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REInCd, REAsPd and RESbPt compounds (RE ≡ rare earth element)
Pl
Metals, 78 (1981) Pl - P5
Journal of the Less-Common
REInCd, REAsPd AND RESbPt COMPOUNDS (RE ? RARE EARTH ELEMENT)
D. ROSSI, R. MARAZZA,
D. MAZZONE and R. FERRO
Zstituto di Chimica Generale ed Znorganica, Universitd di Genova, Genoa (Italy) (Received August 5,198O)
Summary The structuraI characteristics of a number of REInCd compounds (RE I rare earth) and of the REAsPd and RESbPt compounds with the light rare earths were studied. These compounds have the hP6 CaIn&.ype structure. The average atomic volumes are compared with those of other isostructural rare earth alloys and with those of a number of phases having the same formula but the cF12 MgAgAs-type structure.
1. Introduction It is known that a number of compounds having a valence electron concentration close to 8/3 and a 1:2 or 1:l: 1 stoichiometry crystahize in the hP6 CaInz-type structure. Among the binary compounds of this type are CaGas, CaInz, SrInz, SrTlz, BaTl,, EuIna, EuTla, YbGaz, YbInz and ThHg, [l, 21. Examples of ternary compounds are ZrGaCu, HfGaCu and USnPd [ 2,3] and a series of 1:l:l compounds recently described by Dwight [ 41 (RESnCu phases for ah the rare earths except lanthanum and RESnAu phases for the light rare earths from cerium to hohnium). As part of our investigation of the ternary alloys of the rare earths, we have described previously a few compounds having the formula RESbPd [5] : these have the hP6 CaInz-type structure for RE = La, Ce, Pr, Nd, Sm, Gd, Tb and the cF12 MgAgAs-type structure for RE c Dy, Ho, Er, Yb, Y (i.e. the same structure as the RESnAu phases of the heavy rare earths). In the series of 1:l:l compounds of the rare earths, the CaIna-type phases and those having the MgAgAs-type structure can be considered as competing phases as far as their relative stability is concerned. In addition to the compounds already mentioned, the following series of phases have the MgAgAs-type structure: RESbNi [6] (identified for RE = Gd - Lu); REBiNi ES] (compounds have been prepared for RE = Cd, Dy, Ho, Tm, Lu); REBiPd [7] (for RE = Ce, Nd, Gd, Dy, Ho, Yb); REBiPt [6, 71 (RE s Ce, Gd, Dy,Ho, Er, Yb); RESnAu [4] (for RE = Ho - Lu). 0022-5088/81/0000-00001$02.50
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In this paper we report the results obtained for REAsPd and RESbPt alloys (with a few light rare earths) and for the REInCd compounds. These alloys were all found to have the hP6 CaIna-type structure. 2. Experimental The metals used had purities of around 99.9% for the rare earths and around 99.99% for the others. The samples (each about 1 - 2 g), enclosed in tantalum vessels under an argon atmosphere, were prepared by melting in an induction furnace; after rapid cooling they were then annealed at 500 “C for a week. They were examined with a metallographic microscope after etching either in HNOs + HCl (for alloys with palladium and arsenic or platinum and antimony) or in HNOe diluted in CaH,OH (for alloys with indium and cadmium ) .
X-ray powder photographs were taken with Fe Ka and Cu Ka radiations. The lattice constants were refined by the least-squares method using the Nelson-Riley function. The intensities, visually estimated from the films, were compared with the calculated values.
