ANL-6856 Chemis t ry (TID-4500, 30th Ed.) AEG Resea rch and Development Report

ARGONNE NATIONAL LABORATORY 9700 South Cass Avenue Argonne, Ill inois 60440

A SEMINAR ON GROUPS V AND VI ANIONS

Compiled by

R. J . Bea l s , J. H. Handwerk and J. F . Schumar

Metal lurgy Division

March 1964

This Seminar , held at the Argonne National Labora to ry on 26 and 27 F e b r u a r y 1964, was jointly sponsored by the Metal lurgy Division of Argonne National Labora tory , and the Assoc ia ted Midwest Univers i t i es .

Opera ted by The Univers i ty of Chicago under

Contract W-31-109-eng-38 with the

U. S. Atomic Energy Commiss ion

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

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TABLE OF CONTENTS

Page

INTRODUCTION 5

SESSION I - THERMODYNAMIC PROPERTIES . 8

Thermodynamic P r o p e r t i e s of Selected Transi t ion Metal Phosphides 8

Decomposit ion P r e s s u r e s and Melting Points of Some

Actinide Mononitr ides 10

Thermodynamics of the Trans i t ion and Actinide Chalcogenides. 11

Initiation of Thermodynamic Studies of Some Chalcogenic Pnic t ides 13 The Diffusion of Sulfur-35 into Single Crys ta l s of Lead Sulfide as a Function of Stoichiometry and Doping Additions. . . . . . . . 14

P a r t i a l P r e s s u r e of Tcjlg) and MTe(g) along the Three Phase Lines of M^.^TexCc) (M = Ge, Sn, Pb) . 17

SESSION II - STRUCTURE AND PHASE RELATIONS 19

Crys ta l Chemis t ry of Some Rare E a r t h - Group V and VI Compounds 19

Varia t ion of the E lec t ros t a t i c Energy of the Wurtzi te S t ruc-tu re with Variat ion in the Cg/ao and uco Paranae te r s . . . . . . . . Z2

Cation Substitutions in Tungsten Diselenide and Its Analogues . 24

Stoichiometry and Defect Structure of Bismuth Tel lur ide . . . . . 26

P r o p e r t i e s and Phase Studies of Some Actinide Monophosphide

and Monosulfide Compounds and Related Binary System . . . . . 27

PuN and the Refractory Ni t r ides 30

SESSION III - MECHANICAL AND TRANSPORT PROPERTIES . . . . 34

Galvanomagnetic P r o p e r t i e s of Uranium Monosulfide and Uranium Monophosphide . . . . . . . . . . . . . . . . . . . . . . . . . . 34 E lec t r i ca l and Thermal P r o p e r t i e s of Group V and VI Amorphous and Pa r t i a l ly Recrys ta l l i zed Mate r i a l s . . . . . . . . . 35

TABLE OF CONTENTS

Page

Neutron and X-Ray Diffraction Studies of Som.e NiAs-Type

St ruc tures 38

P r o p e r t i e s of n - and p-Type PbSe 40

Elec t ron Spin Resonance P r o p e r t i e s of II-VI Compounds . . . . . 42

Elec t ronic St ructure of the Alkaline Ea r th Chalcogenides . . . . 43

SESSION IV - MAGNETIC AND TRANSPORT PROPERTIES . . . . . . 45

Reactor I r radia t ion and Annealing of PbTe and Bi2Te3. . . . . . . 45

E lec t r i ca l Conduction in R a r e - E a r t h Selenides 47

Thermoe lec t r i c P a r a m e t e r Studies of US, ThS, and US-ThS Solid Solutions 48

APPENDIX - Lis t of Attendees (Other than Argonne National Labora tory Personne l ) for the Seminar on Groups V and VI Anions . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

