Yttrium-antimony alloy system

Journal of the Less-Common Metals Elsevier Sequoia S.A., Lausanne - Printed in The Netherlands

YTTRIUM-ANTIMONY

F. A.

SCHMIDT

AND

0.

ALLOY

SYSTEM*

D. McMASTERS

Institute for Atomic Research and Department of Metallurgy, go010 (U.S.A.) (Received

41.5

Iowa State University, Ames, Iowa

April 6th, 1970)

SUMMARY

A phase diagram is proposed for the yttrium-antimony system based on thermal, microscopic, chemical and X-ray analyses. An inverted peritectic reaction develops as a result of antimony additions, lowering the 1475°C transformation temperature of yttrium to 1462% Eutectic reactions occur at 14.5 at. o/oantimony and 1220°C, and greater than 99.0 at.% antimony and 629°C. There are four compounds in the system. The compound YSb melts congruently at 231o’C while Y&b and Y&b3 result from peritectic reactions at 1240’ and 1690°C. The fourth compound, Y&bs, forms peritectically at 212o”C, but decomposes by a eutectoid reaction at 1660°C.

INTRODUCTION

The purpose of this work was to study the phase relationships that exist between yttrium and antimony and to propose a phase diagram. This investigation is a continuation of our studies into the alloying behaviors of yttrium with elements of Groups IVA and VA (Pb, Sn, Ge, Bi and Sb). All of these metals have low nuclear cross sections and their characterization may be useful in determining if they have a potential use in nuclear design. Two compounds between yttrium and antimony have been reported. The compound YSb was first reported by BRIXNER~,and later confirmed by IANDELLI~,as being of the NaCl-type structure. MILLERAND HIMES~ estimated the melting point of this compound to be between 1800~ and 2ooo’C. The compound Y&b3 was observed as a second phase by GAMBINO~, in his study of the rare-earth antimonides and bismuthides. He reported this compound to melt incongruently and to have the antiThsPd-type structure. EXPERIMENTAL

PROCEDURE

Materials

The major impurities in the yttrium and antimony used in this investigation are given in Table I. The yttrium was prepared at this Laboratory by the magnesium * Work was performed in the Ames Laboratory bution No. 2710.

of the U.S. Atomic

J.

LeSS-COmWZO?8

Energy Commission.

Metals, 21

(1970)

Contri-

415-425

F. A. SCHMIDT,

416 TABLE ANALYSES

0.

D. MCMASTERS

I OF YTTRIUM

AND

Im+wity

Impurity

(P.P.m.) in Y -

Bi C Ca Cr CU Fe

<

METALS

concentration in Sb 3 n.d.* n.d. I I
30 < 10 40 25 140 (10 <5 40 300 -

Mg N Ni 0 Pb Si Sn Ta Ti Zr

ANTIMONY

20 -

(300 35 n.d.

* n.d. denotes element not detected spectrographically.

intermediate alloy processs. The antimony was obtained from the American Smelting and Refining Company and was used in the as-received condition. Alloy jweparation

The 20 g alloys used in this study were prepared by melting weighed amounts of the components in a sealed tantalum crucible. During the initial heating, a highly exothermic reaction occurs, at approximately 1100%. After this heat had been dissipated, heating of the samples was continued into the liquid region. Those alloys containing less than 50 at. o/oSb were subsequently homogenized by repeated melting. The alloys containing more than 50 at.% Sb were heated into the liquid region only once prior to the differential thermal analysis, since repeated meltirg resulted in excessive alloying with the tantalum container. About a third of the fifty-seven alloys prepared for this investigation were analyzed chemically for antimony. These alloys represented the more critical compositions across the system. A plot of their analyzed composition against their nominal composition was used to establish the antimony conteat of the other alloys studied. Since most of the yttrium-antimony alloys react with air, care was taken throughout the investigation to minimize exposure to the atmosphere. analysis Differential thermal analysis (DTA) was used to determine the liquidus curves and reaction horizontals of the system. Temperatures were measured potentiometritally and the specimen temperature and differential emf between the specimen and niobium standard were recorded on a X-X recorder. Temperatures up to 1550°C were measured by a Pt/Pt-I3Oh Rh thermocouple, shielded by high-purity alumina. A Thermal

j.

