Ag-Sm

The Ag-Sm (Silver-Samarium) System 107.8682 150.36

By K. A. Gschneidner, Jr. and F. W. Calderwood Iowa State University

Equi l ibr ium D iagram

The assessed phase diagram of the Ag-Sm system, shown in Fig. 1, is based on the work of Gebhardt et al. [64Geb], Steeb and Godel [65Ste], McMasters et al. [70Mcm], and Stapf et al. [80Sta],

Gebhardt et eL prepared alloys under argon in an electric arc furnace using a tungsten electrode and a water-cooled copper hearth. Their Ag was of 99.9995% (wt.?) purity and their Sm of 99% purity. Losses during melting were less than 0.3%. Alloys were reported to be homogeneous after one remelting. Thermal analyses were carried out under argon in an induct ion furnace at a cooling ra te of 50 ~ (which is ra ther excessive for reliable thermal analysis data). Samples were examined by microscopy and by the Guinier and the back-reflection X-ray techniques. These investigators reported three Ag-Sm compounds: Ag3Sm (melting point, 910 ~ Ag2Sm (peritectic for- mation at 770 ~ and AgSm (melting point 960 ~ In no instance was a solubility range observed by X-ray powder methods. Solubility of Sm was found to be less than 0.72 at.% at 775 ~ A eutectic between Ag and Ag3Sm was observed at 11.5 at.% Sm and 775 ~ The eutectic between AgaSm and Ag.~Sm was reported at 36 at.% Sm and 750 ~ The eutectic between AgSm and Sm was found at 76 at.% Sm and 690 ~ These investigators did not report on the solubility of Ag in ~, fi, or 7Sm.

Steeb and Godel [65Ste], who employed the Guinier X-ray method at room temperature and a high-temperature cam- era to 730 ~ reported only two intermediate phases, Ag3Sm and AgSm. Their X-ray investigation showed AgaSm to extend from 6 to 49 at.% Sm with a primitive orthorhombic unit cell containing "approximately 20 atoms". They reported AgSm to extend from 37 to 88 at.% Sm. They presented the phase diagram data of Gebhardt et al. without the Ag2Sm phase.

McMasters et al. [70Mcm] found Ag51Sm~4 to be the Ag- rich phase in this system. The chemical analysis of their Ag reported by Gschneidner et al. [70Gsc], and their alloy preparation and testing methods are given in [83Gsc] (Ag-La system). Their Sm metal contained 300 ppm by wt. Ta, <90 Ca, 80 O, 64 H, 35 Si, <35 Cu, <20 Mg, 18 N, and <200 total other rare earths. These authors suggested the possibility of a slight solubility range for the Ag~Sml~ stoichiometry and, because of the similarity in lattice parameters, they believed tha t the Ag3Sm parameters reported by Steeb et al. [68Ste] were actually for the AgslSm14 phase.

Iandelli and Palenzona [68Ian] made a structural study of Ag2RE compounds and observed Ag2Sm, which gave a complex powder pattern. A single crystal fragment ap- peared to be tetragonal with large lattice parameters, but its structure was not resolved.

Fig. 1 Ag-Sm Assessed Phase Diagram

�9

&

(D [--

2 0 3 0 4-( 1 o 0 0 . . . . . . , ~ , i

"~176 L IoOOJ

~ L g o C 9 3 5 O c

t: V~~

, o o - < E

? 5 0 0 -

4 0 0 -

Weight Percent Samar ium 40 5o 60 7o 80 90 too

. . . . . . . . i , , i . . . . . . . i . . . .

8 ~ 4 ~

1 0 ~ ~ I

/ " " ) ' S i n )

. : _ .~_ ~_ c_ _

,,,'(ps?~

675oC , '

= (Ag) (aSm) - . . . . . i . . . . . . . . . . . . . . . . . ~ . . . . . . - '~ l . . . . . . . . . . . . . . . , . . . . . . . r . . . . . . . i . . . . . . . i . . . . .

10 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1 0 0

Ag Atomic Percent Samar ium Sm

K.A. Gschneidner, Jr. and F.W. Calderwood, 1985.