3. Results In general the alloys appeared as small well-melted ingots which were fragile and homogeneous around the nominal composition 1: 1: 1. The data obtained for their hexagonal cells are listed in Tables 1 and 2. As previously mentioned, the alloys had the hexagonal hP6 CaIna-type structure with the following atomic positions in space group P63/mmc (No. 194): 2 RE in (b) (0, 0, i); 2 Me and 2 X in (f) (i, f, z) Me = In, As, Sb; X = Cd, Pd, Pt). On the basis of this structure, good agreement was obtained between the intensities observed and those computed with z = 0.040 - 0.045. The average atomic volumes of the alloys are reported in Fig. 1 in the order of the atomic number of the rare earth element, together with the previously known values of a number of phases having CaInz- or MgAgAstype structures. 3.1. REInCd alloys For these alloys we observe (Fig. 1) for the trivalent rare earths a regular trend of the atomic volume versus the rare earth atomic number. We note also the sharp deviation from this trend which occurs for the ytterbium compound. 3.1,l. Sm-In-Cd alloys For the Sm-In-Cd alloys a number of samples were also prepared for a few compositions which differed from the ideal 1:l:l stoichiometry. The
P3 TABLE 1 Crystai data for ternary REInCd alloys of the hP6 CaIng type Compound LaInCd CeInCd PrInCd NdInCd SmInCd GdInCd DyInCd HoInCd ErInCd YbInCd
a
C
(kO.003 A)
(iO.005
4.936 4.943 4.907
7.652 7.809 7.609 7.572 7.469 7.398 7.318 7.301 7.253 7.302
4.689
4.866 4.845 4.819 4.805 4.796 4.948
A)
b
V”
c/a
1.550 1.580 1.551 1.549 1.535 1.527 1.519 1.519 1.512 1.476
(A31
;;
4 -3 &cm 1
26.9
5.2 -0.6 3.6 4.4 5.3 6.9 7.2 7.5 7.9 13.0
7.53 7.3s 7.70 7.8, 8.1, 8.49 8.79 8.9g 9.06 8.5s
27.5 26.5 26.1 25.5 25.1 24.5 24.3 24.1 25.8
*Average atomic volume v= V bAv (%) = loo( Xv at - v Cdl ),c&$6’ at* TABLE 2 Crystal data for ternary REAsPd and RESbPt alloys of the hP6 CaIng type A)
DX (g cme3)
Compound
a (+ 0.003 A)
c (t0.005
CeAsPdb PrAsPd NdAaPd
4.37 4.355 4.344
7.80 7.709 7.682
1.77 1.770 1.768
21.5 21.1 20.9
LaSbPt CeSbPt NdSbPt
4.560 4.550 4.544
8.263 8.077 7.878
1.812 1.775 1.734
24.8 24.1 23.5
c/a
8.2, 8.4s 8.6, 10.1, 10.4, 10.8,
‘Average atomic volume 7 = Vcen/6. bHeterogeneous sample.
lattice parameter variation observed (which has a very complex trend as a function of composition) suggests the existence of a certain range of solid solutions. The values of the lattice parameters are generally in the fo_llowing ranges: a = 4.68 - 4.89 A; c = 7.34 - 7.48 A; average atomic volume V = 23.3 - 25.5 A3.The homogeneity field for the 1:l:l composition extends preferentially into the samarium-rich region in a direction parallel to the CdIn axis. 3.2. REAsPd alloys The data relevant to these alloys are given in Table 2. Data for the light rare earths only are reported, since results obtained from samples prepared with the heavier rare earths could not be clearly interpreted. Generally these
LaCePr
NdPmSmEuGdTbDyHoEr
TmYb
Lu
Fig. 1. The average atomic volume of the REMeX compounds ~8. the atomic number of the rare earth: v, 0, n, $0, phases with the hP6 CaIng-type structure;A,V, O,n, phases with the cF12 MgAgAs-type structure (for the polymorphic compound HoSnAu both structural types have been identified [ 4 ] ).
samples were he~rogeneous and in their powder photo~aphs only the caption lines of the binary REAs compound were identified. 3.3. RESbPt alloys In Fig. 1 data are plotted both for the compounds prepared with the light rare earths (of the CaIns type) and for the compounds with the heavy rare earths (which have the MgAgAs-type structure [6] ). During this work the SmSbPt compound was also prepared: it had the cF12 MgAgAs-type structure with a = 6.554 A. The volume variation that we observe in the RESbPt series, on passing from the CaIna-type phases to those having the MgAgAs-type structure, may be usefully compared with the analogous trend shown by the RESbPd and RESnAu alloys (both corresponding to a nominal valence electron concentration of 8f3). In these series also we observe the MgAgAs-type structure for the compounds of the heavy rare earths and the
P5
CaIn&ype structure for the lighter rare earths. The possible reasons for the preferential stability of the less dense MgAgAs-type structure with the rare earths having smaller atomic dimensions have been discussed previously [4,
51. References 1 A. Iandelli, 2. Anorg. Chem., 330 (1964) 121. 2 P. Eckerlin and H. Kandler (eds.), Landolt-Biirnstein, Zahlenwerte und Funktionen aus Naturwissenschaften und Technik, Group III, Vol. 6, Structurdaten der Elemente und intermetallische Phasen, Springer, Berlin, 1971. 3 A. E. Dwight, Winter Meeting of the American Crystallographic Association, Columbia, 19 71, personal communication. 4 A. E. Dwight, in C. E. Lundin (ea.), Proc. 12th Rare Earth Research Conf., Vail, Colomdo, July 18 - 22, 1976, Denver Research Institute, pp. 480 - 489. 5 R. Marazza, D. Rossi and R. Ferro, J. Less-Common Met., 75 (1980) P25. 6 A. E. Dwight, in J. M. Haschke and H. Eick (eds.), Proc. 1 lth Rare Earth Research Conf., Traverse City, Michigan, October 7 - 10, 1974, Vol. 2, p. 642 7 R. Marazza, D. Rossi and R. Ferro, Gazz. Chim. Ital., 110 (1980) 357.