k%=COHW%OW

Metals,

21

(1970)

415-425

YTTRIUM-ANTIMONY ALLOYSYSTEM

417

W/W-2594 Re thermocouple, with beryllium oxide insulators, was employed to measure the higher temperatures up to 2250% The temperatures measured with the platinum-rhodium thermocouple were accurate to ) 5”C, while those for the tungstenrhenium couple had an estimated accuracy of + 10%. Samples in which a peritectic transformation occurred were held at a temperature just below the horizontal, to allow time for equilibration prior to thermal analysis. The liquidus curve between 48 and 53 at. ‘:/oSb was determined by sealing a portion of the alloy in a thin-wall tantalum tube, 0.4 cm in diam. and 8.9 cm long. This capsule was then heated under vacuum by electrical resistance, and the temperature of the wall was measured at thirty-second intervals using an optical pyrometer. The temperature at an inflection in the cooling rate curve was taken as the liquidus temperature. X-ray

and micrographic

methods

X-ray and micrographic examinations of the alloys of interest were carried out subsequent to the DTA measurements. Both powder and single-crystal X-ray diffraction methods were used to study the crystalline characteristics of these alloys. Copper, cobalt and chromium radiations were used and the specimens were prepared under a protective environment of argon gas. The powders were sealed in glass capillaries and the single crystals were coated with Apiezon N grease before they were mounted on glass rods with Duco cement. A computer program, written by JEITSCHKO ANDPARTHI?, was used to generate the crystallographic data for the known structures of the alloys. The generated values were compared with the observed sin20 and intensity data for the reflections of the powder patterns. The Nelson-Riley function was used in conjunction with the VOGEL-KEMPTER~extrapolation program to obtain the lattice parameters of the phases in the system. The single crystals were studied using Weissenberg and precession cameras. Oscillating crystal and n-level photographs were used to determine the lattice constants and space groups of the crystals. Specimens were prepared for microscopic examination by grinding on silicon carbide papers through 600 grit size and then through a Linde B cloth lap. The samples were examined and photographed in the air-etched condition. RESULTSANDDISCUSSION The yttrium-antimony phase diagram, shown in Fig. I, summarizes the results of this investigation. DTA was used to locate the horizontals associated with the inverse peritectic, eutectic, eutectoid and peritectic reactions. The phase boundaries were confirmed by chemical, microscopic and X-ray analyses. peritectic and eutectic reactions An inverse peritectic reaction occurs at the yttrium-rich end of the system at 1462 ) 5°C and approximately I at. o/0Sb. The evidence for this reaction was obtained from heating and cooling curves that showed a decrease of approximately 13°C in the o~+fi transformation of pure yttrium due to antimony additions. A eutectic reaction occurs at 14.5 at. y/oSb and 1220 + - 5°C as is indicated by the thermal data plotted in Fig. I. This composition was substantiated by the microstrucInverse

418

F. A. SCHMIDT, 0. D. MCMASTERS WEIGHT

2400

IO

20

30

40

I

I

I

I

PERCENT 50 I 2310

ANTIMONY 60

70

80

90

I

I

I

I

/s’ 2200

1800

1600 I521 1976 2

1400

W5 G E a I

1200

1000

z 800 _6?S°C

___

_

631

600

Y

IO

20

30

40 ATOMIC

Fig. I. Proposed yttrium-antimony

50 PERCENT

60

70

80

90

Sb

ANTIMONY

phase diagram and plot of thermal analysis data.

