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Dy–Cu–Si system at 1170 K
Journal of Alloys and Compounds 437 (2007) 165–168
Dy–Cu–Si system at 1170 K A.V. Morozkin a,∗ , P. Manfrinetti b a b
Department of Chemistry, Moscow Lomonosov State University, Leninskie Gory, GSP-3, Moscow 119899, Russia Dipartimento di Chimica e Chimica Industriale, Universit`a di Genova, Via Dodecaneso 31, 16146 Genova, Italy Received 27 January 2006; received in revised form 25 July 2006; accepted 26 July 2006 Available online 20 September 2006
Abstract The phase equilibria in the Dy–Cu–Si system were investigated by X-ray powder diffraction and local X-ray spectral analysis; the isothermal cross-section at 1170 K was obtained. The following compounds have been confirmed: DyCu2 Si2 [CeGa2 Al2 -type, space group I4/mmm, No. 139, a = 0.3952(1) nm, c = 0.9926(2) nm], DyCu1–0.5 Si1–1.5 [AlB2 -type, space group P6/mmm, No. 191, a = 0.4151(1)–0.3975(1) nm, c = 0.3700(1)–0.4012(1) nm], DyCuSi [ZrBeSi (Ni2 In)-type ordered derived structure, space group P63 /mmc, No. 194, a = 0.4153(1) nm, c = 0.7404(1) nm], Dy3 Cu11 Si4 [Sc3 Ni11 Si4 -type, space group P63 /mmc, No. 194, a = 0.8411(1) nm, c = 0.8814(1) nm] and Dy6 Cu8 Si8 [Gd6 Cu8 Ge8 type, space group Immm, No. 71, a = 1.3665(1) nm, b = 0.6531(1) nm, c = 0.4127(1) nm]. Both phases DyCu0.5 Si1.5 [ThSi2 -type, space group I41 /amd, No. 141-2, a = 0.3985(1) nm, c = 1.3757(3) nm] and Dy33 Cu63 Si4 [CeCu2 -type, space group Imma, No. 74, a = 0.4292(1) nm, b = 0.6832(1) nm, c = 0.7297(2) nm] are pertaining to an extended homogeneity region, being these based on the solid solutions presented by the DySi2 (ThSi2 -type) and DyCu2 (CeCu2 -type) parent binary compounds, respectively. The substitution of Si for Cu stabilizes the high-temperature hexagonal CaCu5 -type modification of the compound DyCu5 ; for this reason, the CaCu5 -type phase Dy17 Cu76 Si7 (space group P6/mmm, No. 191, a = 0.5004(1) nm, c = 0.4085(1) nm) has been observed in this isothermal section, too. © 2006 Elsevier B.V. All rights reserved. Keywords: Rare earth intermetallics; Casting; Dysprosium copper silicides; X-ray diffraction
1. Introduction The interaction between components in the Dy–Si, Dy–Cu and Cu–Si binary systems had been earlier studied in Refs. [1–10]. The formation of a series of metallic phases DyCux , crystallizing with monoclinic superstructures obtained by stacking of cubic structural blocks AB5 (AuBe5 -type) and AB2 (MgCu2 -type) to result in a nearly orthogonal supercells and forming for x = 3.5, 4.0, 4.5, has been also reported [11]; moreover, the existence of the compound Dy3 Si4 (orthorhombic Ho3 Si4 -type) has been more recently published [12] (see Table 1). However, though the formation and lattice constants of four ternary compounds, i.e.: DyCu2 Si2 (CeGa2 Al2 type) [2,3], DyCuSi (AlB2 -type, ZrBeSi-type (Ni2 In-type)) [2,3,13,14], Dy3 Cu11 Si4 (Sc3 Ni11 Si4 -type) [15] and Dy6 Cu8 Si8 (Gd6 Cu8 Ge8 -type) [2,3], were reported earlier (see Table 2), the phase equilibria present in the ternary system Dy–Cu–Si
∗
Corresponding author. E-mail address: [email protected] (A.V. Morozkin).