Metals, 78 (1981) Pl - P5
Journal of the Less-Common
REInCd, REAsPd AND RESbPt COMPOUNDS (RE ? RARE EARTH ELEMENT)
D. ROSSI, R. MARAZZA,
D. MAZZONE and R. FERRO
Zstituto di Chimica Generale ed Znorganica, Universitd di Genova, Genoa (Italy) (Received August 5,198O)
Summary The structuraI characteristics of a number of REInCd compounds (RE I rare earth) and of the REAsPd and RESbPt compounds with the light rare earths were studied. These compounds have the hP6 CaIn&.ype structure. The average atomic volumes are compared with those of other isostructural rare earth alloys and with those of a number of phases having the same formula but the cF12 MgAgAs-type structure.
1. Introduction It is known that a number of compounds having a valence electron concentration close to 8/3 and a 1:2 or 1:l: 1 stoichiometry crystahize in the hP6 CaInz-type structure. Among the binary compounds of this type are CaGas, CaInz, SrInz, SrTlz, BaTl,, EuIna, EuTla, YbGaz, YbInz and ThHg, [l, 21. Examples of ternary compounds are ZrGaCu, HfGaCu and USnPd [ 2,3] and a series of 1:l:l compounds recently described by Dwight [ 41 (RESnCu phases for ah the rare earths except lanthanum and RESnAu phases for the light rare earths from cerium to hohnium). As part of our investigation of the ternary alloys of the rare earths, we have described previously a few compounds having the formula RESbPd [5] : these have the hP6 CaInz-type structure for RE = La, Ce, Pr, Nd, Sm, Gd, Tb and the cF12 MgAgAs-type structure for RE c Dy, Ho, Er, Yb, Y (i.e. the same structure as the RESnAu phases of the heavy rare earths). In the series of 1:l:l compounds of the rare earths, the CaIna-type phases and those having the MgAgAs-type structure can be considered as competing phases as far as their relative stability is concerned. In addition to the compounds already mentioned, the following series of phases have the MgAgAs-type structure: RESbNi [6] (identified for RE = Gd - Lu); REBiNi ES] (compounds have been prepared for RE = Cd, Dy, Ho, Tm, Lu); REBiPd [7] (for RE = Ce, Nd, Gd, Dy, Ho, Yb); REBiPt [6, 71 (RE s Ce, Gd, Dy,Ho, Er, Yb); RESnAu [4] (for RE = Ho - Lu). 0022-5088/81/0000-00001$02.50
0 Elsevier Sequoia/Printed
in The Netherlands
P2
In this paper we report the results obtained for REAsPd and RESbPt alloys (with a few light rare earths) and for the REInCd compounds. These alloys were all found to have the hP6 CaIna-type structure. 2. Experimental The metals used had purities of around 99.9% for the rare earths and around 99.99% for the others. The samples (each about 1 - 2 g), enclosed in tantalum vessels under an argon atmosphere, were prepared by melting in an induction furnace; after rapid cooling they were then annealed at 500 “C for a week. They were examined with a metallographic microscope after etching either in HNOs + HCl (for alloys with palladium and arsenic or platinum and antimony) or in HNOe diluted in CaH,OH (for alloys with indium and cadmium ) .
X-ray powder photographs were taken with Fe Ka and Cu Ka radiations. The lattice constants were refined by the least-squares method using the Nelson-Riley function. The intensities, visually estimated from the films, were compared with the calculated values.