ture of a 14 at. yOSb alloy which exhibited a very small amount of primary yttrium in a eutectic matrix. The melting point of antimony is lowered about 2°C by small additions of yttrium, which is interpreted as the occurrence of a eutectic reaction at 6zg”C. This decrease was detected by a DTA method in which a sample of pure antimony was used as the standard specimen, thereby providing a more sensitive method for determining temperature differences. From microscopic evidence, the composition of this eutectic reaction is estimated to be greater than 99.0 at.% Sb. Intermetallic compounds Four intermetallic compounds, having the formulae Y&b, Y&bs, Y&b3 and

YTTRIUM--,%NTI%lONY ALLOY SYSTEM TABLE

II

POWDER PATTERN

DATAFOR

Y&b

WITH

THE T&P-TYPE

STRUCTURE

25 at.“/b Sb sample heat treated at 8oo*C for 5 days; CrKs radiation (A L-;;:2.29092 A). Obsevved --.

-

WM

o.oj*o

WM

0.0701

W WM WM

0.0775

'vii

0.5863 Cl.1130 0.1205

S

0.1474

vs

k

h

Intensity

0.1557

S

0.1729

S

0.1819

w

0.1895

MS

0.207g

WM

0.2160

s

0.2251

MW

0.2$3g

1

-.--_I__-I

1

I

2

I

2

0 I

2

0

2

I

3 3 3 3 1I 3 tI 4 4 i2 4 1‘2 3 4 I2 3 5 i3 5

I 0 I 2 0

0

3 I z 0 0 I I

0

1

Calculated ~. __._ .Si?228 Intrmity _~_ _____

U.05’5 0.0687 o.o773 0.0858 o.1116 0.1202 O.IJGO

2

0.1546

2 0

0.171s 2

0.1803 2

0.1889 0.2061

3 2 2 0 I I I

0.2147 0.2233 0.2576

117 36 79 x32 7 ‘4 246 281 237 ‘91 190 132 47 46 224 ‘52 21 200 208 hh 114 SS 47

Keflections omitted and h&l and K&Z data converted to Kn mean values to simplify listing. Also uot listed are the indices of equivalent and coincident reflections, but the calculated intensity values include the contributions from these reflections M

w MW M MW MW WM M MW W W W W M W W M 2

0.4905 0.5336 0.5672 0.5846 0.5932 0.6190 0.6528 0.66r9 0.6695 0.6866 0.6949 0.7045 0.7215 0.7306 0.7387 0.7645 0.7725 0.8075 0.8678 0.8936 0.9280 0.9451