0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.07.115
have not yet been investigated; this reason has prompted us to undertake this work and here we report the results obtained. 2. Experimental The alloy samples (Fig. 1) were prepared either in an electric-arc furnace, using a non-consumable tungsten electrode, or in induction-heating furnace, on water-cooled copper trays and under a pure argon atmosphere. Copper, silicon (purity of 99.99 and 99.999 wt.%, respectively) and dysprosium (purity 99.9 wt.%) were used as starting components; zirconium was used as an O2 getter during the melting process; the samples were re-melted four times in order to achieve complete fusion and homogeneous composition. The melted alloys were subjected to annealing in evacuated quartz ampoules containing titanium chips as an O2 getter. The ampoules were placed in a resistance furnace and the alloys annealed at 1170 K for a week; the samples were then quenched from the annealing temperature in ice-cold water bath. The phase equilibria in the Dy–Cu–Si system were determined from X-ray phase analysis and local X-ray spectral analysis. A “Camebax” microanalyser was employed to perform local X-ray spectral analysis of the micrographic specimens. Powder X-ray data were obtained on a DRON-3.0 diffractometer (Cu K␣ radiation, 2θ = 10–70◦ , 0.02◦ /step with counting time of 5 s/step). The powder X-ray diffractograms obtained were identified by means of calculated patterns using the RIETAN-program [16] in the isotropic approximation.
166
A.V. Morozkin, P. Manfrinetti / Journal of Alloys and Compounds 437 (2007) 165–168
Table 1 Crystallographic data and temperature of the phase transition of compounds in the Cu–Si, Dy–Cu and Dy–Si systems No.
Compound
Space group
Structure type
a (nm)
Sib Cub
Fd3m Fm3m
C Cu
0.54307 0.36147
3
Dy (LT1) Dy (LT2)b Dy (HT)
Cmcm P63 /mmc Im3m
Mg W
0.3595 0.35903 0.398
4
Cu100–90 Si0–10 b Cu90 Si10 b
Fm3m Fm3m
Cu Cu
0.36134(7)
1 2
b (nm)
0.6183
c (nm)
RF (%)
0.5677 0.56475
Ta (K)
Reference
1683 1357
[1,2] [1,2]
86 1657 1685
[1,2] [1,2] [1,2] [10] c
Cu76 Si24 Cu76 Si24 b Cu76 Si24 Cu76 Si24
¯ R3m ¯ R3m R3¯ Ortho
6 7 8 9 10 11
Cu79 Si21 Cu85.1 Si14.9 d Cu82 Si18 Cu88 Si12 e DyCub DyCu2 b
Cubic Im3m P41 32 P63 /mmc Pm3m Imma
W -Mn Mg CsCl CeCu2
0.6198 0.25543 0.346 0.4303
DyCu5 (HT) DyCu5 b DyCu5 b
P6/mmm ¯ F 43m ¯ F 43m
CaCu5 AuBe5 AuBe5
0.4932 0.7027 0.7030(4)
0.4156
12 13 14 15
Dy2 Cu9 DyCu7 f Dy2 Cu7 g
P4 P6/mmm
0.4299
1.394
TbCu7
16
Dy5 Si3 b Dy5 Si3 b
P63 /mcm P63 /mcm
Mn5 Si3 Mn5 Si3
0.837 0.8386(1)
0.626 0.6281(1)
17
Dy5 Si4
b
Pnma
Sm5 Ge4
0.736
1.448
0.765
[2–4]
18
DySi (HT) DySi (LT)b DySi (LT)b
Pnma Cmcm Cmcm
FeB CrB CrB
0.787 0.4237 0.4240(1)
0.380 1.0494 1.0509(1)
0.565 0.3818 0.3839(1)
[2–4] [2–4]
19 20
Dy3 Si4 b DySi1.67 b
Cmcm P6/mmm
Ho3 Si4 AlB2
0.42107 0.383
2.3892
0.38144 0.411
[12] [2–4]
21
DySi2 (HT)b DySi2 (LT)
I41 /amd Imma
ThSi2 GdSi2
0.403 0.404
1.338 1.334
[2–4] [2–4]
b
5
The reliability factor RF (%) = 100
0.4040 0.4047(1) 0.7000 0.7676
|(I obs ) k k
0.700
0.2437 0.2440(1) 0.7315 0.2194
