Handbook on the Physics and Chemistry of Rare Earths
volume 7
Elsevier, 1984
Edited by: Karl A. Gschneidner, Jr. and LeRoy Eyring ISBN: 978-0-444-86851-0
by kmno4
C O N T E N T S
Preface v C o n t e n t s vii
Contents of volumes 1 - 6 ix 51. P. Rogl
Phase equilibria in ternary and higher order systems with rare earth elements and silicon 1
52 K.H.J. Buschow Amorphous alloys 265 53 H. Schumann and W. G e n t h e
Organometallic Compounds of the rare earths 446 Subject index 573
vii
C O N T E N T S O F V O L U M E S 1 - 6
V O L U M E 1: M E T A L S
1. Z.B. Goldschmidt, Atomic properties" (free atom) 1
2. B.J. Beaudry and K.A. Gschneidner, Jr., Preparation and basic properties of the rare earth metals ,173
3. S.H. Liu, Electronic structure of rare earth metals 233 4. D.C. Koskenmaki and K.A. Gschneidner, Jr., Cerium 337
5. LJ. Sundstr/Sm, Low temperature heat capacity of the rare earth metals" 379 6. K.A. McEwen, Magnetic and transport properties of the rare earths 411
7. S.K. Sinha, Magnetic structures and inelastic neutron scattering: metals, alloys and compounds 489 8. T.E. Scott, Elastic and mechanicalproperties 591
9. A. Jayaraman, High pressure studies." metals, alloys and compounds" 707 10. C. Probst and J. Wittig, Superconductivity: metals; alloys" and compounds 749 11. M.B. Maple, L.E. DeLong and B.C. Sales, Kondo effect." alloys and compounds 797 12. M.P. Dariel, Diffusion in rare earth metals 847
Subject index 877
V O L U M E 2: A L L O Y S A N D I N T E R M E T A L L I C S
13. A. tandelli and A. Palenzona, Crystal chemistry of intermetallic compounds 1
14. H.R. Kirchmayr and C.A. Poldy, Magnetic properties of intermetallic compounds of rare earth metals 55
15. A.E. Clark, Magnetostrictive RFe 2 intermetallic compounds" 231 16. J.J. Rhyne, Amorphous' magnetic rare earth alloys 259 17. P. Fulde, Crystalfields 295
18. R.G. Barnes, N M R , E P R and Mg)ssbauer effect: metals, alloys and compounds" 387 19. P. Wachter, Europium chalcogenides: EuO, EuS, EuSe and EuTe 507
20. A. Jayaraman, Valence changes in compounds 575 Subject index 613
V O L U M E 3: N O N - M E T A L L I C C O M P O U N D S - I
21. L.A. Haskin and T.P. Paster, Geochemistry and mineralogy of the rare earths 1 22. J.E. Powell, Separation chemistly 81
23. C.K. Jorgensen, Theoretical chemistry of rare earths 111
24. W.T. Carnall, The absorption and fluorescence spectra of rare earth ions in solution 25. L.C. Thompson, Complexes 209
26. G.G. Libowitz and A.J. Maeland, Hydrides' 299 27. L. Eyring, The binary rare earth oxides" 337
28. D J . M . Bevan and E. Summerville, Mixed rare earth oxides" 401 29. C.P. Khattak and F.F.Y. Wang, Perovskites and.garnets 525
30. L.H. Brixner, J.R. Barkley and W. Jeitschko, Rare earth molybdates (VI) 609 Subject index 655
171
x C O N T E N T S OF VOLUMES 1 6 V O L U M E 4: N O N - M E T A L L I C C O M P O U N D S - II 31. J. Flahaut, Sulfides, selenides and tellurides 1
32. J.M. Haschke, Halides 89
33. F. Hulliger, Rare earth pnictides 153
34. G. Blasse, Chemistry and physies of R-activated phosphors" 237 35. M.J. Weber, Rare earth lasers 275
36. F.K. Fong, Nonradiative processes of rare-earth ions in crystals" 317
37A. J.W. O'Laughlin, Chemical spectrophotometric and polarographie methods" 341
37B. S.R. Taylor, Trace element analysis of rare earth elements by spark source mass spectrometry 359 37C. R.J. Conzemius, Analysis of rare earth matrices by spark source mass spectrometry 377
37D. E.L. DeKalb and V.A. Fassel, Optical atomic emission and absorption methods" 405 37E. A.P. D'Silva and V.A. Fassel, X-ray excited optical luminescence of the rare earths 441 37F. F. W.V. Boynton, Neutron activation analysis 457
37G. S. Schuhmann and J.A. Philpotts, Mass-spectrometric stable4sotope dilution analysis" for lanthanides in geochemical materials 471
38. J. Reuben and G.A. Elgavish, Shift reagents and N M R of paramagnetic lanthanide complexes" 483 39. J. Reuben, Bioinorganic chemistry: lanthanides as probes" in systems of biological interest 515 40. T.J. Haley, Toxocity 553
Subject index 587
V O L U M E 5
41. M. Gasgnier, Rare earth alloys and compounds as thin films 1
42. E. Gratz and M.J. Zuckermann, Transport properties" (electrical resistivity, thermoelectric' power and thermal conductivity) of rare earth intermetallic compounds 117
43. F.P. Netzer and E. Bertel, Adsorption and catalysis on rare earth surfaces" 217
44. C. Boulesteix, Defects and phase transformation near room temperature in rare earth sesquioxides 321
45. O. Greis and J.M. Haschke, Rare earth fluorides 387
46. C.A. Morrison and R.P. Leavitt, Spectroscopic properties" of triply ionized lanthanides in transparent host crystals 461
Subject index 693
V O L U M E 6
47. K.H.J. Buschow, Hydrogen absorption in intermetallic compounds' 1
48. E. Parth6 and B. Chabot, Crystal structures and crystal chemistry of ternary rare earth- transition metal borides, silicides and homologues 113
49. P. Rogl, Phase equilibria in ternary and higher order systems with rare earth elements and boron 335 50. H.B. Kagan and J.L. Namy, Preparation of divalent ytterbium and samarium derivatives' and their use
in organic chemistry 525 Subject index 567
Handbook on the Physics and Chemistry of Rare Earths, edited by K.A. Gschneidner, Jr. and L. Eyring
© Elsevier Science Publishers B. V., 1984
Chapter 51
P H A S E EQUILIBRIA IN TERNARY A N D HIGHER O R D E R S Y S T E M S W I T H RARE EARTH E L E M E N T S A N D SILICON
Peter R O G LInstitut ff~r Physikalische Chemie, Universit~t Wien, Wi~hringerstrasse 42, A-1090 Vienna, Austria
Contents I. Introduction
2. Ternary phase diagrams: rare-earth-metal-silicon
3. Multicomponent systems containing rare earth metals and silicon
2 4 246
Symbols and abbreviations a,b,c
a / o arc(Zr) CP HT(Ar) HV M E mol%
P X D QE Qu(Mo) R T~
Tm T~
To w / o PE Px
unit cell dimensions in A (for rhombohedral symmetry denoted as aR, a; for the equivalent triple-primitive hexagonal cell indicated as a n , CH)
composition in atomic percent
arc melting under Zr-gettered argon atmosphere powder mixtures were cold pressed
heat treatment under argon atmosphere high vacuum, ~ 10 4 Pa
metallographic analysis composition in molar percent powder X-ray diffraction analysis samples radiation quenched
samples wrapped in Mo foil and sealed in evacuated silica (quartz) tubes for heat treatment reliability factor of crystal structure determination defined as ]~[A F[/Y~lFobs]
superconducting transition temperature, in K magnetic ordering temperature, in K N6el temperature, in K
sample remained normal (with respect to superconductivity) down to T, in K composition in weight percent
unit cell angles in degrees (for rhombohedral symmetry denoted as a R, a) measured density ( k g / d m 3)
calculated density (kg/dm3); theoretical density, corresponding to the composition and parameters obtained from X-ray data, atomic weight based on 12C, N = 6 ~ 0 2 2 X 1 0 23 a t o m s / g m o l
2 P. ROGL 1. Introduction
The present status of information about phase equilibria and formation of ternary metal silicides with R elements (R = Sc, Y, and the lanthanides)is summarized in fig. 1. Phase equilibria have been investigated for only a small number of the possible ternary combinations R - M - S i , and for a larger number of ternary systems only a few compounds have been identified to date. Little information is available involving main group elements.
It is already some time ago that the comprehensive reviews on transition metal silicides were published by Parth6 (1970) and Nowotny (1972). Since then the production and technical application of the so-called rare earth elements has drastically increased, hand in hand with an increased scientific metallurgical interest in the R metal systems.
Most of the ternary phase diagram studies (isothermal sections) have been carried out by Gladyshevskij and coworkers at Lvov University, USSR. Only recently has the interesting interplay of superconducting and magnetic properties--first dis- covered by Matthias and coworkers in certain R - p l a t i n u m metal borides (Bell Laboratory and University of California, San Diego)--stimulated new activity in low-temperature investigations of ternary R silicides in combination with metals from the iron group. A rather comprehensive review on the electrical and magnetic properties of these materials can be found in a recent article written by Johnston and Braun (1982).