3

LIST OF FIGURES

No. Title Page

1. P r o g r a m Committee and Session Chai rmen 7

2. Speakers for Session I - Thermodynamic P r o p e r t i e s 8

3. Melting Point Apparatus 10

4. Decomposit ion P r e s s u r e of the Actinide Mononitrides 11

5. Heat Capacity of P4S3 14

6. Speakers for Session II - S t ructure and Phase Relations . . . . 19

7. Phase Diagram of the L a - T e System 20

8. Phase Diagram of the Nd-Te System 20

9. Phase Diag ram of the E r - T e System 20

10. Phase Diagram of the E r - S e System 20

11. Phase Diagram of the Yb-Sb Systera 21

12. Density at 25°C as a Funct ion of Liquid Composition 26

13. P r e l i m i n a r y Phase Diagram of the System UP-US 29

14. Phys ica l P r o p e r t i e s of Uranium and Plutonium Compounds . . 30

15. Pho tomicrograph of a P u - 8 5 w / o PuN Cermet 31

16. Photomicrograph of a PuN Specimen Showing Decomposit ion . 31

17. Thermal Stability of Selected Ni t r ides 32

18. Lat t ice P a r a m e t e r of PuN-UN Solid Solutions 33

19. Speakers for Session III - Magnetic and Transpor t

P r o p e r t i e s 34

20. Composit ional D iag ram for System Studied 36

21. Cor re la t ion of E lec t r i ca l Resis t iv i ty and Seebeck Coefficient. 37

22. Unit Cell of NiAs-Type Structure 38

23. Session Chai rman and Speakers for Session IV - Magnetic and Transpor t P r o p e r t i e s 45

24. Absolute Seebeck Coefficient vs Tempera tu re for Sintered Specimens of US, ThS, and US-ThS Solid Solutions 49

25. Resis t ivi ty as a Funct ion of T e m p e r a t u r e for Sintered Specimens of Uranium Monosulfide, Thor ium Monosulfide, and US-ThS Solid Solutions 49

4

LIST OF FIGURES

No. Title Page

26. The rma l Conductivity of Uranium Monosulfide. . . . . . . . . . . 50

27. Plot Showing Effect of Higher Sulfides on the Thernao-e lec t r i c Po^ver of Uranium Monosulfide . . . . . . . . . . . . . . . 51

LIST OF TABLES

No. Title Page

I P r o p e r t i e s of Some Actinide Monophosphide and Mono-sulfide Coinpounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

II. Atonaic and Ionic Radii . . . . . . . . . . . . . . . . . . . . . . . 39

III F igure of Mer i t as a Function of Tempera tu re for Uranium Monosulfide. . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

A SEMINAR ON GROUPS V AND VI ANIONS

Compiled by

R. J . Bea ls , J. H. Handwerk, and J. F . Schumar

INTRODUCTION

Compounds containing anions in Groups V and VI of the Per iodic Table of the E lements a r e becoming increas ingly impor tant in the fields of nuclear power, thermionic convers ion, semiconductors , and re la ted a r e a s of in te res t . F r o m pe r sona l communicat ions , it was known that considerable r e s e a r c h in the pnict ides and the chalcogenides was being c a r r i e d out in the indus t r ia l , nat ional , and univers i ty l abora to r i es of the country. However, months or y e a r s somet imes pass before a r e s e a r c h project has developed sufficiently to p e r m i t publication of the r e s u l t s .

This seminar was organized to p e r m i t and encourage a d i s s e m i -nation of information on cu r r en t s tatus of effort in the investigations of Groups V and VI anions. The l i t e r a tu r e contains considerable information on compounds whose anions a r e the oxides. It was decided that this s emi -nar would be l i ini ted to the chalcogenides (sulfides, se lenides , and te l lu-r ides) and the pnict ides (n i t r ides , phosphides , a r s en ide s , and antimonides) on which li t t le information was available in the l i t e r a tu re .

Contributions were sol ici ted froin the depar tments of c e r amic engineering, chemical engineer ing, cheni is t ry , meta l lurgy, and physics of the un ivers i t i e s in the United States and Canada; from s imi la r divi-sions in the national l abo ra to r i e s ; and from industr ia l l abora to r i es known or reputed to be working with these compounds. Response to the reques t was good.

Because of the nunaber of contr ibut ions from the un ive r s i t i e s , and because of the des i r e of the Assoc ia ted Midwest Univers i t ies to cosponsor this se in inar , the original commit tee , consist ing of Robert J. Beals , Joseph H. Handwerk, and Janaes F . Schumar, Argonne National Labora tory , was expanded to include rep resen ta t ion f rom univers i ty personnel . Added to the commit tee w e r e John H. Roberson, Executive Di rec tor of Associa ted Midwest Univers i t i es ; Car l Alexander , Battel le Memoria l Institute and Ohio State Universi ty; Chihiro Kikuchi, Univers i ty of Michigan; George C. Kuczynski, Univers i ty of Notre Dame; and Theodore J. Pianje , Missour i School of Mines and Mine ra l s .

The P r o g r a m Commit tee met at Argonne National Labora tory on 11 December 1963 and set up a tentative p r o g r a m from the contributions

available. Authors were reques ted to furnish abs t r ac t s of their p r e s e n t a -t ions , and the final p r o g r a m was es tabl ished. To p r e s e r v e an a tmosphere of informali ty, to p e r m i t adequate discussion, and to encourage the d i s -senaination of r ecen t data, the at tendance at the seminar was regulated.