1130 890–840 830–740
0.9694
1/2
− (Ikcal )
1/2
|)/
|(I obs ) k k
1/2
0.41762 0.6802
0.7282
[10] [10]
980 1125 980 1115 1230 1160
[10] [10] [10] [10] [5] [5]
1240 1200
[5,6] [5] c
6.2
0.394
[10] c
1240 1130 1180
[5] [5,7] [5] [2–4]
3.1
3.8
c
c
| (Ikobs is the integrated intensity evaluated from summation of contribution of the kth
peaks to net observed intensity, Ikobs is the integrated intensity calculated from refined structural parameters). a The listed temperatures refer to a solid phase transition (normal font), to the congruent melting temperature (italic bold font), or to a peritectic temperature (bold font). b The compound belongs to the isothermal cross-section at 1170 K. c This work. d Decomposes at 1130 K. e Decomposes at 825 K. f Decomposes at 1030 K. g Decomposes at 1130 K.
3. Results The results obtained were used in the construction of the isothermal cross-section of the Dy–Cu–Si system at 1170 K; it is presented in Fig. 1. The CeGa2 Al2 -type DyCu2 Si2 , Sc3 Ni11 Si4 -type Dy3 Cu11 Si4 and Gd6 Cu8 Ge8 -type Dy6 Cu8 Si8 compounds were found in the isothermal section at 1170 K and their structure type confirmed.
About what is concerning the structure type of the compound DyCuSi, it appears that it would depend on both the synthesis method and on the subsequent heat treatments of the as-cast alloys. So, the DyCuSi may crystallize in the previously reported AlB2 [2,3], or in the ordered ternary variant ZrBeSi (Ni2 In)-type structures [13,14]. Moreover, on the basis of the results recently obtained for YbCuSi, i.e.: it crystallizes with the LiGaGe-type (ordered ternary derivative of the CaIn2 -type, space group P63 mc, No. 186) [17], we might likely suppose
A.V. Morozkin, P. Manfrinetti / Journal of Alloys and Compounds 437 (2007) 165–168
167
Table 2 Crystallographic data of the ternary compounds in the Dy–Cu–Si system No.
Compound
Space group
Structure type
a (nm)
b (nm)
c (nm)
RF (%)
Reference
0.4085(1) 0.7297(2)
6.9 4.0
a
0.8798 0.8814(1)
5.5
0.413 0.4127(1)
1.8 5.8
1 2
Dy17 Cu76 Si7 Dy33 Cu63 Si4
P6/mmm Imma
CaCu5 CeCu2
0.5004(1) 0.4292(1)
3
Dy3 Cu11 Si4 Dy3 Cu11 Si4
P63 /mmc P63 /mmc
Sc3 Ni11 Si4 Sc3 Ni11 Si4
0.8413 0.8411(1)
4
Dy6 Cu8 Si8 Dy6 Cu8 Si8
Immm Immm
Gd6 Cu8 Ge8 Gd6 Cu8 Ge8
1.369 1.3665(2)
5
DyCu2 Si2 DyCu2 Si2
I4/mmm I4/mmm
CeGa2 Al2 CeGa2 Al2
0.3964 0.3952(1)
0.9982 0.9926(2)
6
DyCuSi DyCuSi DyCuSi DyCuSi
P6/mmm P63 /mmc P63 /mmc P6/mmm
AlB2 ZrBeSi (Ni2 In) ZrBeSi AlB2
0.4019 0.4146 (0.4143) 0.4153(1) 0.4151(1)
0.3913 0.7416 (0.7396) 0.7404(1) 2.1 0.3700(1) 3.0
[2,3] [13,14]
Dy33 Cu23 Si47 Dy33 Cu17 Si50
P6/mmm P6/mmm
AlB2 AlB2
0.4016(1) 0.3975(1)
0.3968(1) 0.4012(1)
3.4 6.1
a
7 8
DyCu0.5 Si1.5
I41 /amd
ThSi2
0.3985(1)
1.3757(3)
6.0
a
The reliability factor RF (%) = 100
k
|(Ikobs )
1/2
− (Ikcal )
1/2
|)/
k
|(Ikobs )
1/2
0.6832(1)
0.653 0.6531(1)
a
[15] a
[2,3] a
[2,3] a
a a
a
| (Ikobs is the integrated intensity evaluated from summation of contribution of the kth
peaks to net observed intensity, Ikcal is the integrated intensity calculated from refined structural parameters). a This work.