142 Bulletin of All'oy Phase Diagrams Vol. 6 No. 2 1985

Ag-Sm

Stapf et al. 180Sta| r e inves t iga t ed this sys tem and re- ported conf i rmat ion of the compounds Ag3Sm (mel t ing point 935 ~ and AgSm (mel t ing point 960 ~ They also found the compound Ag2Sm, which forms per i tec t ica l ly at 790 ~ from Ag~Sm and liquid. The phase d iagram, which they constructed on the bas is of the rmal analys is , micro- s t r u c t u r a l e x a m i n a t i o n , and X-ray d i f f rac t ion , shows th ree eutectics: Ag-Ag3Sm at 10 at.% Sm and 760 ~ Ag2Sm-AgSm at 37 at.% Sm and 775 ~ and AgSm-Sm at 82 at.% Sm and 675 ~ The l iquidus l ine be tween the eutectic at 82 at.% Sm and Sm was drawn as a dashed line. No informat ion on the solubi l i ty of Ag in Sm was presented by these inves t iga tors .

Because Stapf et al. 180Sta] and Gebhard t et al. [64Geb] are the same group, the 1964 resul ts for th is phase dia- g r am have not been considered for Fig. 1 because the 1980 da ta are considered to supersede the ea r l i e r work. The phase d iagrams presented here are d rawn from tha t of S tapf et al., except the Ag-r ich compound is shown here as AgslSm~4. These d i ag rams indicate a solubi l i ty r ange from 21.5 to 25 at.% Sm as in the Ag-Ce system, wi th the peak in the l iquidus occurring a t some composition wi th in th is range. The solid solubi l i ty of Sm in Ag at the eutect ic t empera tu re is shown as - 1 at.%. S tapfe t al. repor ted this va lue as 2 at.%, bu t Gschne idner et al. [70Gsc] deter- mined the solubi l i ty l imi t of Sm in Ag to be 0.42 at.% Sm, wi th the eutectic occurr ing a t 781 ~ ins tead of 760 ~ as repor ted by Stapf. Gebha rd t et al. [64Geb] repor ted this solubi l i ty to be no more t h a n 0.72 at.% at 775 ~ These differences, pa r t i cu la r ly in the repor ted eutectic t empera- tures , may be due to differences in the pur i ty of the alloys, but not enough ana ly t i ca l deta i l was repor ted by Gebhard t et al. and Stapf et al. to jus t i fy a definite conclusion.

Thermodynamics

Garoche et al. [80Gar] m e a s u r e d the h e a t capac i ty of amorphous Ag79Smel, p repa red by rf sput te r ing . Af ter s u b t r a c t i n g the e l e c t ron i c (T) and phonon (0D) con- t r i b u t i o n s found for n o n m a g n e t i c Ag79Lu21 f rom the Ag79Sm2, data, the au thors found tha t the hea t capaci ty passed through a broad m a x i m u m near 4 K. Above 6 K

the hea t capaci ty decreased sharply, an indicat ion tha t the crystal electr ic field exci ta t ion does not contr ibute appre- ciably in th is t empera tu re range.

Cited References 59Dwi: A.E. Dwight and M.V. Nevitt, "Studies on Transition

Metal Intermediate Phases," ANL-6099, Argonne National Laboratory, Argonne, IL (1959).

60Ian: A. Iandelli, "Intermetallic and Metalloid Gadolinium Compounds," Atti Acad. Naz. Lincei Rend., Cl. Sci. Fis. Mat. Nat., 29, 62 (1960) in Italian.

63Cha: C.C. Chao, H.L. Luo, and P. Duwez, Jr., "Cs-C1 Type Compounds in Binary Alloys of Rare-Earth Metals with Gold and Silver," J. Appl. Phys., 34, 1971 (1963).

64Geb: E. Gebhardt, M. von Erdberg, and U. Lfity, "The Systems Silver-Yttrium and Silver-Samarium," Nucl. Met., 10, 303 (1964).

65Ste: S. Steeb and D. Godel, "On the Structure of the Phases AgSm and Ag3Sm," Z. Metallkd., 56, 612 (1965) in German.

68Ian: A. Iandelli and A. Palenzona, 'tOn the Occurrence of the MX2 Phases of the Rare Earths with the IB, IIB, and IIIB Group Elements and Their Crystal Structures," J. Less-Common Met., 15, 273 (1968).

688te: S. Steeb, D. Godel, and C. Lohr, "The Structure of the Compounds Ag3RE (RE = Y, La, Ce, Sm, Gd, Dy, Ho, Er)," J. Less-Common Met., 15, 137 (1968).