The presenta t ion of s ta tus -of - the-work data prec luded the pub-lishing of a proceedings of the seminar . In an at tempt to make available the information presen ted , each speaker submitted a r e sume of his a d d r e s s . These r e s u m e s a r e the subject of this r epor t . A l i s t of p a r -t ic ipants , other than Argonne National Labora tory personne l , is given in the Appendix. Approxinaately 40 Labora to ry personnel par t ic ipa ted in the semina r .

The seminar was held in the Fue ls Technology Center , Argonne National Labora tory , on 26 and 27 F e b r u a r y 1964. The excellent technical p r o g r a m was complenaented by the capable handling of adminis t ra t ive a r r a n g e m e n t s by Dorothy A. Car lson and Leon S. Markheim, Labora tory D i r e c t o r ' s Office; El izabeth E. Wall is , Pe r sonne l ; and F r a n k M. Gentille, Graphic A r t s .

Assoc ia te Labora tory Di rec to r , Morton Hamermesh , welcomed the par t ic ipants to the Labora tory . He compared some of the r e s e a r c h in the a r e a of this seminar to Sir Isaac Newton's d iscovery of calculus. F r a n k G. Foote , Division Di rec to r , Metallurgy Division, Argonne National Labora tory , d i scussed the motivation for the seminar , explained some of the p r o g r a m s of the Labora tory , and es tabl ished the tenor of the semina r .

Four sess ions were held during the two-day meeting. Each speaker p re sen ted his p r o g r a m in approximately 20 minutes , permit t ing a 10-minute discuss ion on the m a t e r i a l p resen ted . The f i r s t sess ion was devoted to the thermodynamic p roper t i e s of coinpounds whose anions were Groups V and VI; the second sess ion was concerned with s t ruc ture and phase re la t ions ; in the thi rd and fourth se s s ions , the magnetic and t r anspo r t p rope r t i e s of the pnict ides and chalcogenides -w^ere discussed. F igure 1 shows the p r o g r a m commit tee and sess ion cha i rmen for the seminar .

At the dinner following the second sess ion , Lee C. Teng, Di rec tor of the P a r t i c l e Acce le ra to r Division, Argonne National Labora tory , de -scr ibed the construct ion detai ls and operating c h a r a c t e r i s t i c s of the newly const ructed Zero Gradient Synchrotron. The na ture and behavior of some of the h igh-energy pa r t i c l e s and applications of the synchrotron in thei r study compr i sed a second port ion of Dr. Teng 's presenta t ion .

7

Figure 1 Program Committet and Session Chairmen (left to right> Robert J Beals, Charles S. Barrett, James F. Schumar, Richard A Sivalm, Joseph H. Handwerk, and Robert J Thorn

20l -b l ;4

SESSION I - THERMODYNAMIC PROPERTIES

The f i r s t sess ion of the seminar , under the chairmanship of Robert J. Thorn, Argonne National Labora tory , was devoted to the cons ider -ation of the thermodynamic p rope r t i e s of conapounds whose anions included the pnict ides and chalcogenides. The speakers for this session a r e iden-tified in F igure 2.

Figure 2. Speakers for Session I: Thermodynamic Properties (left to right): Karl A. Gmgerich, William Olson, Edgar F. Westrum, Jr., H. L. Clever, J. Bruce Wagner, and R. F. Brebrick

r

!

2f 1-6217

Thermodynamic P r o p e r t i e s of Selected Transi t ion Metal Phosphides , Kar l A. Gingerich, Pennsylvania State Universi ty*

The vaporizat ion p rope r t i e s of selected t ransi t ion metal phosphides have been studied jointly with Dr. J. Efimenko of the National Bureau of Standards to obtain knowledge of thei r thermodynamic stability. ^ "^ F o r this purpose , a Knudsen effusion-mass spec t romete r assembly s imi la r to that descr ibed by Chupka and Inghram was used. This method pe rmi t s

*Work supported by the U. S. Atomic Energy Commission under con-t r a c t No. AT(30-1)-2541 with the Pennsylvania State Universi ty.

•'•Gingerich, K. A., and Efimenko, J . , Thermodynamics of Nuclear Mate r i a l s , International Atomic Energy Agency, Vienna, 1962, p. 477.

Gingerich, K. A., Proceedings of the Third Rare Ea r th Conference, V o r r e s , K. S., Editor (in p r e s s ) .

^Gingerich, K. A., Lee, P . K., and Efimenko, J. , Nature, 200, 774(1963).