DyCuSi to be isotypic, so crystallizing in the same LiGaGe structure type; however, Rietveld refinement attempts on X-ray powder patterns of DyCuSi samples could not unambiguously distinguish between the Ni2 In (ZrBeSi) and LiGaGe structure types. Thus, for this compound we are actually reporting the ordered variant ZrBeSi-type structure; single crystal works are necessary to clarify this point. On the other hand, alloys with out-of-stoichiometric composition (with respect the equiatomic 1:1:1) contain the AlB2 -type phase (Table 2). It appears obvious that the AlB2 -type DyCu1–0.5 Si1–1.5 , ThSi2 -type DyCu0.5 Si1.5 and CeCu2 -type Dy33 Cu63 Si4 phases belong to extended region of solid solubility, starting from
the AlB2 -type DyCu1−x Si1+x , ThSi2 -type DySi2 and CeCu2 type DyCu2 parent compounds, respectively. Both ThSi2 -type Dy2 CuSi3 and AlB2 -type Dy2 CuSi3 compounds were found in the isothermal section at 1170 K. Likely, and similarly to what it has been already observed for the binary compounds in the Dy–Si system, even a very little change in the Dy concentration leads to a change in the structure type of the ternary compounds. The partial substitution of Si for Cu shows to stabilize the hightemperature CaCu5 -type modification of the compound DyCu5 ; for this reason, in this isothermal section Dy17 Cu76 Si7 has been found with the hexagonal CaCu5 -type, also. The other binary compounds do not seem to show any detectable solubility. Acknowledgement This work was supported by the Russian Found for Basic Research through the project No. 06-08-00233-a. References
Fig. 1. Isothermal section at 1170 K of the Dy–Cu–Si system.
[1] J. Emsley, The Elements, 2nd ed., Clarendon Press, Oxford, 1991. [2] Pearson’s Handbook of Crystallographic Data for Intermetallic Phases, vols. 2 and 3, American Society for Metals, Metals Park, OH 44073, 1985, p. 3144. [3] E.I. Gladyshevsky, O.I. Bodak, Kristallokhimia intermetallicheskih soedinenii redkozemel’nyh metallov. L’viv, Vischa shkola, 1982, 252 p. (in Russian). [4] Ph.A. Shank, Struktury dvoinyh splavov, M, Metallurgia, 1973, 760 p. (in Russian). [5] E. Franceschi, J. Less-Common Met. 87 (2) (1982) 249–256. [6] P.R. Subramanian, D.E. Laughlin, Bull. Alloy Phase Diagrams 9 (3a) (1988) 331–337. [7] K.H.J. Buschow, A.S. van der Goot, Acta Crystallogr. B 27 (6) (1971) 1085–1088. [8] J.X. Cheng, Acta Phys. Sin. 31 (6) (1982) 807–809.
