8718 1.8539 1.8379 1.8182 1.9455
Va = Vc /N.
intermetallic compound Yb(Zn0.41 Al0.59 )4 . However, splitting of reflections with hk0 and hkl indices could indicate an orthorhombic distortion of the tetragonal unit cell. Such a distortion is known and observed in the compounds with La3 Al11 -type structure (s.g. Immm) [6] or CeNi2+x Sb2−x type structure (s.g. Immm) [7,8]. Calculation of the intensities for RE3 (Zn,Al)11 samples (RE—Y, Gd, Tb, Dy, Ho) confirmed that these compounds have La3 Al11 -type structure. The samples with Er and Tm contained significant admixtures of other phases and that is why we could not specify their atomic parameters. The lattice parameters for these compounds are shown in Table 1. Any compounds with La3 Al11 or BaAl4 -type structures in the Lu–Zn–Al system were not found. The atomic parameters of the RE3 (Zn,Al)11 compounds are shown in Table 2. The structures of all the compounds under study are characterized by statistical distribution of the smaller atoms (Zn, Al) in the crystallographic positions. That is why some regions of homogeneity are present. The interatomic distances in the structures of the new compounds are shown in Table 3. A slight shortening of the distances between T2–T2 (BaAl4 -type structure) and T4–T4 (La3 Al11 -type structure) atoms is observed. It constitutes about 13% of the sum of atomic radii of the respective components. It should be noted that such a shortening of the interatomic distances is observed between atoms in crystallographic positions, occupied mostly by the smaller zinc atoms.
Number of atoms in the unit cell of a La3 Al11 -type structure is three times larger minus two smaller atoms comparing with a BaAl4 -type structure unit cell: RE6 X22 = 3RE2 X8 − 2X
(2)
The correlation between the unit cells of La3 Al11 - and BaAl4 -type structures is shown in Fig. 1. Taking into consideration that the investigated compounds form in close concentration ranges (20–21 at.% of RE) we compared volumes occupied by a single atom in a unit cell (Va = Vc /N, Va —averaged volume of one atom, Vc —the unit cell volume, N—number of atoms in a unit cell). Fig. 2 shows that in the Yb(Zn0.41 Al0.59 )4 compound the average volume which is occupied by one atom in a unit cell is nearly 14% larger than the respective values for other compounds. This could indicate intermediate valence of Yb atoms (Yb2+ –Yb3+ ) in the structure of the compound.
Fig. 1. Structural relation between (a) BaAl4 -type and (b) La3 Al11 -type.
4. Discussion BaAl4 - and La3 Al11 -type structures are closely related. The La3 Al11 -type structure is characterized by tripling of one of the smallest lattice parameters of the BaAl4 -type structure: ao ∼ at , bo ∼ 3at , co ∼ ct ,
(1)
where ao , bo co are unit cell parameters of the La3 Al11 -type structure; and at , ct are unit cell parameters of the BaAl4 -type structure.
Fig. 2. The relation between atomic volume and atomic number. (*) Literature data, () results of our investigations.
B. Stel’makhovych et al. / Journal of Alloys and Compounds 397 (2005) 115–119