"^Gingerich, K. A., Nature , 200, 877 (1963).

^Chupka, W. A., and Inghram, M. G., J. Phys . Chem., 59, 100 (1955).

the s imultaneous determinat ion of the composition of the gaseous phase , the p r e s s u r e of each of the gaseous spec ies , and the variat ion of each p r e s s u r e with t empera tu re and composit ion of the solid.

Included in the investigation w e r e the monophosphides of molyb-denum, tungsten, niobium, tantalum, t i tanium, z i rconium, hafnium, p raseodymium, and uraniuna, as well as t r i tho r ium tetraphosphide and the thor ium subphosphide.

All of these phosphides , except u ran ium naonophosphide, vaporize by decomposit ion into gaseous phosphorus and a condensed phase with lower phosphorus content. Uranium naonophosphide vapor izes p r ima r i l y by decomposit ion into gaseous u ran ium and phosphorus . No gaseous species containing both naetal and phosphorus atonas were establ ished.

The phosphorus ion in tensi t ies were measu red as a function of t empe ra tu r e and composit ion and re la ted to the respect ive pa r t i a l p r e s -su res by means of s i lver cal ibrat ion.

F r o i n the investigation of the phosphorus dissociat ion p r e s s u r e s as a function of composit ion of the condensed phase , it was found that, at the t empe ra tu r e of investigation, thor ium subphosphide and praseodymium. phosphide exhibit b road ranges of homogeneity that extend between the approximiate composi t ions ThPg^g-ThPo.fe and PrPi_o-PrPo_85> respect ively , while a - Z r P and TiP appear to have smal l ranges of homogeneity. No homogeneity ranges were detected for MoP, WP, a - Z r P , and Th3P4. In an X- ray investigation by D. W. Wilson, the solid solution of the thoriuna subphosphide was found to extend froiai ThPo.96-0.55 a-t 1000°C.

F r o m the invest igated t e m p e r a t u r e dependence of the phosphorus dissociat ion p r e s s u r e s that co r respond to the m e t a l - r i c h boundary cona-posit ion of the respec t ive phosphide, the pa r t i a l molal enthalpies of phosphorus decomposit ion, as well as the pa r t i a l molal free enthalpies at_2000°K, AG°2000 (Pj) were computed. The following values of AG°2000 (P2) in k i loca lor ies were obtained for the phosphides ThPo_£,, UP, a - Z r P (ZrPo_92)= TiPo.94, NbPo.94, MoP, Th3p4, and WP: 68.0, 64.7, 51.8, 25.8, 13.8, 2.2, 2 .1 , and - 2 . 1 , respec t ive ly . Although these a r e p re l imina ry r e su l t s , they give an indication of the s tabi l i t ies and s ta-bility t r ends among the phosphides invest igated. The stability of HfP -was found to be coinparable to that of ThPo_£, and UP, that of PrPo.9 was found to be between that of UP and a - Z r P , and the stability of TaP was found to be conaparable to that of a - Z r P . The phosphides from thorium subphosphide through a -z i rcon ium monophosphide and tantaluiai monophosphide a r e ne'w oxygen-free r e f r ac to ry laaaterials of high t he rma l stability that deserve considerat ion of their usefulness for special h igh- tempera tu re applicat ions. The s tabi l i t ies of the phosphides were compared "with those of corresponding

^Inghram, M. G., Chupka, W. A., and P o r t e r , R. F . , J. Chem. Phys . , 23, 2159 (1955).

10

ni t r ides . The vapor p r e s s u r e of uraniuna monophosphide was conapared with that of other uran ium compounds that a r e of in te res t in nuclear technology.

Decomposition P r e s s u r e s and Melting Points of Sonae Actinide Mono-n i t r ides , Will iam M. Olson, Los Alanaos Scientific Labora tory*

The n i t r ides of Th, U, Np, and Pu were naade by heating ei ther the metal or the hydride in ni trogen. Neptunium and plutonium ni t r ides were naade from the hydride because an adherent ni t r ide filial is formed which r e t a r d s further react ion. Thorium and uraniuin n i t r ides could be made sat isfactor i ly by d i rec t react ion with the me ta l s .

Snaall sanaples of the ni t r ide were placed in a 30° vee, fornaed in the center of a tungsten s t r ip which was mounted in a h i g h - p r e s s u r e furnace (Figure 3). This s t r ip was heated res i s t ive ly in a ni trogen a t -mosphere until melting occur red . The naelting point "was m e a s u r e d with

an optical py romete r , and the

Figure 3. Melting Point Apparatus

LIGHT

v.».