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[9] K.H.J. Buschow, A.S. van der Goot, J. Birkhan, J. Less-Common Met. 19 (1969) 433–436. [10] N.P. Liakishev (Ed.), Diagrammy sostoiania dvoinyh metallicheskih sistem, vol. 2, Mashinostroenie, Moscow, 1997, pp. 316–319 (in Russian). [11] R. Cerny, L. Gu´en´ee, R. Wessicken, J. Solid State Chem. 174 (2003) 125–131. [12] J. Roger, T. Guizouarn, K. Hiebl, J.-F. Halet, R. Gu´erin, J. Alloys Compd. 394 (2005) 28–34.
[13] A. Iandelli, J. Less-Common Met. 90 (1983) 121–126. [14] W. Bazela, A. Szytula, J. Leciejewicz, Solid State Commun. 56 (1985) 1043–1045. [15] L. Chornobryvets’, O. Bodak, Visnyk L’viv Univ. Ser. Khim. 39 (2000) 104–106. [16] F. Izumi, in: R.A. Young (Ed.), The Rietveld Method, Oxford University Press, Oxford, 1993 (Chapter 13). [17] P. Manfrinetti, M. Pani, unpublished result.
Dy–Cu–Si system at 1170 K A.V. Morozkin a,∗ , P. Manfrinetti b a b
Department of Chemistry, Moscow Lomonosov State University, Leninskie Gory, GSP-3, Moscow 119899, Russia Dipartimento di Chimica e Chimica Industriale, Universit`a di Genova, Via Dodecaneso 31, 16146 Genova, Italy Received 27 January 2006; received in revised form 25 July 2006; accepted 26 July 2006 Available online 20 September 2006
Abstract The phase equilibria in the Dy–Cu–Si system were investigated by X-ray powder diffraction and local X-ray spectral analysis; the isothermal cross-section at 1170 K was obtained. The following compounds have been confirmed: DyCu2 Si2 [CeGa2 Al2 -type, space group I4/mmm, No. 139, a = 0.3952(1) nm, c = 0.9926(2) nm], DyCu1–0.5 Si1–1.5 [AlB2 -type, space group P6/mmm, No. 191, a = 0.4151(1)–0.3975(1) nm, c = 0.3700(1)–0.4012(1) nm], DyCuSi [ZrBeSi (Ni2 In)-type ordered derived structure, space group P63 /mmc, No. 194, a = 0.4153(1) nm, c = 0.7404(1) nm], Dy3 Cu11 Si4 [Sc3 Ni11 Si4 -type, space group P63 /mmc, No. 194, a = 0.8411(1) nm, c = 0.8814(1) nm] and Dy6 Cu8 Si8 [Gd6 Cu8 Ge8 type, space group Immm, No. 71, a = 1.3665(1) nm, b = 0.6531(1) nm, c = 0.4127(1) nm]. Both phases DyCu0.5 Si1.5 [ThSi2 -type, space group I41 /amd, No. 141-2, a = 0.3985(1) nm, c = 1.3757(3) nm] and Dy33 Cu63 Si4 [CeCu2 -type, space group Imma, No. 74, a = 0.4292(1) nm, b = 0.6832(1) nm, c = 0.7297(2) nm] are pertaining to an extended homogeneity region, being these based on the solid solutions presented by the DySi2 (ThSi2 -type) and DyCu2 (CeCu2 -type) parent binary compounds, respectively. The substitution of Si for Cu stabilizes the high-temperature hexagonal CaCu5 -type modification of the compound DyCu5 ; for this reason, the CaCu5 -type phase Dy17 Cu76 Si7 (space group P6/mmm, No. 191, a = 0.5004(1) nm, c = 0.4085(1) nm) has been observed in this isothermal section, too. © 2006 Elsevier B.V. All rights reserved. Keywords: Rare earth intermetallics; Casting; Dysprosium copper silicides; X-ray diffraction