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Table 2 Atomic parameters in the structures of RE(Zn,Al)4 compounds (s.g. I4/mmm, BaAl4 -type structure) and RE3 (Zn,Al)11 compounds (s.g. Immm, La3 Al11 -type structure) Atom
Wiskoff position
Coordinates
B × 102 (nm2 )
R
x
y
z
2(a) 4(g) 2(c) 4(j) 8(l) 8(l)
0 0 1/2 1/2 0 0
0 0.3152(1) 1/2 0 0.1455(3) 0.3416(2)
0 0 0 0.7090(5) 0.2716(3) 0.3737(2)
0.21(6) 0.62(5) 1.2(3) 0.8(2) 0.5(1) 0.7(1)
RI = 0.076 RP = 0.110
NdZn2.34 Al1.66 (Nd(Zn0.59 Al0.71 )4 ) 2Nd 2Al T1 (0.68(4)Al + 3.32(4)Zn)
2(a) 4(d) 4(e)
0 0 0
0 1/2 0
0 1/4 0.3891(2)
0.55(4) 0.84(9) 0.87(7)
RI = 0.039 RP = 0.123
SmZn1.68 Al2.32 (Sm(Zn0.42 Al0.58 )4 ) 2Sm 2Al T1 (0.38(4)Al + 3.62(4)Zn)
2(a) 4(d) 4(e)
0 0 0
0 1/2 0
0 1/4 0.3894(3)
0.43(4) 0.7(1) 0.8(2)
RI = 0.055 RP = 0.091
Gd3 Zn3.4 Al7.6 (Gd3 (Zn0.31 Al0.69 )11 ) 2Gd1 4Gd2 2Al T1 (3.40(12)Al + 0.60(12)Zn) T2 (6.40(8)Al + 1.60(8)Zn) T3 (2.64(16)Al + 5.36(16)Zn)
2(a) 4(g) 2(c) 4(j) 8(l) 8(l)
0 0 1/2 1/2 0 0
0 0.3161(3) 1/2 0 0.1468(12) 0.3411(8)
0 0 0 0.713(2) 0.2743(9) 0.3771(6)
0.3(2) 0.2(1) 1.4(7) 1.9(5) 0.7(3) 0.7(2)
RI = 0.075 RP = 0.153
Tb3 Zn4.6 Al6.4 (Tb3 (Zn0.42 Al0.58 )11 ) 2Tb1 4Tb2 2Al T1 (2.44(8)Al + 1.56(8)Zn) T2 (7.12(16)Al + 0.88(16)Zn) T3 (2.08(8)Al + 5.92(8)Zn)
2(a) 4(g) 2(c) 4(j) 8(l) 8(l)
0 0 0 1/2 0 0
0 0.3125(2) 0 0 0.1442(9) 0.3410(6)
0 0 1/2 0.2907(9) 0.2733(8) 0.3747(5)
0.55(9) 0.77(9) 0.9(5) 1.5(3) 1.3(2) 1.1(1)
RI = 0.057 RP = 0.139
Dy3 Zn3.4 Al7.6 (Dy3 (Zn0.31 Al0.69 )11 ) 2Dy1 4Dy2 2Al T1 (3.64(4)Al + 0.36(4)Zn) T2 (7.66(5)Al + 0.36(5)Zn) T3 (1.83(5)Al + 6.17(5)Zn)
2(a) 4(g) 2(c) 4(j) 8(l) 8(l)
0 0 1/2 1/2 0 0
0 0.3155(1) 1/2 0 0.1479(5) 0.3420(3)
0 0 0 0.7109(8) 0.2724(5) 0.3770(2)
0.43(7) 0.24(2) 0.5(2) 0.9(2) 1.1(1) 1.12(7)
RI = 0.048 RP = 0.096
Ho3 Zn4.4 Al6.6 (Ho3 Zn0.40 Al0.60 )11 ) 2Ho1 4Ho2 2Al T1 (3.20(4)Al + 0.80(4)Zn) T2 (7.12(6)Al + 0.88(6)Zn) T3 (0.98(6)Al + 7.02(6)Zn)
2(a) 4(g) 2(c) 4(j) 8(l) 8(l)
0 0 1/2 1/2 0 0
0 0.3133(1) 1/2 0 0.1465(5) 0.3427(3)
0 0 0 0.7085(7) 0.2710(5) 0.3767(2)
0.54(7) 0.47(4) 0.7(2) 0.7(2) 0.75(9) 0.62(6)
RI = 0.049 RP = 0.106
YbZn1.65 Al2.35 (Yb(Zn0.41 Al0.59 )4 ) 2Yb Al (3.78(2)Al + 0.22(2)Zn) T1 (0.92(3)Al + 3.08(3)Zn)
2(a) 4(d) 4(e)
0 0 0
0 1/2 0
0 1/4 0.3911(2)
0.34(3) 0.84(9) 0.77(5)
RI = 0.043 RP = 0.105
Y3 Zn3.2 Al7.8 (Y3 (Zn0.29 Al0.71 )11 ) 2Y1 4Y2 2Al T1 (3.62(4)Al + 0.38(4)Zn) T2 (7.58(5)Al + 0.42(5)Zn) T3 (2.31(5)Al + 5.69(5)Zn)
Our investigation gives an opportunity to analyze a tendency towards formation of compounds with closely related BaAl4 and La3 Al11 structure types in RE–Al binary systems and RE–M–Al ternary systems (M—metals of first and second groups (Cu, Zn, Ag)). Combined data about the formation of intermetallic compounds of these structure types are shown in Table 4. One can see that in RE–Al binary
systems these compounds are typical for RE of the Cegroup only, moreover, the compounds with BaAl4 -type structure appear to be high-temperature modifications, and those with La3 Al11 -type structure, low-temperature modifications. Rare earth metals of the yttrium group do not form binary aluminides, which would belong to any of these structure types.