‘2

I

3

I 2 I

5 4 I 2 0 6

0.6277

0.8423

z MW M M

7

ii 6

4

4 4 4 I 3 I 2 3 4 I I 3 3 4 1 2 I

: 5

4 3 3

4 j 0 3 3 4 0 I 2 I 3 I

0.4895 0.5325 0.5668 0.5840 0.5926 0.6183 0.6270 O.CjZ'/

0.66r3 0.6698 0.6870 0.69 j6 0.704’2 0.7214 0.7300

0.7386 0.7643 0.7729 0.8072 0.8416

0.8674 0.8932 0.9276 o.9.t46

90 72 135 57 72 36 125 $0 1x2 58 39 59 74 IZ5 ‘3 90 I75 52 II8 65 210 II0 II0 J34

F. A. SCHMIDT, 0. D. MCMASTERS

420

YSb, were identified in the yttrium-antimony system. Evidence for their existence, structures and melting characteristics is summarized below. Y&b (25.0 at.% Sb) : This compound forms by a peritectic reaction at 1240’ f5”C. Single crystals of this phase were obtained from samples of compositions 20, 25 and 30 at.% Sb. The best crystals were obtained from a 20 at.% Sb DTA sample which had been removed from the crucible and then arc-melted. Oscillation, equiinclination Weissenberg and precession photographs (CuKor radiation) showed the crystal to be tetragonal with a = 12.38 and c = 6.18 A. The reflections in the zero-, first-, and second-level Weissenberg photographs were indexed. The 4/m diffraction symmetry was observed in all these photographs. The hko reflections exist only when h + k = 2n and from the precession photographs 001 reflections exist only when 1= 212. The resulting P&z space group suggests that Y&b is isotypic with &r-Fe3 (P,J.~, B0.&8 for which the TisP-type structure has been adopteds. The powder patterns, using both CrKol and CuKol radiations, were indexed in their entirety on the basis of the single crystal parameters with a c/a ratio of 0.5. As shown in Table II, reasonable agreement between the calculated and observed sin28 and intensity data was obtained. The atom position parameters determined for TasSilo were used to generate the intensity values. The need for refinement of these positional parameters for the Y&b cell is reflected in the differences between the calculated and observed intensities, especially those planes for which h2+ k2 + Zz# 212 in the front reflection region. The observed intensity values of the single crystalpatterns are in good agreement with those of the powder patterns. A least squares fit of the powder data (CrKol radiation), in the back reflection region, yielded the extrapolated lattice parameters for the Y&b unit cell listed in Table III. TABLE

III

CRYSTALLOGRAPHIC DATA FOR Compound

Y&b YsSba

THE

YTTRIUM-ANTIMONY

Crystal system

Structure

S$ace

type

group

Tetragonal

TizP

P4zln

Hexagonal

MnsSip

Y&b3

Cubic

anti-ThsPd

YSb

Cubic

NaCl

INTERMEDIATE

adA)

Fmgm

co(A)

12.361

6.180

&

O.OOI

f

0.0005

f

*

9.1390 O.OOOI

8.9114

P63/mcm G3d

PHASES

f

6.1645 0.0005

Elemental volume contraction (Oh) 9.5

0.001

6.2960

18.1

fo.0006

-

16.7

-

7.9

The diffuse nature of the 311 (hkZ) line in the TasGe powder patterns led RosSTEUTSCHERAND SCHUBERT~Oto the determination of TaaGe (low temperature) of the TiaP-type and TaaGe (high temperature) of the FeaP-type. Since our Y&b powder patterns possess similar features, several sets of parameters for the body centered structures of both the FesP-type and Ti3Sbll were used in attempts to index these patterns. None of these trials was successful and single crystal methods yielded only the primitive tetragonal cell of the Ti3P type for Y&b. The Ti3P and related type structures are described in detail byRuNnQuIsTs~12, by ROSSTEUTSCHERANDSCHUBERT10, and by KJEKSHUS and coworker+. Most of the known Ti3P isostructural compounds are reported by ISJNDSTROM~~.The structure J. Less-Common Metals, 21 (1970) 415-425

YTTRIUM--ANTIMONY

ALLOY SYSTEM

421

types of known Max compounds, where M=groups VB, IVB, IIIB transition elements and X = Groups IVA, VA elements, are summarized in Table IV. Y3Sb is apparently the first TisP-structure-type compound involving either yttrium or antimony. In view of the trends suggested by the arrangement of structures of known phases shown in Table IV, the formation of Y&b in the T&P-type structure is not unexpected. The c/a ratios for the TiaP-type compounds listed in Table IV range from 0,495 to 0.508 and the c/a for Y&b is 0.50. Y&b with the TisP-type structure is compatible with the radius ratio borderline value between known representatives of the ‘l&I? and FesP-type structures presented by LUNDSTROM~~. For the Fe&type phases, YX/IMis greater than 0.82 and for the TiaP-type phases the radius ratio is less than 0.84. This ratio is o.80 for Y&b. The radius values listed by LAVES~~ were used, where rx=dlz = half the shortest distance observed in the element structures and ml% the Goldschmidt radius. TABLE

IV

STRUCTURE

V

Nb Ta

TYPES

OF SOME

Cr3Si T&J T&P

Ti Zr Hf

Ti# Tisf’

SC Y La

~ --

.&I&

PHASES

03Si CrsSi FC$Pa Ti3Pb

-

CrgSi Cr&i CrsSi

T&P TisP T&P

Cr&i T&P TiaP

C&i Cr&i Cr&i

NiaSn Cr3Si

T&P T&P TisP

CraSi TisP TkP(?)