KEL-F fl

nu

c C

UD COPPER

ELECTRODE

WATER TO VACUUM SYSTEM

nitrogen p r e s s u r e was determined with a gauge of the appropr ia te range.

The data were plotted as log p ve r sus 10,000/T, and the r e -sulting curves a r e shown in F i g -u re 4. The ver t i ca l port ions of the curves cor respond to the t rue con-gruent laielting points : for ThN, 2790 ± 30°C; UN, 2850 ± 30°C; and NpN, 2830 ± 30°C. A congruent melting point could not be obtained for PuN because of p r e s s u r e l imitat ions.

It is not possible to de-termine the s tandard heats or entropies of formation for the n i t r ides from these data, because the liquid naetal p r e sen t after de-composition is sa tura ted with nitrogen and is therefore at some activity l e s s than unity.

626579 (Los Alamos) Sufficient thermodynamic data exist for UN and ThN to

*Work per formed under the auspices of the U. S. Atomic Energy Commission.

11

c a l c u l a t e the s t a n d a r d f r e e e n e r g i e s of f o r m a t i o n a t the e x p e r i m e n t a l t e m p e r a t u r e s . F r o m t h i s , a p lo t i s ob t a ined which i s the e x p e c t e d n i t r o g e n p r e s s u r e o v e r a h y p o t h e t i c a l e q u i l i b r i u m m i x t u r e of p u r e l iquid m e t a l and n i t r i d e , if n i t r o g e n did no t d i s s o l v e in the m e t a l . The o b s e r v e d p r e s -s u r e s dev i a t e m o r e and m o r e f r o m th i s l ine a s the t e m p e r a t u r e i n c r e a s e s and the so lub i l i t y of n i t r o g e n in the l i qu id m e t a l c o r r e s p o n d i n g l y i n c r e a s e s .

40 30 20'

1.0'

0.1

0.001

Figure 4

Decomposition Pressure of the Actinide Mononitrides

3.20 3.30" 3.40 3750 3.60" 3.70

lOOOO/T-oK^ 0 "3.80 S.tO

64936 (Los Alamos)

I t w a s p o s s i b l e t o a r r i v e a t a n e q u a t i o n of t h e t y p e l o g p = A + B / T + C T ^ f o r e a c h of t h e n i t r i d e s w h i c h f i t s t h e d a t a w e l l a n d a l l o w s e x t r a p o l a -t i o n of t h e d a t a t o I c w e r t e m p e r a t u r e s .

T h e r m o d y n a m i c s of T r a n s i t i o n a n d A c t i n i d e C h a l c o g e n i d e s , E d g a r F . W e s t r u m , J r . , U n i v e r s i t y of M i c h i g a n *

D u r i n g t h e l a s t e i g h t y e a r s w e h a v e h a d o c c a s i o n t o e x a m i n e t h e l o w - t e m p e r a t u r e h e a t c a p a c i t y of a b o u t 50 t r a n s i t i o n a n d a c t i n i d e c h a l -c o g e n i d e s p a r t i a l l y t o a s c e r t a i n t h e i r m a g n e t i c p r o p e r t i e s , t h e e f f e c t of s t r u c t u r e on t h e i r t h e r m a l p r o p e r t i e s , o r s o m e o t h e r s c i e n t i f i c a l l y i n -t e r e s t i n g a s p e c t of t h e i r t h e r m o d y n a m i c s . M y c o l l a b o r a t o r on m o s t of t h e s e s t u d i e s h a s b e e n D o s e n t F r e d r i k G r p n v o l d o f t h e U n i v e r s i t y of O s l o . A s f o r m e r s t u d e n t a n d p r e s e n t c o l l a b o r a t o r of P r o f e s s o r H a a k o n H a r a l d s e n , h e h a s d i s t i n g u i s h e d h i m s e l f i n t h e s t u d y of t h e d i f f i c u l t p r e p a r a t i v e a s p e c t of t h e s e c o m p o u n d s , a s w e l l a s i n t h e e l u c i d a t i o n of t h e i r s t r u c t u r e s , m a g n e t i c p r o p e r t i e s , a n d n a o r e r e c e n t l y t h e i r h i g h - t e m p e r a t u r e t h e r m a l p r o p e r t i e s a n d t h e r m o c h e m i s t r y .

*This research has been supported in part by the Division of Research of the U. S. Atomic Energy Commission.

A brief catalog of our studies (excluding the oxides) follows:

Molybdenum disulf ide ' (molybdenite, M0S2).

Chromium te l lur ides :7 CrTej^gg, CrTe^ 20' ^.nd CrTej_33.