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Table 3 Interatomic distances (δ, nm) in the structures of the new intermetallic compounds RE(Zn,Al)4 and RE3 (Zn,Al)11 Atom
RE3 (Zn,Al)11
Atom
Y
Gd
Tb
Dy
Ho
RE1–8T3 RE1–4T2 RE1–4T1 RE1–2RE2
0.3158(2) 0.3261(4) 0.3588(4) 0.3930(2)
0.3164(6) 0.3308(13) 0.358(2) 0.3967(4)
0.3157(4) 0.3252(9) 0.3581(9) 0.3897(3)
0.3134(2) 0.3285(6) 0.3573(6) 0.3924(2)
0.3121(2) 0.3252(5) 0.3583(5) 0.3881(2)
RE2–2T1 RE2–2Al RE2–4T3 RE2–4T2 RE2–2T2 RE2–1RE1
0.3113(4) 0.3126(1) 0.3141(2) 0.3151(3) 0.3443(4) 0.3930(2)
0.3141(14) 0.3136(3) 0.3150(7) 0.3136(3) 0.3474(13) 0.3967(4)
0.3124(8) 0.3158(2) 0.3116(5) 0.3136(6) 0.3427(9) 0.3897(3)
0.3119(5) 0.3117(1) 0.3129(2) 0.3133(4) 0.3432(6) 0.3924(2)
Al–4T2 Al–4T1 Al–4RE2
0.2920(4) 0.2975(4) 0.3126(1)
0.2916(13) 0.3010(15) 0.3136(3)
0.2878(9) 0.2964(8) 0.3158(2)
T1–2T3 T1–4T2 T1–2Al T1–2RE2 T1–2RE1
0.2569(4) 0.2794(3) 0.2975(4) 0.3113(4) 0.3588(4)
0.259(2) 0.2815(10) 0.3010(15) 0.3141(14) 0.358(2)
T2–2T3 T2–1T3 T2–2T1 T2–1Al T2–2RE2 T2–1RE1 T2–1RE2
0.2566(2) 0.2644(5) 0.2794(3) 0.2920(4) 0.3151(3) 0.3261(4) 0.3434(4)
T3–1T3 T3–2T2 T3–1T1 T3–1T1 T3–2RE2 T3–2RE1
0.2522(2) 0.2566(2) 0.2569(4) 0.2644(5) 0.3141(2) 0.3158(2)
RE(Zn,Al)4 Sm
Nd
Yb
RE–8T1 RE–8Al RE–4RE
0.3184(2) 0.3469(1) 0.4163
0.3210(1) 0.3456 0.4201
0.3172(1) 0.3524 0.4125
0.3108(5) 0.3128(1) 0.3110(2) 0.3141(3) 0.3397(5) 0.3881(2)
Al–4T1 Al–4Al Al–4RE
0.2586(3) 0.2944 0.3447
0.2597(2) 0.2980 0.3456
0.2618(1) 0.2917 0.3524
0.2922(6) 0.2983(5) 0.3117(1)
0.2914(5) 0.2957(5) 0.3128(1)
T1–1T1 T1–4Al T1–4RE
0.2426(3) 0.2586(3) 0.3184(2)
0.2434(4) 0.2597(2) 0.3210(1)
0.2490(3) 0.2618(1) 0.3172(1)
0.2574(9) 0.2787(6) 0.2964(8) 0.3124(8) 0.3581(9)
0.2571(6) 0.2900(5) 0.2983(5) 0.3119(5) 0.3573(6)
0.2568(5) 0.2788(4) 0.2957(5) 0.3108(5) 0.3583(5)
0.2615(8) 0.265(2) 0.2815(10) 0.2916(13) 0.3137(9) 0.3308(13) 0.3474(13)
0.2585(5) 0.2653(11) 0.2787(6) 0.2878(9) 0.3136(6) 0.3252(9) 0.3427(9)
0.2587(3) 0.2633(7) 0.2800(5) 0.2922(6) 0.3133(4) 0.3285(6) 0.3432(6)
0.2571(3) 0.2646(6) 0.2788(4) 0.2914(5) 0.3141(3) 0.3252(5) 0.3397(5)
0.2463(8) 0.2615(8) 0.259(2) 0.265(2) 0.3150(7) 0.3164(6)
0.2485(6) 0.2585(5) 0.2574(9) 0.2653(11) 0.3116(5) 0.3157(4)
0.2458(3) 0.2587(3) 0.2571(6) 0.2633(7) 0.3129(2) 0.3134(2)
0.2454(3) 0.2571(3) 0.2568(5) 0.2646(6) 0.3110(2) 0.3121(2)
In RE–M–Al ternary systems (M—Cu, Zn, Ag) partial substitution of Al by metals of the first and second groups causes formation of ternary compounds (Table 4). In RE–Zn–Al systems with RE = La, Ce, Pr, Nd, Sm, Yb intermetallic compounds with BaAl4 -type structure are formed, and in systems with RE = Y, Gd, Tb, Dy, Ho, Er, Tm compounds with La3 Al11 -type structure are formed. Since the SmAl4 compound in the Sm–Al system has BaAl4 -type struc-