CrsSiC Fe&’ FeaP

CuaAu

-

-

TisP -

-

--_I__

-

&High-temperature form. b Room-temperature form. c Body-centered tetragonal form also reported.

The crystallographic data for Y&b are summarized in Table III and the 9.594 contraction of the elemental volumes (24 Y and 8 Sb atoms) is in accord with that for isotypic phases. YeSb3 (37.5 at. 74 Sb) : The compound Y&b3 melts peritectically at r6go ) ro°C and crystallizes in the hexagonal ~n~Si~(D8~)-type structure. The crystallographic data for this phase are summarized in Table III and the excellent agreement between the calculated and observed sin‘@ and intensity data is shown in Table V. The atom position parameters determined by HOHNKE AND PARTI&~~ for GdsBis were used in these calculations. The lattice parameters of Y&b3 lie between those of Tb&bs and DysSbs determined by IZIEGER AND PARTHB 16. This placement of yttrium in the rare-earth series is a common result in comparative analyses of the properties of compounds containing rare-earth metals. Y&b3 (42.85 at.% Sb) : A unique feature of this system is that Y&b3 is stable only at high temperatures. It forms peritectically at 2120”+ 10°C and decomposes eutectoidally at 1660 +ro”C, as was shown by thermal, X-ray and microstructural J. Less-Common

Metals,

21 (1970)

415-425

F. A. SCHMIDT,

422 TABLE

V

POWDER PATTERN 38 at.%

DATA

FOR

Y&b3

WITH THE Mn&%-TYPE

Sb sampIe heat treated at rroo’C

k

h

Observed Intensity

0. D. MCMASTERS

-..

Sin2t9

M WM M MS

0.0104 0.0307

s

0.0709 0.0859

VVS

0.0909

M MW M MS W VW VW M S

0.2057

MW MW MS

0.2111 0.2204 0.2410

MS

0.2507

W M MW M M MS

0.2553 0.2660 0.2707 0.2808 0.2859 0.2962

0

0.0100

I

0

o.ozgg

0.0449 0.0600 0.0698 0.0700 0.0848 0.0898 0.0899

I

I

2

2

0

I

2

1

2

I

3

0

I

2

2

2

i

0.1011 0.1308 0.1358 0.1464 0.1505 0.1606 0.1654 0.1809

I

0

3 2

0

3 3 4

I

0

I

3

2

2

3 t2

I

2

I

3

4 4 0

0

5 13 2

0

3 4 4 3

2

4 2

3 3 2 0 I I 0

S

0.3107

M

0.3257

MS

0.3302

W W W

0.3401 0.3706 0.3850

M

0.4050

MS

2

2

4 I

5

3 3 13 4 3 4 5 {3

0.4149 M

1:

t: 6

0.4300

5

0.4451

i2

3 2 4 2

4 I I

1.54178 A).

0.0999 0.1297 0.1347 0.1447 0.1498 0.1596 0.1649 0.1797 0.2046 0.2048 0.2ogg 0.2196 0.2399 0.2494 0.2495 0.2547 0.2646 0.2695 0.2794 0.2844 0.2944 0.3093 0.3094 0.3097 0.3243 0.3245 0.3294 0.3297 0.3393 0.3696 0.3842 0.4041