As far as the present compilation of phase diagram data of R - M - S i systems is concerned, no efforts have been made to recompile data on the binary systems i n v o l v e d - - a n d thus for details on binary systems the reader is referred to the well-known handbooks on binary phase diagrams by Hansen and Anderko (1958), Ageev (1959), Elliott (1965), Shunk (1969), Gschneidner and Verkade (1974),
~
VCe Pr
Eu Gd Tb O Ho Er Tm Yb
Fig. 1. Formation of ternary silicides and phase equilibria within ternary silicide systems: R-M Si; filled squares: complete isothermal section established; filled triangles: partial isothermal section established.
Numbers in each square correspond to the numbers of ternary silicide compounds characterized.
PHASE EQUILIBRIA 3 Eremenko et al. (1975) and Moffatt (1976). Binary phase diagrams are therefore rather briefly discussed, but it was the general intention to incorporate the most recent results and to point out those problems where further investigations will have to clarify points still in question. Critical assessments for binary R - S i or R - G e systems unfortunately are available for only a few systems and many points of uncertainty still exist. This is particularly true for the complicated polymorphic transitions of the stoichiometric and nonstoichiometric disilicides and digermanides.
The situation becomes even less transparent when one looks at the ternary solid solutions. In most cases a careful reinvestigation of the ternary phase regions containing - 60 to 70 a / o Si(Ge) over a larger temperature interval is still necessary in order to obtain more reliable phase diagram data.
]~urthermore very few reliable data exist on the ternary solubility limits as a function of temperature. The same holds for the homogeneity ranges of the ternary compounds, which have been determined with a high degree of precision in only a few cases. Therefore the small solubilities of binary and ternary compounds indi- cated ( - 0.5 a / o ) are schematic in all cases not especially specified and should serve as a guideline only.
From the various influences of the factors responsible for the stability of a crystal structure of a given composition (geometrical, electrochemical, and energy band factors), complete or extended solid solutions can be expected to form between isotypic binary silicides of the same or neighboring group numbers (see e.g. C e - Y - S i or C e - T h - S i ) . R-silicon germanides generally form extended solid solutions. The similarity in the chemical alloying behavior of the large as well as the small R members is well known. Thus in all those cases, where exact phase equilibria have not yet been derived, the known phase equilibria of one of the neighboring R elements may serve as a first order approximation. However, exchange of the second metal constituent by one of its homologous elements or even changing to a neighboring group number in general causes a considerable change in the resulting phase equilibria (compare e.g. Y - C r - S i , Y Mo-Si, Y - M n - S i , Y - R e - S i ) .
All data used in this compilation were obtained from a manual collection of the author during the past 15 years as well as from a computerized literature search consulting CAS, and M E T A D E X service up to December 31, 1983.
No attempt, however, has been made to include papers concerning the numerous technical alloys (e.g., much has been said about the production of nodular iron parts using F e - S i - R alloys), unless they revealed valuable information on phase equi- libria, solid solubilities, lattice parameters or crystal-structure data.
The "short" Hermann Mauguin symbol (according to the international Tables for X-ray Crystallography, 1974) has been used to characterize the crystal structure of each ternary c o m p o u n d in combination with its formula and name of the structure type (representative substance). Whenever information on atomic parame- ters or metal ordering--deviating from the general description of the stn~cture type c o n c e r n e d - - w a s available, it has been included; however, for a more detailed description of the crystallographic structure types, the reader is referred to the contribution by Parth6 and Chabot (1984) in vol. 6 of this Handbook, ch. 48.
Rare-earth-metal-silicon ternary phase diagrams are listed in alphabetical order
4 P. ROGL
o f t h e c h e m i c a l s y m b o l o f t h e r a r e e a r t h e l e m e n t ( C e , D r , E r , . . . , Y b ) . U n d e r e a c h r a r e e a r t h t h e s y s t e m s a r e l i s t e d a l p h a b e t i c a l l y b y t h e c h e m i c a l s y m b o l o f t h e n o n - r a r e - e a r t h e l e m e n t . A f t e r t h e t e r n a r y s y s t e m s , h i g h e r o r d e r s y s t e m s a r e p r e - s e n t e d f o l l o w i n g t h e s a m e s c h e m e .
References
Ageev, N.V., 1959, Phase Diagrams of Metallic Systems (Viniti Press, Acad. Sci. USSR, Moscow) (in Russian); regularly updated.
Elliott, R.P., 1965, Constitution of Binary Alloys, First Supplement (McGraw-Hill, New York).
Eremenko, V.N., Yu.I. Buyanov and V.G. Batalin, 1975, Phase Diagrams of Binary Systems of Germanmm with Rare Earth Metals, in: Fiz.Khim.Kondensiv.Faz. Sverkhverd.Materialov i ikh Granits Razdela (Nauka Dumka, Kiev) pp. 191-201.
Gschneidner Jr., K.A. and M.E. Verkade, 1974, Selected Cerium Phase Diagrams, Document IS-RIC-7, Rare Earth Information Center, Iowa State Univ., Ames, IA, USA.
Hansen, M. and K. Anderko, 1958, Constitution of Binary Alloys, 2nd Ed. (McGraw-Hill, New York).
Johnston, D.C. and H.F. Braun, 1982, in: Superconductivity in Ternary Compounds, eds. O. Fischer and M.B. Maple (Springer, Heidelberg).
Moffatt, W.G., 1976, The Handbook of Binary Phase Diagrams (General Electric Comp., Schenectady, NY), updating service.
Nowotny, H., 1972, in: MTP, International Review of Science, vol. 10, Inorg. Chem. Series, ed. L.E.J.
Roberts (Butterworths, New York, London).
Parth6, E., 1970, Coll. Int. CNRS 180, 61.
Parth6, E. and B. Chabot, 1984, Crystal Structures and Crystal Chemistry of Ternary Rare Earth Transi- tion Metal Borides, Silicides and Homologues, in: Handbook on the Physics and Chemistry of Rare Earths, Vol. 6, eds. K.A. Gschneidner, Jr. and L. Eyring (North-Holland, Amsterdam) p. 113.
Shunk, F.A., 1969, Constitution of Binary Alloys, Second Supplement (McGraw-Hill, New York).
2. Ternary phase diagrams: rare-earth-metal-silicon Ce-Ag-Si
F r o m X - r a y p o w d e r a n a l y s i s M a y e r e t al. ( 1 9 7 2 ) r e p o r t e d C e A g 2 S i 2 t o c r y s t a l l i z e w i t h t h e o r d e r e d T h C r 2 S i 2 - t y p e o f s t r u c t u r e [ s p a c e g r o u p I 4 / m m m ; a = 4 . 2 4 7 ( 5 ) , c = 1 0 . 6 4 ( 5 ) ] . F o r s a m p l e p r e p a r a t i o n , s e e L a A g 2 S i 2 ; t h e a l l o y s a l s o c o n t a i n e d s o m e e x c e s s A g a s w e l l as s m a l l a m o u n t s o f C e S i 2 p h a s e s ( t e t r a g o n a l a n d / o r o r t h o - r h o m b i c m o d i f i c a t i o n ? ) . F o r 29Si N M R a n d s u s c e p t i b i l i t y m e a s u r e m e n t s , s e e S a m p a t h k u m a r a n e t al. ( 1 9 7 9 ) . A f e r r i - o r f e r r o m a g n e t i c g r o u n d s t a t e w a s s u g g e s t e d f o r C e A g z S i 2 b y M u r g a i e t al. ( 1 9 8 3 ) ; T m = 8 - 1 0 K .
References
Mayer, I. and J. Cohen, 1972, J. Less-Common Metals 29, 221.
Mayer, I., J. Cohen and 1. Felner, 1973, J. Less-Common Metals 30, 181.
Murgai, V., S. Raaen, L.C. Gupta and R.D. Parks, 1982, in: Valence Instabilities, eds. P. Wachter and H.
Boppart (North-Holland, Amsterdam) p. 537.
Sampathkumaran, E.V,, L.C. Gupta and R. Vijayaraghavan, 1979, Phys. Lett. 70A(4), 356.
Ce-A l-Si
N o c o m p l e t e p h a s e d i a g r a m h a s b e e n e s t a b l i s h e d , d e s p i t e c o n s i d e r a b l e i n t e r e s t h a s b e e n d e v o t e d t o t h e t e r n a r y s y s t e m C e - A 1 - S i .
PHASE EQUILIBRIA 5
Si
400o C
# Xc si
/ " // . / y Ce3SiS)
/ . ,'~ . " l x c~si
/ 1 ~ ~ %Ces Sih
At ~-Ce3ALll \CeAL2 CeAL Ce3Ak Ce CeA/3
Si
500°C
1
. . . . . V V V
l
At oz-Ce3 ALl I CeAt2 Ce
CeA[ 3
Fig. 2. (a) Ce-A1-Si, partial isothermal section at 400 o C for 0-33 a / o Ce (after Altunina et al., 1963). 1 :
"Ce20A13sSi4s'. (b) C e - A I - S i , partial isothermal section at 500 o C for 0-33 a / o Ce (after Muravyova, 1972). 1: CeA11.25_1.75Si2.75_2.25 (earlier "Ce20A135Si45" or "CezAI3Si2"), 2: CeAlzSi2, 3:
CeA11.4_0.9Si0.6_1.1, 4: CeA11.64_1.55Si0.36_0.45.