1. Introduction The interaction between components in the Dy–Si, Dy–Cu and Cu–Si binary systems had been earlier studied in Refs. [1–10]. The formation of a series of metallic phases DyCux , crystallizing with monoclinic superstructures obtained by stacking of cubic structural blocks AB5 (AuBe5 -type) and AB2 (MgCu2 -type) to result in a nearly orthogonal supercells and forming for x = 3.5, 4.0, 4.5, has been also reported [11]; moreover, the existence of the compound Dy3 Si4 (orthorhombic Ho3 Si4 -type) has been more recently published [12] (see Table 1). However, though the formation and lattice constants of four ternary compounds, i.e.: DyCu2 Si2 (CeGa2 Al2 type) [2,3], DyCuSi (AlB2 -type, ZrBeSi-type (Ni2 In-type)) [2,3,13,14], Dy3 Cu11 Si4 (Sc3 Ni11 Si4 -type) [15] and Dy6 Cu8 Si8 (Gd6 Cu8 Ge8 -type) [2,3], were reported earlier (see Table 2), the phase equilibria present in the ternary system Dy–Cu–Si
∗
Corresponding author. E-mail address: [email protected] (A.V. Morozkin).
0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.07.115
have not yet been investigated; this reason has prompted us to undertake this work and here we report the results obtained. 2. Experimental The alloy samples (Fig. 1) were prepared either in an electric-arc furnace, using a non-consumable tungsten electrode, or in induction-heating furnace, on water-cooled copper trays and under a pure argon atmosphere. Copper, silicon (purity of 99.99 and 99.999 wt.%, respectively) and dysprosium (purity 99.9 wt.%) were used as starting components; zirconium was used as an O2 getter during the melting process; the samples were re-melted four times in order to achieve complete fusion and homogeneous composition. The melted alloys were subjected to annealing in evacuated quartz ampoules containing titanium chips as an O2 getter. The ampoules were placed in a resistance furnace and the alloys annealed at 1170 K for a week; the samples were then quenched from the annealing temperature in ice-cold water bath. The phase equilibria in the Dy–Cu–Si system were determined from X-ray phase analysis and local X-ray spectral analysis. A “Camebax” microanalyser was employed to perform local X-ray spectral analysis of the micrographic specimens. Powder X-ray data were obtained on a DRON-3.0 diffractometer (Cu K␣ radiation, 2θ = 10–70◦ , 0.02◦ /step with counting time of 5 s/step). The powder X-ray diffractograms obtained were identified by means of calculated patterns using the RIETAN-program [16] in the isotropic approximation.
166
A.V. Morozkin, P. Manfrinetti / Journal of Alloys and Compounds 437 (2007) 165–168
Table 1 Crystallographic data and temperature of the phase transition of compounds in the Cu–Si, Dy–Cu and Dy–Si systems No.