3. Results In general the alloys appeared as small well-melted ingots which were fragile and homogeneous around the nominal composition 1: 1: 1. The data obtained for their hexagonal cells are listed in Tables 1 and 2. As previously mentioned, the alloys had the hexagonal hP6 CaIna-type structure with the following atomic positions in space group P63/mmc (No. 194): 2 RE in (b) (0, 0, i); 2 Me and 2 X in (f) (i, f, z) Me = In, As, Sb; X = Cd, Pd, Pt). On the basis of this structure, good agreement was obtained between the intensities observed and those computed with z = 0.040 - 0.045. The average atomic volumes of the alloys are reported in Fig. 1 in the order of the atomic number of the rare earth element, together with the previously known values of a number of phases having CaInz- or MgAgAstype structures. 3.1. REInCd alloys For these alloys we observe (Fig. 1) for the trivalent rare earths a regular trend of the atomic volume versus the rare earth atomic number. We note also the sharp deviation from this trend which occurs for the ytterbium compound. 3.1,l. Sm-In-Cd alloys For the Sm-In-Cd alloys a number of samples were also prepared for a few compositions which differed from the ideal 1:l:l stoichiometry. The
P3 TABLE 1 Crystai data for ternary REInCd alloys of the hP6 CaIng type Compound LaInCd CeInCd PrInCd NdInCd SmInCd GdInCd DyInCd HoInCd ErInCd YbInCd
a
C
(kO.003 A)
(iO.005
4.936 4.943 4.907
7.652 7.809 7.609 7.572 7.469 7.398 7.318 7.301 7.253 7.302
4.689
4.866 4.845 4.819 4.805 4.796 4.948
A)
b
V”
c/a
1.550 1.580 1.551 1.549 1.535 1.527 1.519 1.519 1.512 1.476
(A31
;;
4 -3 &cm 1
26.9
5.2 -0.6 3.6 4.4 5.3 6.9 7.2 7.5 7.9 13.0
7.53 7.3s 7.70 7.8, 8.1, 8.49 8.79 8.9g 9.06 8.5s
27.5 26.5 26.1 25.5 25.1 24.5 24.3 24.1 25.8
*Average atomic volume v= V bAv (%) = loo( Xv at - v Cdl ),c&$6’ at* TABLE 2 Crystal data for ternary REAsPd and RESbPt alloys of the hP6 CaIng type A)
DX (g cme3)
Compound
a (+ 0.003 A)
c (t0.005
CeAsPdb PrAsPd NdAaPd
4.37 4.355 4.344
7.80 7.709 7.682
1.77 1.770 1.768
21.5 21.1 20.9
LaSbPt CeSbPt NdSbPt
4.560 4.550 4.544
8.263 8.077 7.878
1.812 1.775 1.734
24.8 24.1 23.5
c/a
8.2, 8.4s 8.6, 10.1, 10.4, 10.8,
‘Average atomic volume 7 = Vcen/6. bHeterogeneous sample.
lattice parameter variation observed (which has a very complex trend as a function of composition) suggests the existence of a certain range of solid solutions. The values of the lattice parameters are generally in the fo_llowing ranges: a = 4.68 - 4.89 A; c = 7.34 - 7.48 A; average atomic volume V = 23.3 - 25.5 A3.The homogeneity field for the 1:l:l composition extends preferentially into the samarium-rich region in a direction parallel to the CdIn axis. 3.2. REAsPd alloys The data relevant to these alloys are given in Table 2. Data for the light rare earths only are reported, since results obtained from samples prepared with the heavier rare earths could not be clearly interpreted. Generally these
LaCePr
NdPmSmEuGdTbDyHoEr
TmYb
Lu
Fig. 1. The average atomic volume of the REMeX compounds ~8. the atomic number of the rare earth: v, 0, n, $0, phases with the hP6 CaIng-type structure;A,V, O,n, phases with the cF12 MgAgAs-type structure (for the polymorphic compound HoSnAu both structural types have been identified [ 4 ] ).
samples were he~rogeneous and in their powder photo~aphs only the caption lines of the binary REAs compound were identified. 3.3. RESbPt alloys In Fig. 1 data are plotted both for the compounds prepared with the light rare earths (of the CaIns type) and for the compounds with the heavy rare earths (which have the MgAgAs-type structure [6] ). During this work the SmSbPt compound was also prepared: it had the cF12 MgAgAs-type structure with a = 6.554 A. The volume variation that we observe in the RESbPt series, on passing from the CaIna-type phases to those having the MgAgAs-type structure, may be usefully compared with the analogous trend shown by the RESbPd and RESnAu alloys (both corresponding to a nominal valence electron concentration of 8f3). In these series also we observe the MgAgAs-type structure for the compounds of the heavy rare earths and the
P5
CaIn&ype structure for the lighter rare earths. The possible reasons for the preferential stability of the less dense MgAgAs-type structure with the rare earths having smaller atomic dimensions have been discussed previously [4,
51. References 1 A. Iandelli, 2. Anorg. Chem., 330 (1964) 121. 2 P. Eckerlin and H. Kandler (eds.), Landolt-Biirnstein, Zahlenwerte und Funktionen aus Naturwissenschaften und Technik, Group III, Vol. 6, Structurdaten der Elemente und intermetallische Phasen, Springer, Berlin, 1971. 3 A. E. Dwight, Winter Meeting of the American Crystallographic Association, Columbia, 19 71, personal communication. 4 A. E. Dwight, in C. E. Lundin (ea.), Proc. 12th Rare Earth Research Conf., Vail, Colomdo, July 18 - 22, 1976, Denver Research Institute, pp. 480 - 489. 5 R. Marazza, D. Rossi and R. Ferro, J. Less-Common Met., 75 (1980) P25. 6 A. E. Dwight, in J. M. Haschke and H. Eick (eds.), Proc. 1 lth Rare Earth Research Conf., Traverse City, Michigan, October 7 - 10, 1974, Vol. 2, p. 642 7 R. Marazza, D. Rossi and R. Ferro, Gazz. Chim. Ital., 110 (1980) 357.