6 P. ROGL
F r o m a rather preliminary study of the phase equilibria at 4 0 0 ° C (the Al-rich region was studied at 500°C) Zarechnyuk (1963) and Altunina et al. (1963) attempted to construct an isothermal section (see fig. 2a). Samples were prepared from 99.99% pure A1 and 99.567% pure Ce by melting in an A1203 crucible under a protective layer of a mixture of KC1 + LiC1. The alloys were annealed for 50 100 h at 400 o C, and 25 samples in the Al-rich region at 500 ° C. Phase composition was checked in some cases by chemical analysis. Phase equilibria were determined as based upon X-ray powder and metallographic analyses. Etching was possible in mixtures of HNO3, H F and glycerin. Microhardness values were obtained at a load of 100 g.
A wide homogeneous region was found for mixed crystals CeSi 2-xAlx (c~-ThSi 2- type) extending up to 55-60 a / o A1 at 4 0 0 ° C (Si/A1 substitution), and lattice parameters were claimed to change linearly from a = 4.158, c = 13.898 (CeSi2) to a = 4.239, c = 15.231 at 60 a / o A1 (data converted from kX units). Microhardness values were H = 610 ( + 10) k g / m m 2 (at 2 w / o A1)', and H = 460 ( + 10) k g / m m 2 at 20 w / o A1.
The solid solubility of Ce and Si in AI has been studied at 500 ° C and the variations of the lattice parameters were recorded along two concentration lines at 95 w / o A1 and at 98 a / o A1, respectively.
At a composition (in a / o ) Ce20A135Si45 a ternary c o m p o u n d was observed, which tentatively was indexed hexagonal with c / a ~ 1.17; H = 290 ( + 10) k g / m m 2. The ternary phase was suspected to correspond to the c o m p o u n d "Ce2A13Sia" men- tioned by Brauer and Haag (1952), who obtained this phase in an unsuccessful attempt to prepare CeSi 2 by reaction of a C e A 1 9 melt with excess Si at 900 ° C in an A1203 crucible under a protective layer of NaC1. After 1 h at 900 ° C and subsequent cooling to 600 o C in 2.5 h the obtained alloy was boiled in 2n-NaOH. The remainder was of metallic luster and well crystallized. Indexing was possible on the basis of a hexagonal cell a = 6.242, c = 7.304 (converted from kX units).
At variance with the results of Altunina et al. (1963) concerning the wide homogeneous range of CeSi 2 xAlx, Raman (1967) and R a m a n and Steinfink (1967) reported the existence of a ternary AiB2-type of structure in a ternary alloy CeAll.625Si0.375 annealed at 1000°C [ P 6 / m m m , a = 4.315(5) and c = 4.298(5)].
Muravyova et al. (1972) prepared and characterized the compound CeA12Si2, which was found to crystallize with the La2OzS-type of structure with the space group P3ml and lattice parameters a = 4.21 and c = 6.94; powder intensities were calculated on the basis o f the atom parameters as derived for the isotypic CaA12Si 2 (for details, see Sm-A1-Si), and correspondance to the observed intensity data was said to be satisfactory.
Muravyova (1972) reinvestigated the phase equilibria for the 0 - 3 3 a / o Ce section (see fig. 2b) of the C e - A 1 - S i system by means of X-ray powder and metallographic analysis of 65 alloys which were arc-melted and subsequently annealed for 150-750 h at 5 0 0 ° C in evacuated silica tubes. The starting materials were 99.0% Ce and 99.90% A1, Si.
F r o m a recent compilation of Ce phase diagram data, the binary Ce-A1 system at 400-500 ° C comprises five intermetallic phases: /3-Ce3A1 , CeA1, CeA12, CeA13, and
PHASE EQUILIBRIA 7 c~-Ce3Alll (Gschneidner and Verkade, 1974). Only two Ce aluminides were shown by Altunina et al. (1963): CeA12(MgCu2-type ) and "CeA14" (now c~-Ce3A121 with a BaA14-derivative type). Similarly only CeSi 2 (c~-ThSi2-type) was reported for the Ce-Si binary. The solid solubility of Si in c~-Ce3Alll (given as "CeAI4"), in CeA13 and in CeA12 was observed to be rather small ( ~ 1 a / o Ce). Raman and Steinfink (1967) observed an alloy CeAla.94Si0.06 annealed at 1 0 0 0 ° C to be single phase MgCu2-type with a = 8.040(5) suggesting a solid solubility of ~ 2 a / o Si in CeA12 (MgCuz-type) at 1000°C. The solid solubility of A1 in CeSi 2 was given by Mura- vyova (1972) to be - 5 at% A1 at 500°C, but according to the powder X-ray data of Raman and Steinfink (1967) the solubility of A1 in CeSi 2 with a-ThSi 2 type at 1000 ° C at least was found to extend to CeA1].sSi0. 5 [a = 4.280(5), c = 14.90(1)]; for details of sample preparation, see N d - A 1 - S i .
Four ternary compounds were observed confirming the earlier findings concern- ing the compounds CeAl i. 25-1.75 Si 2.75 - 2.25 (earlier" Ce20 A135 Si 45", Zarechnyuk, 1963;
Altunina et al., 1963; and "CezA13Si2", Brauer and Haag, 1952) and CeA12Si2, Muravyova et al. (1972). The compound Cel.64_1.55Si0.36_0.45 with the A1B2-type and a considerable homogeneity region ranging from a := 4.35, c = 4.30 to a = 4.32, c = 4.43 reveals slightly larger unit cell dimensions than those obtained by Raman (1967) for CeA11.625Si0.375 at 1000 ° C.
CeAll.4_0,9Si0.6_1.1 was said to crystallize with the a-ThSi 2 type (i4~/amd, a = 4.25-4.27, c = 14.54-14.92); the atom parameters were 4 Ce in 4a) 0, 0, 0 and a statistical occupation of 4 A1 + 4 Si in 8e) 0, 0, 0.417. Around the composition CeA1Si ordering among A1 and Si atoms in terms of a LaPtSi-type (a-ThSi2-deriva- tive type) seems likely.
N o c o m p l e t e s t r u c t u r e d e t e r m i n a t i o n has b e e n carried o u t for CeAll.25_1.75Si2.75_2.25, but from a preliminary analysis of single crystal X-ray photographs, Muravyova (1972) was able to propose a trigonal symmetry corre- sponding to the possible space groups R3m, R32 or R3m; lattice parameters for an alloy CeAll.25Si2.75 were a = 3.85, c = 9.47.
R@rences
Altunina, L.N., E.I. Gladyshevskij, O.S. Zarechnyuk and I.F. Kolobnev, 1963, Zh. Neorg. Khim. 8(7), 1673.
Brauer, G. and H. Haag, 1952, Z. Anorg. Allg. Chem. 267, 198.
Gschneidner Jr., K.A. and M.E. Verkade, 1974, Selected Cerium Phase Diagrams, Document IS-RIC-7, Iowa State Univ., Ames, IA, USA, p. 36.
Muravyova, A.A., 1972, Autoreferat Dis. Kand. Khim. (abstract of thesis, Russian) (Nauk, Lvov) 18 p.
Muravyova, A.A., O.S. Zarechnyuk and E.I. Gladyshevskij, 1972, Visn. L'vivsk. Univ., Ser. Khim. 13, 14.
Raman, A., 1967, Z. Metallkde 58(3), 179.
Raman, A. and H. Steinfink, 1967, Inorg. Chem. 6(10), 1789.
Zarechnyuk, O.S., 1963, Zb. Robit Aspirantiv, L'vivsk. Univ., Prirodn. (Nauk, Lvov) pp. 15-20.
C e - A u - S i
F r o m X-ray powder analysis Mayer et al. (1973) reported CeAu2Si 2 to crystallize with the ordered ThCr2Si2-type of structure: I 4 / m m m , a---4.326(5), c = 10.24(5).
For sample preparation, see LaAu 2 Si 2. Antiferromagnetic ordering was observed by
8 P. R O G L
F e l n e r (1975) at T N = 6.6 K a n d b y M u r g a i et al. (1983) at T N = 8 10 K ( m a g n e t i c s u s c e p t i b i l i t y and electrical resistivity m e a s u r e m e n t s in the t e m p e r a t u r e r a n g e 1.5 <
T < 300 K a n d high field m a g n e t i z a t i o n studies at 4.2 K up to 21 T). T h e p a r a m a g n e t i c b e h a v i o r is c h a r a c t e r i z e d b y /Zcf f = 2.3 /~B a n d 0p = --2.8 K ( F e l n e r , para 1975). F o r 29Si N M R a n d s u s c e p t i b i l i t y m e a s u r e m e n t s , see S a m p a t h k u m a r a n et al.
(1979).
References
Felner, I., 1975, J. Phys. Chem. Sol. 36, 1063.
Mayer, I., J. Cohen and I. Felner, 1973, J. L e s s - C o m m o n Metals 30, 181.
Murgai, V., S. Raaen, L.C. G u p t a and R.D. Parks, 1983, private communication.
S a m p a t h k u m a r a n , E.V., L.C. G u p t a and R. Vijayaraghavan, 1979, Phys. Lett. 70A(4), 356.