70Gsc: K. A. Gschneidner, Jr., O. D. McMasters, D. G. Alexander, and R.F. Venteicher, "Factors Influencing the Formation of Silver-Rich Solid Solutions in Rare Earth-Silver Alloy Sys- tems," Metall. Trans., 1, 1961 (1970).

70Mcm: O.D. McMasters, K.A. Gschneidner, Jr., and R. F. Ven- teicher, "Crystallography of the Silver-Rich Rare-Earth-Silver Intermetallic Compounds," Acta Crystallogr., B26, 1224 (1970).

78Bea: B.J. Beaudry and K.A. Gschneidner, Jr., "Preparation and Basic Properties of the Rare-Earth Metals," Handbook on the Physics and Chemistry of Rare Earths, Vol. 1--Metals, K.A. Gschneidner, Jr., and L. Eyring, Ed., North-Holland Pub- lishing Co., Amsterdam, 215 (1978).

80Gar: P. Garoche, A. Fert, J. J. Veyssie, and B. Boucher, "Specific Heat of Rate-Earth Amorphous Alloys," J. Magn. Magn. Mater., 15-18, 1397-1398 (1980).

80Sta: I. Stapf, G. Kiessler, H. Jehn, E. Gebhardt, and A. Mul- okozi, "The System Silver-Samarium," J. Less-Common Met., 71, P19-P27 (1980) in German.

83Gsc: K./~. Gschneidner, Jr. and F. W. Calderwood, "The Ag-La (Silver-Lanthanum) System," Bull. Alloy Phase Diagrams, 4(4), 370-374 (1983).

Ag-Sm Crystal Structure and Lattice Parameter Data Homogeneity Struktur-

range(a), Pearson bericht Space Proto- Lattice parameters, nm Density, Phase at.% Sm symbol designation group type a c Mg/m 3 Reference

(Ag) . . . . . . . 0 to -1 .0 cF4 A 1 Fm3m Cu 0.408626 .-- 10.494 [Landolt-BSrnstein] AgslSm14 .--21.5 to 25.5 hP65 ... P6/m Ag~lGd14 1.2644(b) 0.9299(b) 9.81(b) [68Ste]

1.2750(3)(c) 0.9381(2)(c) 9.564(c) [70Mcm] Ag3Pu, 1.271 0.9430 ... [80Sta]

deficient in Ag . . . . . . . . . . . . 1.59 2.97 ..- [68Ian]

cP2 B 2 Pm3m CsCl 0.3676(3) ... 8.63 [59Dwi, 60Ian, 63Cha, 65Ste] . . . . . . . . . . . . . . . . . . . . . [78Bea]

hP2 A 3 P63[._mmc Mg 0.36630 0.58448 ... [78Bea] hR3 C19 R3m aSm 0.36290(d) 2.6207(d) 7.520 [78Bea]

(c) Ag-rich side of diagram. (d) Lattice parameters are for the nonprimitive hexagonal

flAg2Sm . . . . . 33.3 hP? ... P63(?)

aAg2Sm . . . . . 33.3 AgSm . . . . . . . 50 (TSm) ....... 100

(flSm) . . . . . . . 100 (aSm) . . . . . . . 100

(a) From the phase diagram. (b) Sm-rich side of diagram. cell.

Ag-Sm evaluation contributed by K. A. Gschneidner, Jr., Director, and F. W. Calderwood, Rare-Earth Information Center, Ames Laboratory, Iowa State University, Ames, Iowa 50011. This work was supported by the Department of Energy through the Joint Program on Critical Compilation of Physical and Chemical Data coordinated through the Office of Standard Reference Data, National Bureau of Standards. Additional support was contributed by: Th. Goldschmidt AG, Essen, West Germany; Molycorp, Inc., Union Oil Co. of California, Los Angeles, CA; Reactive Metals & Alloys Corp., West Pittsburg, PA; Ronson Metals Corp., Newark, NJ; and Santoku Metal Industry Co. Ltd., Kobe, Japan. Literature searched through 1982. Professor Gschneidner is the ASM/NBS Data Program Category Editor for binary rare-earth alloys.

Bul le t in of Al loy Phase Diagrams Vol. 6 No. 2 1985 143