Intensity 102

i%

236 239 82 1000 427 707 109 61 101

191 20 6 I.5

142 74 258 :; % 69 36 72 31 74 7= 64 23 190 46 37 34 37 108

23 22 31 28

0

0.4043 0.4143 0.4192 0.4290

40 37 30 45

3 5

0.4442 0.4446

22

3 3 2

(A =

Calculated

sirtze

_-

0.0457 0.0610

VS

1

STRUCTURE

for 4 h: CuKa radiation

73

data. This phase was not observed in the powder patterns of specimens taken from DTA sampIes with compositions between 40 aud 50 at. yOSb. A 43 at. % Sb alloy, heattreated for 7 h at 1750°C and subsequently quenched, exhibits a one-phase microstructure as is seen from Fig. 2. The powder patterns (Cu radiation) of this phase were indexed on the basis of the anti-ThsPa-type structure, and excellent agreement between J. ~&%S-COntPnO%

ik%&,

21

(1970)

415-425

423

YTTRIUM-ANTIMONY ALLOY SYSTEM

the observed and calculated data was obtained. A least squares fit of the back reflection data yielded the lattice parameter given in Table III. The lines were well resolved and the extra lines were attributable to the YSb phase. Microstructural evidence for the eutectoid decomposition of this phase was obtained by slow cooling a series of alloys from 18oo’C and by quenching samples just below the 1660°C horizontal. The microstructure of the 43 at.% Sb alloy, as cooled slowly from 2200°C, is shown in Fig. 3.

Fig. 2. Y-43 at.% Sb alloy, held at 1750°C for 7 h and quenched. polished, air-etched. ( x 250)

One phase YdSba. Mechanically

Fig. 3. Y-43 at.% Sb alloy, slow-cooled from 2250°C. Nearly complete eutectoid decomposition Y.&b3. Mechanically polished, air-etched. ( x 250)

of

YSb (50.0 at.% Sb) : This compound was found to melt congruently at 2310 + 35°C which is the highest melting phase in the system. It crystallizes in the NaCl type structure. Parameter values have been reported previouslyl,2*17. The lattice parameter given in Table III was obtained from powder patterns (Cu radiation) of samples with compositions, 46,50 and 60 at. o/oSb. Within experimental error the lattice parameter is the same for all these compositions. Alloys between 50 and IOO at.% Sb No additional compounds were found on the antimony side of the system. In the early stages of this investigation another phase was observed in the photomicrographs and powder patterns of specimens taken from DTA samples which had been heated three or four times into the liquid region. Some weak, nonreproducible thermal arrests were also recorded during these DTA runs. In an attempt to explain these observations, single crystals from a 65 at.% Sb alloy were analyzed by X-ray methods. The crystals were of two different shapes and quite regular in appearance. Those which were cube-shaped proved to be the YSb phase with the NaCl-type structure. The other, needlelike crystals were shown to belong to the monoclinic crystal class with lattice parameters corresponding to those of TaSbz listed in PEARSON~~. The suspected reaction between these alloys and the tantalum crucible material was J. Less-CommonMetals,

21 (1970)

415-425

424

F. A.

SCHMIDT, 0. D. MCMASTERS

therefore confirmed. For this reason the liquidus data shown in Fig. I for each alloy containing more than 50 at. o/oSb are based on a single thermal analysis. The crystal structure and lattice parameters for RSbz (R = La, Ce, Nd and Sm) compounds have been determined by WANG AND STEINFINK~~. These compounds crystallize in the orthorhombic LaSbz-type structure whereas the phase was not observed for R=Gd, Dy, Ho and Er. By using pressures up to 70 kbars with temperatures to ISOO’C EATOUGH AND HALLEYwere able to synthesize a number of RSb2 compounds including GdSbs and TbSbs of the LaSbz-type structure. Some “highpressure orthorhombic” RSbs (R=Gd, Tb, Dy, Ho, Er, Tm, Yb and Y) compounds were prepared, and in some cases “unknown products” resulted from these syntheses. Under the pressure and temperature conditions of this investigation, YSbz does not form and the powder patterns of alloys between 50 and 100% Sb show only YSb and Sb to be present. Terminal solid solubilities No attempt was made to accurately determine the terminal solid solubilities of this sytem. On the basis of photomicrographs and powder patterns of alloys containing 0.1 at.% Sb and 99.0 at.% Sb, the limits of solubility at low temperatures are considered to be negligible. CONCLUSIONS (I) An yttrium-antimony phase diagram is proposed which consists of an inverse peritectic reaction, two eutectic reactions and four intermetallic compounds. (2) Most of the alloys in the Y-Sb system are brittle and their reactive nature presents the problem of protecting them against attack by air and moisture. Considerable alloying with the tantalum container material was encountered with those alloys containing more than 50 at.% Sb. (3) The compounds Y&b and Y&b3 were identified and both result from peritectic reactions. Y&b3 forms peritectically at 212o’C but on further cooling decomposes eutectoidally at 1660°C. The compound YSbmelts congruently at about 231o’C. (4) No compounds were found between 50 and IOO at.% Sb.