C e - C o - Si
By m e a n s of X - r a y p o w d e r a n d m e t a l l o g r a p h i c analysis of 160 a r c - m e l t e d alloys B o d a k a n d G l a d y s h e v s k i j (1970) e s t a b l i s h e d two p a r t i a l i s o t h e r m a l sections of the s y s t e m C e - C o - S i at 8 0 0 ° C ( r e g i o n 0 - 3 3 a / o Ce) a n d at 4 0 0 ° C for the r e g i o n 3 3 - 1 0 0 a / o Ce. T h e a l l o y b u t t o n s were h e a t - t r e a t e d for 250 h at 800 o C, a n d 500 h at 4 0 0 ° C , respectively. S t a r t i n g m a t e r i a l s were p o w d e r s of Ce 99.56%, C o 99.87%
a n d Si 99.99%. E t c h i n g was p o s s i b l e in a q u e o u s s o l u t i o n s of H F , H N O 3 a n d glycerin. M i c r o h a r d n e s s values were d e t e r m i n e d at a l o a d o f 50 100 g.
Si
800 °C ,~
CoSi2 , ~ -711 ~ C e Si2
~. / / ~ / / 51~./ff-.~..~\CeSi
C O ~ Ce5 Si~
400 °C
Co Ce2Cd17/\~CeCo2 Ce2~Co n Ce
I ~
CeCo 5 Ce2Co / CeCo3
Gel5 Co 19
Fig. 3. C e - C o - S i , partial isothermal sections at 800 o C ( 0 - 3 3 a / o Ce) and at 400 o C (33-100 a / o Ce). 1 : Ce3CosSi , .2: CeCo8.8_8.4Si4.2_4.6, 3: CeCoSi, 4: CeCozSi 2, 5: CeCoSi 2, 6: CeCo0.5_0.3Sil.5_1. 7, 7:
CeCoSi3; the location of a high-temperature phase (?) Ce2Co3Si 5 is marked by an asterisk.
PHASE E Q U I L I B R I A 9 The s o l i d s o l u b i l i t y o f Si in C o ( - 13 a / o at 8 0 0 ° C ) as well as the b i n a r y c o b a l t silicides are in a g r e e m e n t with the d a t a in h a n d b o o k s o f b i n a r y p h a s e d i a g r a m s [Co2Si (Co2Si-type), C o S i (FeSi-type), C o S i 2 (CaF2-type)]. F o r Ce silicides, see the C e - N i - S i system. T h e c o m p o u n d Ce3Si 5 was n o t o b s e r v e d b y B o d a k a n d G l a d y s h e v s k i j (1970); its position, however, is m a r k e d in fig. 3 b y a b l a c k circle. T h e b i n a r y s y s t e m C e - C o b a s i c a l l y agrees with a r e c e n t c o m p i l a t i o n of p h a s e d i a g r a m d a t a b y G s c h n e i d n e r a n d V e r k a d e (1974) a n d I a n d e l l i a n d P a l e n z o n a (1979).
Ce5Cot9 w i t h a new s t r u c t u r e t y p e will have to b e i n c l u d e d . D u e to its r e d u c e d s t a b i l i t y w i t h r e s p e c t to its n e i g h b o r i n g p h a s e s C e C % a n d Ce2C07, a r a t h e r l i m i t e d solid s o l u b i l i t y of Si in Ce5Co19 is likely, which in t u r n w o u l d result in the f o r m a t i o n o f a t h r e e - p h a s e e q u i l i b r i u m : C e s ( C o , S i ) l 9 + Ce(Co,Si)5 + Ce2(Co,Si)l 7. M u t u a l solid solubilities of the b i n a r y c o m p o u n d s were o b s e r v e d to b e small; C o silicides d o n o t dissolve Ce, w h e r e a s Ce2Co17 dissolves u p to 10 a / o Si a n d C e C % dissolves up to 14 a / o Si. L a t t i c e p a r a m e t e r s , as r e a d f r o m a small d i a g r a m , c h a n g e f r o m a = 8.38, c = 8.13 (Ce2Col7) to a = 8.32, c = 8.15 for Ce2(Co,Si)17, a n d f r o m a = 4.90, c = 4.035 ( C e C % ) to a = 4.835, c = 4.050 for Ce(Co,Si)5. Seven t e r n a r y c o m p o u n d s were observed, w h i c h all h a d v a r i a b l e Co,Si c o n t e n t at a fixed Ce c o n c e n t r a t i o n .
In an e a r l y s t u d y o f p h a s e e q u i l i b r i a w i t h i n the C e - p o o r region, B o d a k a n d G l a d y s h e v s k i j (1969) o b s e r v e d a t e r n a r y c o m p o u n d CeCo88_84Si4. 2 4.6 w i t h a te- t r a g o n a l N a Z n 1 3 - d e r i v a t i v e t y p e [lattice p a r a m e t e r s first were given as a 0 = 11.01(1) a n d c o = 11.53(1)]. A m o r e correct c r y s t a l l o g r a p h i c d e s c r i p t i o n o f this p h a s e as an i s o t y p i c r e p r e s e n t a t i v e o f the s t r u c t u r e t y p e o f Ce2Ni17Si 9 was l a t e r given b y B o d a k a n d G l a d y s h e v s k i j (1970): a = 7.79
( a = a o / V ~ ) , c=
11.53 a n d the space g r o u p I 4 / m c m . T h e m i c r o h a r d n e s s at a l o a d of 50 o r 100 g was r e p o r t e d to be H = 681 ( _+ 50) k g / m m 2.A n e x t e n d e d h o m o g e n e i t y range was o b s e r v e d b y B o d a k a n d G l a d y s h e v s k i j (1970) for the A1B2-type p h a s e CeCoo.5_03Sia. 5 1.7 w i t h s p a c e g r o u p P 6 / m m m . L a t t i c e p a r a m e t e r s r a n g e f r o m a = 4.044, c = 4.194 at 50 a / o Si ( m i c r o h a r d n e s s 613 + 50 k g / m m 2) to a = 4.025 a n d c = 4.29 at 54 a / o Si. G l a d y s k e v s i j a n d B o d a k (1965) g a v e slightly d i f f e r e n t p a r a m e t e r s for Ce(Co,Si)2: a = 4.051, c = 4.187 (arc m e l t e d , 8 0 0 ° C , 100 h). I n a g r e e m e n t w i t h this M a y e r a n d T a s s a (1969) r e p o r t e d , f r o m a p h a s e e q u i l i b r i a s t u d y of the section CeCoxSi 2 .~ at 700 8 0 0 ° C , the existence o f an A1B2-type s t r u c t u r e at the c o m p o s i t i o n CeCo0.4Sil. 6 ( P 6 / m m m , a = 4.046, c = 4 . 2 6 6 ) . I n similarity to the X - r a y p o w d e r d a t a o f NdFe0.4Sil. 6 a s t a t i s t i c a l d i s t r i b u t i o n of Si,Co a t o m s in the 2d sites was a s s u m e d . F o r x < 0.4 the T h S i 2 - t y p e was said to b e stable, a n d for x > 0.4 X - r a y p o w d e r p a t t e r n s were c l a i m e d to b e " c o m p l i c a t e d " . F o r s a m p l e p r e p a r a t i o n , see GdCo0.4Sil. 6. F r o m s u s c e p t i b i l i t y m e a s u r e m e n t s of CeCo0.4Sil. 6 (4.2 to 300 K), F e l n e r a n d Schieber (1973) d e r i v e d para /~o~f = 4 . 9 / ~ B a n d 0 p = - 9 K .
C e C o S i is t e t r a g o n a l w i t h the P b F C l - t y p e of s t r u c t u r e : a = 4.066(3), c = 6.965(5), P 4 / n m m ( X - r a y p o w d e r analysis; B o d a k et al., 1970). for a t o m p a r a m e t e r s a n d s a m p l e p r e p a r a t i o n , see C e F e S i . B o d a k a n d G l a d y s h e v s k i j (1970) r e p o r t e d a = 4.040 a n d c = 6.979; the m i c r o h a r d n e s s was H = 166 ( + 50) k g / m m 2.
CeCo2Si 2 crystallizes w i t h the o r d e r e d T h C r 2 S i 2 - t y p e o f s t r u c t u r e : s p a c e g r o u p I 4 / m l m n , a = 3.962(6), c = 9.795(10), Px = 6.78 k g / d m 3 ( R i e g e r a n d Parth6, 1969;
10 P. R O G L
X - r a y p o w d e r analysis). S a m p l e s were a r c - m e l t e d a n d h e a t - t r e a t e d in e v a c u a t e d silica t u b e s at 900 ° C for 100 h. B a n a n d S i k i r i c a (1965) r e p o r t e d a = 3.957(10) a n d c = 9.783(10) f r o m X - r a y p o w d e r a n a l y s i s of a r c - m e l t e d s a m p l e s (Ce 99.56%, C o 99.8%, Si 99.99%). B o d a k a n d G l a y s h e v s k i j (1970) c o n f i r m e d the s t r u c t u r e ( a = 3.962, c = 9.809) a n d m e a s u r e d the m i c r o h a r d n e s s H = 824 (_+ 50) k g / m m 2.