Iron chalcogenides :^" •'•2 FeS , FeSi.14, FeS2 (pyr.), FeS2(naar.) , FeSeo_96, FeSei.14, FeSe^^^^, FeTeo.9, and F e T c j .

Nickel chalcogenides: 14-16 NiSei.05, NiSei.25= NiSe2, N i T e j i , NiTei_5, and NiTe2.

P la t inum chalcogenides:"7'17,18 p^g, PtSa, P t T e , PtTe2, Pd4S, Pd4Se, PdTe , and PdTeg.

Manganese dichalcogenides : ' MnSj, (MnSe2), and MnTe2.

Uranium c h a l c o g e n i d e s : ' ' -̂ US, USi_9, US2, US3, and USe2.

A major byproduct of this study has been the development of a scheme for es t imat ing entropies of chalcogenides on which no data a r e present ly avai lable . 13 This scheme has a lso been extended to include the important famil ies of lanthanide and actinide e lements . 1° '^^

West rum, E. F . , J r . , et a l . , unpublished data. "Wes t rum, E. F . , J r . , and Chou, C , Annexe 1955-3, Supplement au

Bulletin de I ' Insti tut Internat ional du Fro id , P a r i s , p. 308-10 (1956). "West rum, E. F . , J r . , and Grpnvold, F . , "Low Tempera tu re Phys ics

and Chemis t ry , " Proceed ings of the Fifth International Conference on Low Tempera tu re Phys ics and Chemis t ry , Madison, Wisconsin, p . 419-21 (1958).

lOCr/nvold, F . , and Wes t rum, E. F . , J r . , Acta Chem. Scand., 13, 241 (1959).

•'• ICrjOnvold, F . , Wes t rum, E. F . , J r . , and Chou, C , J. Chem. Phys . , 30, 528 (1959).

l^Wes t rum, E. F . , Jr. , Chou, C , and Grpnvold F . , J . Chem. Phys . , 30, 761 (1959).

l^Gr^nvold, F . , and Wes t rum, E. F . , J r . , Inorg. Chem. _1_, 36 (1962). l ^Wes t rum, E. F . , J r . , Chou, C , Machol, R. E. , and Gr^pnvold, F . , J.

Chem. Phys . , 28, 497 (1958). l^Wes t rum, E. F . , J r . , and Machol, R. E. , J. Chem. Phys . , 29, 824 (1958). •••"Grpnvold, F . , Thurnaann-Moe, T., Wes t rum, E . F . , J r . , and Levitin,

N. E . , Acta Chem. Scand., 14, 634 (i960). 1'Grpnvold, F . , Thurmann-Moe, T., Wes t rum, E. F . , J r . , and Chang, E. ,

J. Chem. Phys . , 35, 1665 (I96I) . •'•"Westrum, E. F . , J r . , Car lson, H. G., GrjZ^nvold, F . , and Kjekshus, A.,

J. Chem. Phys . , 35, 1670 (1961). 1/Westrum, E. F . , J r . , and Grpnvold, F . , Proceedings of the Symposium

on Thermodynamics of Nuclear Mate r i a l s , Vienna, p . 3-37 (1962). ^'-'Westrum, E. F . , J r . , " P r o g r e s s in the Science and Technology of the

Rare E a r t h s , " Volume I, p . 310-50 (1964).

13

As an example of the in t e re s t in these m a t e r i a l s , the situation in the manganese dichalcogenides ' will be reviewed briefly.

Initiation of Thermodynamic Studies of Some Chalcogenic Pnic t ides , H. L. Clever , Universi ty of Michigan and Emory Universi ty*

P las t i c c rys t a l s have been cha rac te r i zed by Timmermans'^-l as molecular compounds having an entropy of melting of 5 e.u. or l e s s . In addition, they usual ly have some if not all of the following p rope r t i e s :

- higher than nornaal vapor p r e s s u r e of the solid - higher melt ing points than other compounds of s imi la r molecular

weight and constitution - re la t ively easy deformation under p r e s s u r e - high naolecular and /o r c rys t a l symmet ry - one or m o r e (typically f i r s t o rder ) t rans i t ions to a nonplastic

c rys ta l l ine form at t e m p e r a t u r e s below the melting point.