Table 4 Formation of compounds with the structure of BaAl4 - and La3 Al11 -type in RE–Al and RE–M–Al systems (M—Cu, Zn, Ag)
ture we carried out some additional investigations and discovered that at 700 K the ternary intermetallic compound is not a solid solution of Zn in the SmAl4 binary phase. As one can see in Table 4 ternary compounds with BaAl4 -type structure in RE–M–Al systems form with RE of the Ce-group and Yb, i.e. with RE atoms of lager size (rRE = 0.1802–0.1995 nm [9]). In other ternary systems compounds with the structure of La3 Al11 -type are formed (rRE < 0.1787–0.1724 nm [9]). Obviously, the dimensional factor (rRE /rM ) plays an important, perhaps even a decisive, role in the formation of compounds with BaAl4 - and La3 Al11 -type structure. Given the fact that in RE–Al binary systems for RE of the Ce-group temperature polymorphism is observed, it is possible that partial substitution of Al with M-metal atoms stabilizes the high-temperature modifications (BaAl4 -type structure) reducing the temperature of their polymorphous transformation. It is also possible that at high temperatures these ternary compounds can manifest themselves as solid solutions of Mmetal in REAl4 binary compounds.
B. Stel’makhovych et al. / Journal of Alloys and Compounds 397 (2005) 115–119
Acknowledgement This work was supported by International Center for Diffraction data (ICDD) (GRANT #01-04 SBM). References [1] O. Stel’makhovych, Yu. Kuz’ma, Interaction between components in system Yb–Zn–Al. III. National Crystal Chemical Conference, Theses, Cernogolovka, 19–23 May 2003, pp. 153–154. [2] A.Z. Ikromov, I.N. Ganiev, A.V. Vakhobov, V.V. Kinzhybalo, Russ. Metall. 5 (1991) 215. [3] A.Z. Ikromov, I.N. Ganiev, V.V. Kinzhybalo, A.V. Vakhobov, B.Ya. Kotur, Russ. Metall. 3. (1990) 219.
119
[4] A.Z. Ikromov, I.N. Ganiev, V.V. Kinzhybalo, Dokl. Akad. Nauk. TSSR 33 (1990) 173. [5] L.G. Akselrud, P.Yu. Zavalii, Yu.N. Grin, V.K. Pecharsky, B. Baumgartner, E. Wolfel, Mater. Sci. Forum 133–136 (1993) 335–340. [6] A.H. Gomes De Mesquito, K.H.J. Buschow, Acta Crystallogr. 22 (1967) 497. [7] V.K. Pecharsky, Yu.B. Pankevych, Dokl. Akad. Nauk. USSR 4 (1982) 46. [8] E.I. Gladyshevsky, O.I. Bodak, V.K. Pecharsky, in: K.A. Gschneidner Jr., L. Eyring (Eds.), Handbook on the Physics and Chemistry of Rare Earth, vol. 13, Elsevier Science Publishers B.V., Amsterdam, 1990, 190 pp. [9] A.F. Holleman, E. Wiberg, Lehrbuch der Anorganischen Chemie, Walter de Gruyter, Berlin, New York, 1995, pp. 1838–1841.