C e C o S i 3 was first c l a i m e d b y B o d a k a n d G l a d y s h e v s k i j (1970) to c r y s t a l l i z e in a n e w s u p e r s t r u c t u r e of the B a A l 4 - t y p e w i t h a c r y s t a l s y m m e t r y I 4 / m m m a n d l a t t i c e p a r a m e t e r s a = 4.14, c = 9.50. T h e m i c r o h a r d n e s s was given as 498 (_+ 50) k g / m m 2.
M o r e r e c e n t l y C h a b o t (1983) e s t a b l i s h e d , f r o m X - r a y p o w d e r data, the c o r r e c t s y m m e t r y a n d a t o m o r d e r to b e i s o s t r u c t u r a l with the B a N i S n 3 - t y p e , I 4 m m , a = 4.1344(8) a n d c = 9.561(3).
C e C o S i 2 is i s o t y p i c with the c r y s t a l s t r u c t u r e of C e N i S i 2 : C m c m , a = 4.093(2), b = 16.397(8), c = 4.036(2); Pexp = 6.15, iOtheor = 6.219 k g / d m 3 ; m i c r o h a r d n e s s H = 311 (+_50) k g / m m 2 ( B o d a k a n d G l a d y s h e v s k i j , 1970). A t o m p a r a m e t e r s were r e f i n e d b y Lukasziewicz a n d B o d a k (1969) f r o m single c r y s t a l X - r a y p h o t o g r a p h s : all a t o m s were f o u n d to o c c u p y the 4c) sites (0, y,0) of C m c m : Ce, y = 0.1074(4); Co, y = 0.3180(11); Si, y = 0.4588(15) a n d Si, y = 0.7482(21); R = 0.171. Single c r y s t a l s w e r e d i r e c t l y o b t a i n e d f r o m an a r c - m e l t e d a l l o y of c o m p o s i t i o n C e C o S i 2 , b y slowly c o o l i n g the melt. Pelizzone et al. (1982) c o n f i r m e d the s t r u c t u r e t y p e a n d gave a = 4.094(2), b = 16.440(7), c = 4.043(2). F o r m a g n e t i c d a t a , see below.
Ce3CosSi crystallizes with the o r d e r e d C e N i 3 ( s u p e r - ) s t r u c t u r e : P 6 3 / m m c , a = 4.960(1), c = 16.450(10), Pexp = 8 . 4 5 , Px = 8.65 k g / d m 3. T h e a t o m o r d e r was de- t e r m i n e d b y B o d a k (1971) b y X - r a y p o w d e r m e t h o d s : Ce in 2c) a n d 4f); C o in 12k), 2b), 2d), a n d Si in 2a); the r e l i a b i l i t y f a c t o r was R = 0.144. B o d a k a n d G l a d y s h e v s k i j (1970) r e p o r t e d a m i c r o h a r d n e s s of 613 (+_ 50) k g / m m 2, b u t slightly d i f f e r e n t l a t t i c e p a r a m e t e r s a = 4.95 a n d c = 16.25.
C h a b o t a n d Parth6 (1984) o b s e r v e d the existence of a c o m p o u n d Ce2Co3Si 5 in a r c - m e l t e d alloys w h i c h s u b s e q u e n t l y were s e a l e d in q u a r t z t u b e s a n d h e a t - t r e a t e d at l l 0 0 ° C for 24 h a n d a d d i t i o n a l l y at 1 0 0 0 ° C for 150 h. Ce2Co3Si 5 a d o p t s the U2Co3Sis-type of s t r u c t u r e w i t h s p a c e g r o u p I b a m a n d l a t t i c e p a r a m e t e r s as follows:
a = 9.623(3), b = 11.306(3) a n d c = 5.652(2).
M a g n e t i c s u s c e p t i b i l i t y d a t a o b t a i n e d f r o m a t e m p e r a t u r e r a n g e of 7 7 - 3 0 0 K w e r e p r e s e n t e d b y B o d a k et al. (1977) for CeCo0.sSil.5 (A1B2-type, /.Lef para t : 3.3 / ~ , 0 p = - 4 0 0 K); C e C o S i ( P b F C l - t y p e , ~eff"para:3"6 ~I3, 0 p = - - 1 1 0 K); C e C o S i 3 (BaA14-derivative type, X~ = 5.14 × 10 - 6 c m 3 g - 1 ) a n d CeCo2Si 2 ( T h C r 2 S i 2 - t y p e , /~p~ra = 3.16 eff ~ B ' 0p : - - 1 9 0 K). F o r b a n d - s t r u c t u r e c a l c u l a t i o n s a n d p h y s i c a l p r o p e r - ties o f CeCo2Si2, see K o t e r l i n (1981), K o t e r l i n et al. (1981), Levin (1979) a n d L e v i n et al. (1981). T h e m a g n e t i c d a t a for C e C o S i 2 ( C e N i S i 2 - t y p e , t~P~ ra = 1 . 6 / ~ , 0p = - 240 K ) as p r e s e n t e d b y B o d a k et al. (1977) d o not, however, c o r r e s p o n d to the values r e c e n t l y p u b l i s h e d b y Pelizzone et al. (1982), w h o o b s e r v e d at T > 70 K a t e m p e r a - t u r e - i n d e p e n d e n t p a r a m a g n e t i s m , suggesting Ce in a t e t r a v a l e n t state a c c o r d i n g to its s m a l l e r lattice p a r a m e t e r s as c o m p a r e d w i t h the i s o t y p i c R C o S i 2 series o f c o m p o u n d s .
P H A S E E Q U I L I B R I A 11
_References
Ban, Z. and M. Sikirica, 1965, Acta Crystallogr. 18, 594.
Bodak, O.1., 1971, Visn. L'vivsk. Derzh. Univ., Ser. Khim. 12, 22.
Bodak, O.1. and E.I. Gladyshevskij, 1969, Dopov. Akad. Nauk. Ukr. RSR, Ser. A 12, 1125.
Bodak, O.1. and E.I. Gladyshevskij, 1970, Izv. Akad. N a u k SSSR, Neorg. Mater. 6(6), 1186.
Bodak, O.I., E.L Gladyshevskij and P.I. Kripyakevich, 1970, Zh. Strukt. Khim. 11(2), 305.
Bodak, O.I., E.I. Gladyshevskij, E.M. Levin and R.V. Lutsiv, 1977, Dopov. Akad. N a u k Ukr. RSR., Ser.
A 12, 1129.
Chabot, B., 1983, unpublished results.
Chahot, B. and E. Parth6, 1984, J. Less-Common Metals 97, 285.
Felner, I. and M. Schieber, 1973, Solid State Commun. 13, 457.
Gladyshevskij, E.1. and O.I. Bodak, 1965, Dopov. Akad. N a u k Ukr. RSR., Ser. A 5, 601.
Gschneidner Jr., K.A. and M.E. Verkade, 1974, Selected Cerium Phase Diagrams Document IS-RIC-7, Iowa State Univ., Ames, IA, USA, p. 14.
Iandelli, A. and A. Palenzona, 1979, Crystal Chemistry of Intermetallic Compounds, in: Handbook on the Physics and Chemistry of Rare Earths, Vol. 2, eds. K.A. Gschneidner, Jr. and L. Eyring (North-Hol- land, Amsterdam) p. 1.
Koterlin, M.P., 1981, Dopov. Akad. Nauk Ukr. RSR., Ser. A 5, 71.
Koterlin, M.P., E.M. Levin and R.I. Yasnitskii, 1981, Ukr. Fiz. Zh. 26(11), 1917.
Levin, E.M., 1979, Ukr. Fiz. Zh. 24(9), 1386.
Levin, E.M., R.V. Lutsiv, L.D. Finkelstein, N.D. Samsonova and R.I. Yasnitskii, 1981, Fiz. Tverd. Tela 23(8), 2401.
Lukaszewicz, K. and O. Bodak, 1969, Bull. Acad. Polon. Sci., Ser. Sci. Chim. XVII(2), 63.
Mayer, I. and M. Tassa, 1969, J. Less-Common Metals 19, 173.
Pelizzone, M., H.F. Braun and J. MiJller, 1982, J. Magn. Magn. Mater. 30, 33.
Rieger, W. and E. Parth6, 1969, Monatsh. Chem. 100, 444.
C e - C u Si
Bodak et al. (1974) investigated the phase equilibria of the system Ce Cu Si and produced two partial isothermal sections, at 6 0 0 ° C (region 0 - 3 3 a / o Ce) and at 4 0 0 ° C ( 3 3 - 1 0 0 a / o Ce). The phase equilibria were determined by means of metallographic and X-ray analysis of 160 alloys, prepared by arc melting under argon from 99.4% pure Ce, 99.93% pure Cu and 99.99% pure Si. N o details were reported concerning the circumstances of the annealing technique (150 h at 600 °C;
250 h at 4 0 0 ° C ) . Chemical analysis--performed in s o m e c a s e s - - c o n f i r m e d the correspondence between nominal and actual composition within 1%. Etching was possible by a mixture of HF, H N O 3 and glycerin; microhardness was measured at a load of 100 g, and pycnometric densities were measured in kerosene.
The C e - C u binary system corresponds to a recent critical assessment of phase diagram data by Gschneidner and Verkade (1974) [CeCu 6 (CeCu6-type), CeCu5 (CaCu 5-type), CeCu 4 (CeCu 4-type ?), CeCu z (CeCu z-type) and CeCu (CsCl-type)].