We a r e in te res ted in a group of chalcogenic pnict ides that show p r o m i s e of being p las t ic c r y s t a l s . Ca lo r ime t r i c samples of the following have been p repa red :

N4S4 - a puckered ring s t ruc tu re . Changes color from orange to yellow at liquid ni t rogen t e m p e r a t u r e s .

|- cage s t ruc tu re of C3Y symmet ry . Transi t ions have been repor ted for both by w o r k e r s who originally p r e p a r e d them.22-24

- highly symmet r i c molecule .^^

The N4S4 was p r e p a r e d for our m e a s u r e m e n t s by Aaron Ribner; the phos-phorus compounds by Dr. A. W. Cordes , Universi ty of A r k a n s a s , Faye t t e -vi l le , Ark. , who is in te res ted in determining their s t ruc tu res and reac t iv i t ies ,

The hea t capacity and enthalpy of t rans i t ion of a one-eighth-mole sample of phosphorous sesqui sulfide, P4S3, have been studied by adiabatic ca lo r ime t ry f rom 5 to 350°K. The heat capacity, shown as a function of t empe ra tu r e in F igure 5, r evea l s an apparent ly f i r s t - o rde r sol id-sol id phase t rans i t ion at 313.95°K with enthalpy and entropy increments for the t rans i t ion of 2459 ca l /mole and 7.83 e.u., respect ively.

*This r e s e a r c h has been supported in p a r t by the Division of Resea rch of the U. S. Atomic Energy Coiaimission.

2 l T i m m e r m a n s , J . , Phys . and Chem. Solids, 1_8, 1 (1961).

22stock, A . , B e r . , 4 3 , 150 (1910).

23Mai, J . , Ber . , 59, 1888 (1926); 6_1, 1807 (1928).

24Keulen, E. , and Vos, A., Acta Crys t . , 12, 323 (1959).

25vos , A., and Wiebenga, E. H., Acta Crys t . , 8, 217 (1955).

Figure -5. Heat Capacity of P4S3

•I-

T h e l o v z - t e m p e r a t u r e c r y s -t a l s t r u c t u r e i s k n o w n to b e o r t h o -r h o i a i b i c ( D j t = P n a n b ) w i t h e i g h t l a i o l e c u l e s i n t h e u n i t c e l l . 2 6 ^ h e h i g h - t e i T i p e r a t u r e c r y s t a l s t r u c t u r e i s n o t k n o w n , b u t n a o s t p l a s t i c c r y s -t a l s a r e e i t h e r c u b i c o r h e x a g o n a l . A l t h o u g h c o n f i r i T i a t i o n of t h e p r e -s u m a b l y p l a s t i c n a t u r e of t h e C r y s -t a l I p h a s e m u s t a w a i t e x t e n s i o n of h e a t - c a p a c i t y d a t a to t h e t r i p l e p o i n t a n d d e t e r n a i n a t i o n of t h e e n -t h a l p y of f u s i o n , i t c a n b e r e a s o n a b l y a s s u m e d t h a t t h e C r y s t a l I p h a s e i s a l m o s t c e r t a i n l y p l a s t i c . S u c h n a e a s u r e m e n t s a r e c o n t e m p l a t e d in t h e n e a r f u t u r e , a n d a s i l v e r c a l o r i m -e t e r i s p r e s e n t l y u n d e r c o n s t r u c t i o n f o r t h i s p u r p o s e .

T h e o b s e r v e d e n t r o p y c h a n g e of t h e t r a n s i t i o n , 7 . 8 3 e . u . , i s 0 . 1 4 e . u

g r e a t e r t h a n R I n 4 8 . In p r i n c i p l e , a d e t a i l e d k n o w l e d g e of t h e a l i g n m e n t of t h e s y m n a e t r y e l e m e n t s of t h e m o l e c u l e w i t h t h o s e of t h e c r y s t a l l a t t i c e i n t h e p l a s t i c c r y s t a l p h a s e s h o u l d b e c o n s i s t e n t w i t h t h e o b s e r v e d e n t r o p y . 2 7 A l t h o u g h s p e c u l a t i o n s c a n b e m a d e n o w , a f i n a l r a t i o n a l i z a t i o n of t h e t r a n s i -t i o n e n t r o p y m u s t a w a i t d e f i n i t e k n o w l e d g e of t h e h i g h - t e m p e r a t u r e c r y s t a l f o r m .

U n d e r s t a n d i n g t h e t r a n s i t i o n s i n t h e s e m o l e c u l a r c o m p o u n d s a l s o m a y a s s i s t i n e l u c i d a t i n g t h e r o t a t i o n of r e a s o n a b l y s y m m e t r i c a l i o n s of s i m i l a r s i z e i n i o n i c c r y s t a l l a t t i c e s .