ACKNOWLEDGEMENTS The authors would like to express their appreciation to 0. N. CARLSON and K. A, GSCHNEIDNER, Jr. for their consultation and support throughout this study. We also wish to thank D. M. BAILEY for his assistance in the single crystal X-ray study, and the Analytical and Spectrographic Sections of the Ames Laboratory for their work in performing the analysis of the yttrium metal and the various yttriumantimony alloys. REFERENCES I L. H. BRIXNER, J. Inorg. Nucl. Chews., 15 (1960) 199. 2 A. IANDELLI, in E. V. KTXRIZR (ed.), Rare-Earth Research, MacMillan, New York, 1961, p. 135. 3 J. F. MILLER AND R. C. HIMES, in E. V. KLEBER (ed.), Rare-Earth Research, MacMillan, New York, 1961, p. 232. J. h3Ss-CO??amOw Metals, 21 (1970) 415-425

YTTRIUM-ANTIMONY

ALLOY

SYSTEX

425

4 R. J. GAMBINO, J. Less-Common Metals, 12 (1967) 344. 5 0. N. CARLSON, J. A. HAEFLING, F. A. SCHMIDT AND F. H. SPEDDING, J. Electrochem.

(1960) 540‘ 6 W. ~~EITSCHKOAND E. PARTHE, A for&an IV proffram for the intensity calculation _ patterns, Univ. Pew., Lab. jov Res. o?a Str&cre‘;of Matter, 1965. 7 8 9 10

II 12 13 14 15 16

17 18

Sac., 107 of powvcler

K. E. VOGEL AND C. P. KEMPTER, dcta. Cryst., rq (1961) 1130. S. RUNDQUIST, Acta Chem. Stand., 16 (1962) I. T. LUNIXTROM AND P. 0. SNELL, Acta Chem. Stand., 21 (1967) , - .I x347. W. ROSSTEUTSCHER AND K. SCHWBERT, 2. Metallk., 56 (1965) Sri.‘A. KJEKSHUS, F. GRONVOLU AND J. THORBJORNSEN, Acfn Cham. Scawi., 16 (1962) 1493, S. RUNDQUIST, Arkiv Kemi, 20 (IQ&) 67. T. LUNDSTROM, Arkiv Kemi, 31 (1969) 227. F. LAW%, in Theory of Alloy Phases, Am. Sot. Metals, Cleveland, Ohio, 1956. D. HOHNKE AND E. PARTH~, J. Less-Commofa Metals, 17 (1969) 291. W. RIEGEK AND E. PARTI&, Acta Cryst., 324 (1968) 450, G. BRUZZONE, A. RUGGIERO AND G. OLCESE, Atti Accad. Nazi. Lincei Read., 36 (1964) 66. W. &MRsON, A ~~ndb~~k oj Lattice Spacings and St~l~~t~~~~s of Metals and Alloys, Vol.

Pcrgamon, New York, 1967. rg R. WANG AND H. STEINFINK, zo N. EATOUG~

AND H. T. HALL,

Inorg.

2,

Chem., 6 (1967) 1685.

Inorg. Chem., 8 (1969) 1439. J. Le.%-COmmO% Metals,

21 (1970) 415-x$25