The copper silicides, as recorded in fig. 4, were identified according to the system adopted by Hansen and Anderko (1958) [c~ is the solid solubility of Si in Cu ( - 10 a / o at 6 0 0 ° C ) ; K (Mg-type), y (/3-Mn-type), c (CulsSia-type), ~/, 7/ are crystallo- graphic modifications of Ca3Si ]. The binary Ce silicides have been discussed in combination with the system C e - N i - S i . "C% Si 5'' (its location in fig. 4 is marked by a black circle) was not observed by Bodak et al. (1974). The two disilicide modifications with 1-GdSi z and h-ThSiz-type were both reported at the ideal concentration of CeSi) with a solid state transformation at 1000 ° C. Solid solubility
12 P. R O G L
Si
S'2
( ~ ~ ~,'
CU CeCuslCeCu4 CeCu 2 CeCu Ce
CeCus
Fig. 4. Ce C u - S i , partial isothermal sections at 600 o C (0 33 a / o Ce) and at 400 o C (33-100 a / o Ce). l : CeCul.19_l.10Si0.81_0.90, 2: CeCul.6Sil.4, 3: CeCu2Si2, 4:CeCn0.76_0.448il.24_l.56 , 5: CeCuSi 2.
of Ce in copper silicides was said to be negligible (no details given) and mutual solid solubilities of binary C e - C u and C e - S i compounds as well as the ternary homoge- neous regions were found to extend at a fixed Ce concentration with C u / S i substitution. Solubilities in general are less than 5 a / o Cu(Si). 7 a / o Cu was observed to dissolve in CeSi 2 (see also fig. 5 for the volume change), and - 9 a / o Cu dissolved in Ce 5 Si 3. Similarly - 9 a / o Cu can be replaced by Si in CeCu 5.
Five ternary compounds were identified confirming earlier results about the existence of C e C u z S i 2 (Bodak et al., 1966; Rieger and Parth6, 1969b), and the existence of phases with A1B:-type (Gladyshevskij and Bodak, 1965; Raman, 1967;
Rieger and Parth6, 1969a).
CeCuzSi 2 crystallizes with the ThCr2Si2-type of structure: I 4 / m m m , a = 4.103(10), c = 9.986(10) (powder X-ray data, Bodak et al., 1966). Rieger and Parth6 (1969b) reported smaller unit cell dimensions from an alloy annealed at 9 0 0 ° C [a = 4.105(6), c = 9.933(10)] eventually indicating a wider homogeneous range at higher temperatures? For sample preparation, see (Y,La)CuzSi 2. Electric conductiv- ity was measured by Bodak and Gladyshevskij (1970) (o = 7800 ~2 1 cm-1), and microhardness was H = 394(50) k g / m m 3 (Bodak et al., 1974). CeCu2Si 2 is para-~
magnetic above 4.2 K. Among the mixed valence compounds CeCu2Si 2 so far is the only case for the possible existence of superconductivity (see Steglich et al., 1979 and Aliev et al., 1982, 1983). For a comprehensive review on the physical properties, see the papers of Sales and Viswanathan (1976), Sampathkumaran et al., (1979), Levin et al. (1981), Stewart et al. (1983) and Padalia et al. (1983); the anomalous
P H A S E E Q U I L I B R I A 13
t
z) ._1 o
t
2]
20
CeCu 0 . 7 6 - 0 . 4 4
Sil,24-1.56
0.90
l IIP
40
60CeSi 2
ATOM °/o Si ~- c" i ~--'O--°- --
CeCu i,~9-1.10 Si0.81-
19 J I~I
20 Ce Cu 2
Fig. 5. C e - C u - S i ; section CeCu2-CeSi2: volume versus concentration. After Bodak et al. (1974).
Single-phased regions are indicated by a black bar (see also fig. 4). With respect to recent data by landelli (1983) the unit cell parameters for the phase CeCul.19 1.10Si0.81 o.9o might in fact be subcell parameters according to the relation: a ( N i 2 I n ) = a(AIB2); c(Ni2In ) = 2c(AIB2).
l o w - t e m p e r a t u r e b e h a v i o r ( s u p e r c o n d u c t i v i t y at T~ = 0.55(15) K ) is r e v i e w e d b y L i e k e et al. (1982) a n d b y Bredl et al. (1983) (gap-less s u p e r c o n d u c t i v i t y ) . F o r 298i N M R r e s o n a n c e a n d r e l a x a t i o n studies, see A a r t s et al. (1983). I s h i k a w a et al. (1983) i n v e s t i g a t e d the effect of c o m p o s i t i o n on the s u p e r c o n d u c t i v i t y o f C e C u 2 S i 2. T h e i r l a t t i c e p a r a m e t e r s a n d s u p e r c o n d u c t i n g t r a n s i t i o n t e m p e r a t u r e s a r e listed in t a b l e 1.
F u r t h e r m o r e , f r o m D T A e x p e r i m e n t s C e C u z S i 2 was r e p o r t e d b y I s h i k a w a et al.
(1983) to f o r m p e r i t e c t i c a l l y at 1540 + 15 o C (liquid at 1550 ° C).
F o r t r a n s p o r t p r o p e r t i e s of C e C u 2 S i 2 b e t w e e n 1.5 a n d 300 K (electrical resistiv- ity, t h e r m a l c o n d u c t i v i t y a n d t h e r m o e l e c t r i c p o w e r ) see F r a n z et al. (1978) and G s c h n e i d n e r et al. (1983). S t r u c t u r a l p r o p e r t i e s a n d b a n d s t r u c u r e are d i s c u s s e d b y J a r l b o r g et al. (1983); details of crystal g r o w t h are given b y K l e t o w s k i (1983).
T h e two t e r n a r y p h a s e s CeCul.6Sil. 4 a n d C e C u S i 2 w e r e o b s e r v e d to c r y s t a l l i z e in the s a m e s p a c e g r o u p C m c m with o c c u p a t i o n o f the s a m e c r y s t a l l o g r a p h i c sites.
H o w e v e r , a c c o r d i n g to the p h a s e e q u i l i b r i a at 600 ° C in fig. 4, these c o m p o u n d s are s e p a r a t e d b y a t w o - p h a s e field C e C u z S i 2 4 - C e C u o s S i l . s. C e C u S i 2 was said to b e i s o t y p i c w i t h the c r y s t a l s t r u c t u r e of C e N i S i 2 ( C m c m , a = 4.12, b = 16.48, c = 4.16, H = 613(50) k g / m m 2 ) . A t variance with C e C u S i 2 w i t h an o r d e r e d a t o m i c a r r a n g e - ment, the c o m p o u n d CeCul.6Sil. 4 reveals a s t a t i s t i c a l o c c u p a t i o n of C u a n d Si a t o m s in e q u i p o i n t s 4c) o f C m c m ( a = 4.16, b = 17.21, c = 4 . t 7 , X - r a y p o w d e r a n d single- c r y s t a l d a t a ; H = 464(50) k g / m m 2 ) ; Ce in 4c) 0 , y = 0.109, ¼; C u in 4c) y = 0.748 a n d C u + Si in 4c) y = 0.462; Si in 4c) y = 0.322; Pcxp = 6.41, 0x = 6.47 k g / d m 3 ; R = 0.177 ( B o d a k et al., 1971).
A s i m i l a r s i t u a t i o n was m e t for the two p h a s e s w i t h c o m p o s i t i o n s CeCul.19_HoSio ~1_o.9o ( a = 4.231--4.238, c = 3.989 4.030; H = 4 4 6 ( 5 0 ) k g / m m 2) and
14 P. ROGL TABLE 1
Superconducting transition temperatures T~ (midpoint; 10% and 90% of the transition in parentheses) and lattice parameters.