Compound
Space group
Structure type
a (nm)
Sib Cub
Fd3m Fm3m
C Cu
0.54307 0.36147
3
Dy (LT1) Dy (LT2)b Dy (HT)
Cmcm P63 /mmc Im3m
Mg W
0.3595 0.35903 0.398
4
Cu100–90 Si0–10 b Cu90 Si10 b
Fm3m Fm3m
Cu Cu
0.36134(7)
1 2
b (nm)
0.6183
c (nm)
RF (%)
0.5677 0.56475
Ta (K)
Reference
1683 1357
[1,2] [1,2]
86 1657 1685
[1,2] [1,2] [1,2] [10] c
Cu76 Si24 Cu76 Si24 b Cu76 Si24 Cu76 Si24
¯ R3m ¯ R3m R3¯ Ortho
6 7 8 9 10 11
Cu79 Si21 Cu85.1 Si14.9 d Cu82 Si18 Cu88 Si12 e DyCub DyCu2 b
Cubic Im3m P41 32 P63 /mmc Pm3m Imma
W -Mn Mg CsCl CeCu2
0.6198 0.25543 0.346 0.4303
DyCu5 (HT) DyCu5 b DyCu5 b
P6/mmm ¯ F 43m ¯ F 43m
CaCu5 AuBe5 AuBe5
0.4932 0.7027 0.7030(4)
0.4156
12 13 14 15
Dy2 Cu9 DyCu7 f Dy2 Cu7 g
P4 P6/mmm
0.4299
1.394
TbCu7
16
Dy5 Si3 b Dy5 Si3 b
P63 /mcm P63 /mcm
Mn5 Si3 Mn5 Si3
0.837 0.8386(1)
0.626 0.6281(1)
17
Dy5 Si4
b
Pnma
Sm5 Ge4
0.736
1.448
0.765
[2–4]
18
DySi (HT) DySi (LT)b DySi (LT)b
Pnma Cmcm Cmcm
FeB CrB CrB
0.787 0.4237 0.4240(1)
0.380 1.0494 1.0509(1)
0.565 0.3818 0.3839(1)
[2–4] [2–4]
19 20
Dy3 Si4 b DySi1.67 b
Cmcm P6/mmm
Ho3 Si4 AlB2
0.42107 0.383
2.3892
0.38144 0.411
[12] [2–4]
21
DySi2 (HT)b DySi2 (LT)
I41 /amd Imma
ThSi2 GdSi2
0.403 0.404
1.338 1.334
[2–4] [2–4]
b
5
The reliability factor RF (%) = 100
0.4040 0.4047(1) 0.7000 0.7676
|(I obs ) k k
0.700
0.2437 0.2440(1) 0.7315 0.2194
1130 890–840 830–740
0.9694
1/2
− (Ikcal )
1/2
|)/
|(I obs ) k k
1/2
0.41762 0.6802
0.7282
[10] [10]
980 1125 980 1115 1230 1160
[10] [10] [10] [10] [5] [5]
1240 1200
[5,6] [5] c
6.2
0.394
[10] c
1240 1130 1180
[5] [5,7] [5] [2–4]
3.1
3.8
c
c
| (Ikobs is the integrated intensity evaluated from summation of contribution of the kth
peaks to net observed intensity, Ikobs is the integrated intensity calculated from refined structural parameters). a The listed temperatures refer to a solid phase transition (normal font), to the congruent melting temperature (italic bold font), or to a peritectic temperature (bold font). b The compound belongs to the isothermal cross-section at 1170 K. c This work. d Decomposes at 1130 K. e Decomposes at 825 K. f Decomposes at 1030 K. g Decomposes at 1130 K.
3. Results The results obtained were used in the construction of the isothermal cross-section of the Dy–Cu–Si system at 1170 K; it is presented in Fig. 1. The CeGa2 Al2 -type DyCu2 Si2 , Sc3 Ni11 Si4 -type Dy3 Cu11 Si4 and Gd6 Cu8 Ge8 -type Dy6 Cu8 Si8 compounds were found in the isothermal section at 1170 K and their structure type confirmed.
About what is concerning the structure type of the compound DyCuSi, it appears that it would depend on both the synthesis method and on the subsequent heat treatments of the as-cast alloys. So, the DyCuSi may crystallize in the previously reported AlB2 [2,3], or in the ordered ternary variant ZrBeSi (Ni2 In)-type structures [13,14]. Moreover, on the basis of the results recently obtained for YbCuSi, i.e.: it crystallizes with the LiGaGe-type (ordered ternary derivative of the CaIn2 -type, space group P63 mc, No. 186) [17], we might likely suppose
A.V. Morozkin, P. Manfrinetti / Journal of Alloys and Compounds 437 (2007) 165–168
167
Table 2 Crystallographic data of the ternary compounds in the Dy–Cu–Si system No.