Nominal T c (K) Lattice parameters
composition 50% (90% - 10%)
a C
(X) (3,)
Cels.7Cu44Si37.3 0.63 (0.65 - 0.58) 4.1034(4) 9.925(1)
Ce19.3Cu428i38.7 0.67 (0.68 - 0.60) 4.1012(3) 9.925(1)
Ce19.7Cu41Si39.3 0.67 (0.68 - 0.60) 4.1003(3) 9.920(1)
CezoCu4oSi4o 0.54 (0.58 - 0.44) 4.1004(7) 9.925(3)
Ce2o.3Cu39Si40.7 < 0.07 4.1014(5) 9.923(1)
Ce20.7 Cu 38Si41.3 < 0.07 4.1026(8) 9.923(3)
Ce2oCu 3s.sSi41.5 < 0.07 4.1053(8) 9.934(3)
Ce2oCn39.25Si4o.75 0.22 (0.325 - 0.1) 4.1016(6) 9.924(2)
Ce2oCu39.758i4o.25 0.25 (0.325 - 0.1) 4.1010(4) 9.924(2)
Ce20Cu 40.25Si39.75 0.66 (0.675 - 0.58) 4.1017(8) 9.923(3)
Ce2oCu4o.75Si39.25 0.64 (0.675 - 0.58) 4.1010(6) 9.918(2)
Ce/oCuazsSi3v.s 0.23 (0.33 - 0.14) 4.1106(5) 9.895(2)
Ce2o.7Cu41.3Si3s 0.24 (0.39 - 0.1) 4.1132(4) 9.891(2)
Cel9.3Cu 38.7Si42 0.29 (0.37-0.1) 4.1013(4) 9.923(2)
Cel8Cu41SI41 0.13 (0.22 - 0.07) 4.1026(4) 9.924(2)
Ce22.sCn38.6Si38.6 0.45 (0.5 - 0.39) 4.1062(4) 9.911(2)
CeCuo.76-0.44Sil.24 1.56 ( a = 4 . 1 0 3 - 4 . 0 7 0 , c = 4 . 2 4 4 - 4 . 2 9 1 ; H = 634(50) k g / m m 2 ) . B o t h p h a s e s w e r e c l a i m e d to c r y s t a l l i z e w i t h t h e A1B2-type a n d b o t h c o m p o u n d s e x h i b i t a h o m o g e n e o u s r a n g e , b u t a c c o r d i n g to fig. 4 they, a r e s e p a r a t e d b y a c o m m o n t w o - p h a s e field. T h e e x i s t e n c e o f t h e w i d e - s p r e a d o c c u r r e n c e o f A1B2-type p h a s e s e x p l a i n s m u c h o f t h e d i s c r e p a n c i e s a m o n g t h e l a t t i c e p a r a m e t e r s o f e a r l i e r i n v e s t i g a t i o n s . T h u s R a m a n (1967), w i t h o u t g i v i n g f u r t h e r details, l i s t e d X - r a y p o w d e r d a t a f o r a " C u - r i c h C e C u 0 . s S i t . 5 " [a = 4.136(5), c = 4.237(5)], as w e l l as a
" S i - r i c h C e C u 0 . s S i l . 5'' [a = 4.065(5), c = 4.302(5)]; l a t t i c e p a r a m e t e r s w e r e a l s o g i v e n f o r a C e C u l . s S i 0 . 5 w i t h A1B2-type [a = 4.238(5), c = 4.030(5); all s a m p l e s w e r e a r c m e l t e d ] . S i m i l a r l y G l a d y s h e v s k i j a n d B o d a k (1965) r e p o r t e d a = 4.077(2), c = 4.314(3) f o r t h e a l l o y C e C u 0 . s S i l . 5. F u r t h e r m o r e , R i e g e r a n d P a r t h 6 (1969a) m e a s u r e d a = 4.075, c = 4.280 f o r an a l l o y CeCu0.67Sil.33 a n d a = 4.124, c = 4.214 f o r C e C u S i ( X - r a y p o w d e r d a t a o f a r c - m e l t e d alloys). C o n s i d e r i n g t h e d a t a o b t a i n e d b y R a m a n (1967) a n d b y R i e g e r a n d P a r t h 6 (1969a) a w i d e r h o m o g e n e o u s r e g i o n o r e v e n a c l o s i n g o f t h e m i s c i b i l i t y g a p at h i g h t e m p e r a t u r e s s e e m s c o n c e i v a b l e . M a g n e t i c s u s c e p t i b i l i t y d a t a as p r e s e n t e d b y K i d o et al. (1983) f o r a n a l l o y C e C u S i p r e p a r e d b y p o w d e r m e t a l l u r g i c a l r e a c t i o n at 8 0 0 - 9 0 0 ° C f o r 7 d in e v a c u a t e d silica t u b e s r e v e a l e d a C u r i e - W e i s s b e h a v i o r in g o o d a g r e e m e n t w i t h t r i v a l e n t C e i o n s (A1Bz-type ,
~Lteff = 3 /~B, 0p = - 3 0 K , t e m p e r a t u r e r a n g e 7 7 - 3 0 0 K , n o m a g n e t i c m o m e n t w a s a s s u m e d o n t h e C u a t o m s ) .
Q u i t e r e c e n t l y I a n d e l l i (1983) o b s e r v e d t h e e x i s t e n c e o f a c o m p o u n d C e C u S i w i t h t h e o r d e r e d N i 2 I n - t y p e [ s u p e r s t r u c t u r e o f t h e A1B2-type, P 6 3 / m m c , a = 4.239(2), c = 7.980(4)]. T h e s u p e r s t r u c t u r e r e f l e c t i o n s w e r e said to b e v e r y f a i n t a n d w e r e o b s e r v e d in t h e X - r a y p a t t e r n s o f a r c - m e l t e d s a m p l e s a f t e r a n n e a l i n g at 750 o C f o r
PHASE EQUILIBRIA 15 8 - 1 2 d. W i t h r e s p e c t t o t h e d a t a o b t a i n e d b y R i e g e r a n d P a r t h 6 ( 1 9 6 9 a ) , G l a d y s h e v s k i j a n d B o d a k (1965), a n d R a m a n ( 1 9 6 7 ) o n a r c - m e l t e d a l l o y s , t h e N i 2 I n - t y p e p h a s e w a s c o n c l u d e d t o b e a l o w - t e m p e r a t u r e m o d i f i c a t i o n . N o t h e r m a l a n a l y s i s h a s b e e n c a r r i e d o u t y e t ; h o w e v e r , t h e c o r r e s p o n d i n g
c/a
r a t i o o b t a i n e d b y B o d a k e t al. (1974) f o r t h e p h a s e r a n g e CeCuH9_HoSi0.81_0.90 s e e m s t o b e i n d i c a t i v e f o r a N i z I n - t y p e l a t t i c e g e o m e t r y .F r o m D T A m e a s u r e m e n t s I s h i k a w a et al. ( 1 9 8 3 ) r e p o r t e d a c o n g r u e n t m e l t i n g b e h a v i o r f o r t h e c o m p o u n d CeCu0.sSil.5 w i t h a m e l t i n g t e m p e r a t u r e o f 1785 _+ 15 ° C.
C e S i l . s C u 0 . 2 ( c ~ - T h S i z - t y p e ) o r d e r s f e r r o m a g n e t i c a l l y a t T,~ = 6.5 K ( I s h i k a w a et al., 1983).
References
Aarts, J., F.R. de Boer and D.E. MacLaughlin, 1983, Physica 121B, 162.
Aliev, F.G., N.B. Brandt, E.M. Levin, V.V. Moshchalkov, S.M. Chudinov and R.I. Yasnitskii, 1982, Soy.
Phys. Solid State 24(1), 164.
Aliev, F.G., N.B. Brandt, V.V. Moshchalkov and S.N. Chudinov, 1983, Solid State Commun. 45(3), 215 and 47(9), 693.
Bodak, O.I. and E.I. Gladyshevskij, 1970, Nekot. Vop. Khim. Fiz. Poluprop. Slozhn. Sostava, p. 105.
Bodak, O.I., E.I. Gladyshevskij and P.I. Kripyakevich, 1966, Izv. Akad. Nauk SSSR, Neorg. Mater. 2, 2151.
Bodak, O.I., E.I. Gladyshevskij and Ya.M. Kalychak, 1971, Tesizy Dokl. Tret. Vses. Konf. Kristallokhim.
Intermet. Soedin (Lvov) p. 40.
Bodak, O.I., Ya.M. Kalychak and E.I. Gladyshevskij, 1974, lzv. Akad. Nauk SSSR, Neorg. Mater. 10(3), 450.
Bredl, C.D., H. Spille, U. Rauchschwalbe, W. Lieke, F. Steglich, G. Cordier, W. Assmus, M. Herrmann and J. Aarts, 1983, J. Magn. Magn. Mater. 31-34, 373.
Franz, W., A. Griessel, F. 'Steglich and D. Wohlleben, 1978, Z. Phys. B31, 7.
Gladyshevskij, E.I. and O.I. Bodak, 1965, Dopov. Akad. Nauk Ukr. RSR, Ser. A 5, 601.
Gschneidner Jr., K.A. and M.E. Verkade, 1974, Selected Cerium Phase Diagrams Document IS-RIC-7, Iowa State University, Ames, IA, USA, p. 18.
Hansen, M. and K. Anderko, 1958, Constitution of Binary Alloys (McGraw-Hill, New York) p. 629.
landelli, A., 1983, J. Less-Common Metals 90, 121.
lshikawa, M., H.F. Braun and J.L. Jorda, 1983, Phys• Rev. B27(5), 3092•
Jarlborg, T., H.F. Braun and M. Peter, 1983, Z. Phys. B52, 295•
Kido, H., T. Hoshikawa, M. Shimada and M. Koizumi, 1983, Phys. Stat. Sol. (a) 77, K12t.
Kletowski, Z., 1983, J. Less-Common Iyletals 95, 127.
• . . t .
Levln E . M . R . V . Lutslv L.D. Fmkel~em N.D. Samsonova and R.I. Yasnitskii, 1981, Fiz. Tverd. Tela , , , ~ '
23(8), 2401.
Lieke, W., U. Rauchschwalbe, C.D. Bredl, F. Steglich, J. Aarts and F.R. de Boer, 1982, J. Appk Phys.
53(3), 2111; see also 1984, Phys. Rev. Lett. 52(6), 469.
Padalia, B.D., T.K. Hatwar and M.N. Ghatikar, 1983, J. Phys. C16, 1537.
Raman, A., 1967, Naturwiss. 54, 560.
Rieger, W. and E. Parth6, 1969a, Monatsh. Chem. 100, 439.
Rieger, W. and E. Parth6, 1969b, Monatsh. Chem. 100, 444.
Sales, B.C. and R. Viswanathan, 1976, J. Low Temp. Phys. 23(3,4), 449.
Sampathkumaran, EM'., L.C. Gupta and R. Vijayaraghavan, 1979, J. Phys. C12, 4323.
~chneMner, H., Z. Kletowski, F. Oster and D. Wohlleben, 1983, Solid State Commun. 48(12), 1093.
Steglich, F., J. Aarts, C.D. Bredl, W. Lieke, D. Meschede, W. Franz and H. Schaffer, 1979, Phys. Rev.
Lett. 43, 1892; see also 1981, Phys. Rev. B23, 3171.
Stewart, G.R., Z. risk and J.O. Willis, 1983, Phys. Rev. B28, 172.
16 P. ROGL
~ Si 400°C
CeSi2 ~ ~ i i i ~ E u Si 2
Ce Eu
Fig. 6. Ce-Eu-Si, partial isothermal section at 400 °C (50-100 a/o Si).
Ce E u - S i
A p a r t i a l isothermal section of the system C e - E u - S i at 4 0 0 ° C has b e e n derived b y M o k r a (1979) b y m e a n s of X - r a y p o w d e r analysis of 44 alloy specimens. Samples were p r e p a r e d from 99.81% Eu, 99.56% Ce, a n d 99.99% Si b y arc m e l t i n g a n d were s u b s e q u e n t l y a n n e a l e d at 4 0 0 ° C for 350 h i n evacuated silica tubes. N o t e r n a r y c o m p o u n d s were formed. T h e m u t u a l solid solubilities of m o n o - a n d disilicides were derived f r o m the v a r i a t i o n of the lattice p a r a m e t e r s : o n l y small a m o u n t s of EuSi were s o l u b l e in CeSi (FeB-type, P n m a , a = 8.302, b = 3.962, c = 5.964), whereas a b o u t 20 mole% of CeSi dissolved in EuSi (CrB-type, C m c m , a = 4.70, b = 11.15, c = 3.99), linearly c h a n g i n g its u n i t cell d i m e n s i o n s to a = 4.66, b = 11.10, c = 3.95 at Eu0.sCe0.2Si (as read f r o m a small diagram). I n spite of the fact that b o t h CeSi 2 ( a = 4.20, c = 13.90) a n d EuSi 2 ( a = 4.31, c = 13.68) crystallize with the T h S i 2 - t y p e ( I 4 1 / a m d ) , the C e ~ E u l _ x S i 2 solid s o l u t i o n exhibits a two-phase region (miscibility gap) e x t e n d i n g at 4 0 0 ° C from Ce0.72Eu0.28Si 2 ( a = 4.23, c = 13.81) to Ce0.4Eu0.4Si 2 ( a = 4.30, c = 13.60). T h e b i n a r y c o m p o u n d Ce3Si 5 with G d S i 2 - t y p e ( I m m a ) was i n c l u d e d in the phase equilibria of the disilicide region by M o k r a (1979) (fig. 6) a n d o b v i o u s l y a c o n t i n u o u s t r a n s i t i o n was p r o p o s e d from the o r t h o r h o m b i c c~-GdSi2-type s o l u t i o n (Ce,Eu)3Si 5 to the tetragonal c~-ThSi2-type s o l u t i o n (Ce,Eu)Si 2 p h a s e ( n o d i s c o n t i n u i t i e s of lattice p a r a m e t e r s observed?). A m o r e detailed r e i n v e s t i g a t i o n of these c o m p l i c a t e d phase relations in fig. 6 will b e necessary. T h e dashed area i n fig. 6 r e p r e s e n t s the region of the a-ThSi2-type.
Reference
Mokra, I.R., 1979, Vestn. Lvov Univ., Set. Khim. 21, 52.
P H A S E E Q U I L I B R I A
TABLE 2
F o r m a t i o n and s t r u c t u r a l d a t a of t e r n a r y c o m p o u n d s C e - F e - S i .
17
C o m p o u n d S t r u c t u r e t y p e Lattice P r e p a r a t i o n , Refs. P u r i t y Space g r o u p p a r a m e t e r s C h a r a c t e r i z a t i o n
D e n s i t y
CeFeSi (*) P b F C I a = 4.062(3) arc, Qu, B o G K , 70b C e 99.56
P 4 / n m m c = 6.752(5) 800 o C, 250 h F e 99.96
OE = 6.54 single crystal d a t a B o G K C , 70a Si 99.99 O× = 6.64 H = 256 ( +_ 50) k g / m m 2
CeFe2Si 2 T h C r 2 S i 2 a - 3.991(1) 1 4 / m m m c = 9.881(5)
CeFeSi 2 CeNiSi 2
C m c m
Ce 2 FeSi 3 AIB2 P 6 / m m m
a = 3.986(10) c = 9.871(10) Px = 6.52
a = 3.995(6) c = 9.876(10) Px = 6.49 a = 4.094(3) b = 16.854(10) c = 4.031(3)
C e 99.91 T M ( f e r r o ) -- 470 K B o G L L , 77 F e 99.90 Si 99.99
arc, Qu C e 99.56
800 o C, 250 h, P X D B o G K C , 70a F e 99.96
H = 657 ( + 50) k g / m m 2 Si 99.99
a r c ( A r ) C e 99.56
P X D B o G K , 66 F e 99.9
Si 99.99 C e 99.91 T M (ferro) - 700 K B o G L L , 77 F e 99.90 Si 99.99
a r c ( A r ) , Qu, RiP, 69 high
900 ° C , 100 h, P X D p u r i t y
arc, Qu B o G K C , 70a Ce 99.56
800 ° C, 250 h, P X D F e 99.96
H = 707 ( _+ 50) k g / m m 2 Si 99.99
/xPi] r" = 2.94/~B; 0p = - 1 1 0 K
a - 4.065(2) arc, Q u
c = 4.191(2) 800 o C, 250 h, P X D H = 762 ( ± 50) k g / m m 2 a - 4.068(2) arc, Q u
c = 4.140(5) P X D
para
= 3 . 2 / * B ; 0 p = - 315
~eff
a = 4.058 i n d u c t i o n m e l t i n g c = 4.265 Ar, A1203 crucible, for CeFe0.4Sil. 6 1500 o C, Qu, 7 0 0 - 8 0 0 o C
2 4 - 9 6 h, P X D
Ce 99.91 B o G L L , 77 F e 99.90 Si 99.99 B o G K C , 70a C e 99.56
F e 99.96 Si 99.99 G I B , 65 C e 98.9 F e 99.9 Si 99.9 B o G L L , 77 C e 99.91
F e 99.90 Si 99.99 M a T , 69 C e 99.9 F e 99.95 Si 99.99
(*~ T h e crystal s t r u c t u r e of C e F e S i has b e e n r e f i n e d f r o m X - r a y single c r y s t a l p h o t o g r a p h s ( B o d a k et al., 1970b), R = 0.135. A t o m p a r a m e t e r s w e r e C e in 2c) 11/4, 1 / 4 , 0.672(1); Si in 2c) z = 0.175(2); Fe in 2a) 3 / 4 , 1 / 4 , 0. F r o m u n i t cell d i m e n s i o n s Ce was i n d i c a t e d to b e m a i n l y t e t r a v a l e n t .
18 P. R O G L C e - F e - S i
Phase equilibria in the system Ce Fe Si were determined by Bodak et al. (1970a) in two partial isothermal sections, at 8 0 0 ° C for the region 0 33 a / o Ce, and at 4 0 0 ° C for the region 33-100 a / o Ce, by means of X-ray and metallographic analysis of 125 alloys. Samples were prepared by arc melting under argon and subsequent annealing in evacuated silica tubes (400°C, 500 h; 800°C, 250 h).
Samples were also studied in as-cast condition, and those around the composition CeFe 7 were also annealed for 50 h at 1000 ° C; finally the allows were quenched in water. Etching was possible with aqueous solutions of HNO3, H F and glycerin.
Microhardness was determined at a load of 100 g. Starting materials were Ce 99.56%, Fe 99.96% and Si 99.99%.
The C e - F e binary system is in good agreement with a recent compilation of binary Ce systems by Gschneidner and Verkade (1974). Only two phases exist at 8 0 0 ° C : CeFe a with the MgCu2-type and c~-Ce2Fe17 at 84.5-88.5 a / o Fe with a defect Th2Znl7-type, corresponding to an approximate formula of CeFe 7. The binary Ce and Fe silicides were discussed in contect with the ternary systems C e - N i - S i and Y - F e - S i , respectively. Four ternary compounds were found to exist;
their crystallographic data are listed in table 2.
Solid solubilities were found to extend in the direction of a F e / S i exchange at a fixed Ce concentration. Solubility limits were determined from the variation of unit cell dimensions. Data have been presented for the Fe solubility in CeSi 2 (ThSi 2-type,
Si 800
Fe S i 2 ~ C e S[ 2
FeSi ~ ~ C e S i
//
// \c ssi3
\ \ 4ooo,
Fe
Ce Fe 7 Ce Fe 2 CeFig. 7. C e - F e - S i , partial isothermal sections at 800 o C (0 -33 a / o Ce) and at 400 o C (33-100 a / o Ce). 1:
CeFeSi, 2: CeFeaSi2, 3: Ce(Fe0.25Si0,v5)2, 4: CeFeSi 2.