Compound
Space group
Structure type
a (nm)
b (nm)
c (nm)
RF (%)
Reference
0.4085(1) 0.7297(2)
6.9 4.0
a
0.8798 0.8814(1)
5.5
0.413 0.4127(1)
1.8 5.8
1 2
Dy17 Cu76 Si7 Dy33 Cu63 Si4
P6/mmm Imma
CaCu5 CeCu2
0.5004(1) 0.4292(1)
3
Dy3 Cu11 Si4 Dy3 Cu11 Si4
P63 /mmc P63 /mmc
Sc3 Ni11 Si4 Sc3 Ni11 Si4
0.8413 0.8411(1)
4
Dy6 Cu8 Si8 Dy6 Cu8 Si8
Immm Immm
Gd6 Cu8 Ge8 Gd6 Cu8 Ge8
1.369 1.3665(2)
5
DyCu2 Si2 DyCu2 Si2
I4/mmm I4/mmm
CeGa2 Al2 CeGa2 Al2
0.3964 0.3952(1)
0.9982 0.9926(2)
6
DyCuSi DyCuSi DyCuSi DyCuSi
P6/mmm P63 /mmc P63 /mmc P6/mmm
AlB2 ZrBeSi (Ni2 In) ZrBeSi AlB2
0.4019 0.4146 (0.4143) 0.4153(1) 0.4151(1)
0.3913 0.7416 (0.7396) 0.7404(1) 2.1 0.3700(1) 3.0
[2,3] [13,14]
Dy33 Cu23 Si47 Dy33 Cu17 Si50
P6/mmm P6/mmm
AlB2 AlB2
0.4016(1) 0.3975(1)
0.3968(1) 0.4012(1)
3.4 6.1
a
7 8
DyCu0.5 Si1.5
I41 /amd
ThSi2
0.3985(1)
1.3757(3)
6.0
a
The reliability factor RF (%) = 100
k
|(Ikobs )
1/2
− (Ikcal )
1/2
|)/
k
|(Ikobs )
1/2
0.6832(1)
0.653 0.6531(1)
a
[15] a
[2,3] a
[2,3] a
a a
a
| (Ikobs is the integrated intensity evaluated from summation of contribution of the kth
peaks to net observed intensity, Ikcal is the integrated intensity calculated from refined structural parameters). a This work.
DyCuSi to be isotypic, so crystallizing in the same LiGaGe structure type; however, Rietveld refinement attempts on X-ray powder patterns of DyCuSi samples could not unambiguously distinguish between the Ni2 In (ZrBeSi) and LiGaGe structure types. Thus, for this compound we are actually reporting the ordered variant ZrBeSi-type structure; single crystal works are necessary to clarify this point. On the other hand, alloys with out-of-stoichiometric composition (with respect the equiatomic 1:1:1) contain the AlB2 -type phase (Table 2). It appears obvious that the AlB2 -type DyCu1–0.5 Si1–1.5 , ThSi2 -type DyCu0.5 Si1.5 and CeCu2 -type Dy33 Cu63 Si4 phases belong to extended region of solid solubility, starting from
the AlB2 -type DyCu1−x Si1+x , ThSi2 -type DySi2 and CeCu2 type DyCu2 parent compounds, respectively. Both ThSi2 -type Dy2 CuSi3 and AlB2 -type Dy2 CuSi3 compounds were found in the isothermal section at 1170 K. Likely, and similarly to what it has been already observed for the binary compounds in the Dy–Si system, even a very little change in the Dy concentration leads to a change in the structure type of the ternary compounds. The partial substitution of Si for Cu shows to stabilize the hightemperature CaCu5 -type modification of the compound DyCu5 ; for this reason, in this isothermal section Dy17 Cu76 Si7 has been found with the hexagonal CaCu5 -type, also. The other binary compounds do not seem to show any detectable solubility. Acknowledgement This work was supported by the Russian Found for Basic Research through the project No. 06-08-00233-a. References
Fig. 1. Isothermal section at 1170 K of the Dy–Cu–Si system.
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