T h e D i f f u s i o n of S u l f u r - 3 5 i n t o S i n g l e C r y s t a l s of L e a d S u l f i d e a s a F u n c t i o n of S t o i c h i o m e t r y a n d D o p i n g A d d i t i o n s , M . S. S e l t z e r * a n d J . B r u c e W a g n e r , J r . , N o r t h w e s t e r n U n i v e r s i t y * *

I n r e c e n t p a p e r s , 2 8 - 3 0 r e s u l t s h a v e b e e n p r e s e n t e d a n d d i s c u s s e d

c o n c e r n i n g i n v e s t i g a t i o n s of l e a d d i f f u s i o n in s i n g l e c r y s t a l s of l e a d s u l f i d e .

*Present address is Battelle Memorial Institute, Columbus, Ohio. **This work was supported by the Office of Naval Research. 26Leung, Y. C , Waser, J., Houton, S. V., Vos., A., Wiegers, G. A., and Wiebenga, E. H., Acta Cryst.,

10, 574(1957). 2'^Gutherie, A. B., and McCullough. J. P., Phys. aad Chem. Solids, 18, 53 (1961). ^^ Anderson, J. S., and Richards, J. P.. J. Chem. Soc, (London), 537 (1946). 29Simkovich, G., and Wagner, J. B., J. Chem. Phys., 38, 1368 (1963). 3'JSeltzer, M. S., and Wagner, J. B., Jr.. J. Phys. Chem. Solids, 24 1.525 (1963).

It was concluded that lead diffuses via a lead vacancy,* Vp]-,, in undoped c rys ta l s containing excess sulfur. In undoped crys ta l s containing excess lead, it was concluded that lead diffuses as an inters t i t ia l species , Pb'j. In all c a s e s , equations of the form,

[cation vacanc ies ]apg^y[h]ma[e]™/pp |^ (1)

and

[ inters t i t ia l cat ions] a p p , / [ e ] ^ Cl [hP /pS (2)

were obeyed, where e and h denote an electron and an electron hole, respect ively , and m and n a r e positive exponents Avhose value indicates the degree of ionization of the defects. In this analys is , it was assumed that sulfur in lead sulfide c rys ta l s could not be p resen t as an in ters t i t ia l a tom because of its l a rge ionic radius (1.84 A) compared to that of divalent lead (1.32 A).

To gain further insight into t he^e fec t s t ruc ture of lead sulfide, e s -pecially the type and concentration of defects as a function of deviations from stoichiometry and foreign atom addit ions, diffusion studies using sulfur-35 were c a r r i e d out over the t empera tu re range_3fliIrI50__°C. Undoped siflgTe c r y s t a l s , and c rys ta l s doped with a donor (bismuth) and an acceptor (si lver) were p r epa red and equil ibrated under definite sulfur p r e s s u r e s as descr ibed e lsewhere .29 The t r a c e r Avas applied as a very thin layer , and the c rys ta l •was annealed under the same sulfur p r e s s u r e as during the p r e -diffusion anneal. The samples were quenched and counted using a flow counter and the res idual activity technique.

Resul ts on undoped c rys ta l s may be summar ized by

D | (in s to ichiometr ic PbS) = 6.80 x 10"^ expf-̂ ^—^—-E;—'• jcm^ sec"^ (3)

D* (in PbS + 10^8 excess S/cm^) = 4.56 x 10"^ e x p ^ ^ ' ^ ^ ~ ^ ' ^ ^ j cm^ sec"^

(4)

D* (in PbS -f 10̂ ® excess Pb/cm^) - 1.89 x 10"^ exp ( " ̂ ' ^ ^ ^ °'"^]cm^ sec"^

(5)

where the activation energies a r e in e lec t ron volts with the probable e r r o r l is ted, and the other t e r m s have their usual significance. Two points a r e

*The notation of F . A. Kroger and H. J. Vink is used he re .

16

to be made . F i r s t , the diffusivity of sulfur is as rapid a s , or more rapid than, that of lead. As a comparison, the diffusion of lead is given by ,""

D i , (in stoichioiTietric PbS) ~ 8.6 x 10"^ exp( - , ' ). (6)

Secondly, increas ing the chenaical potential of sulfur in PbS increased the isotheriaaal diffusivity coefficient of sulfur in PbS. Because diffusion is proport ional to the concentrat ion of defects, and because the Schottky equation,

[VpbJ [Vs] = K3, (7)

naust hold (activit ies must be used if the solution is nonideal), we make the folio-wing argument . Increasing the sulfur concentration in PbS inc reases the concentrat ion of cation vacancies , and according to equations (l) and (7), the anion vacancy concentrat ion is correspondingly depressed . There-fore jumps of sulfur into sulfur vacancies a re ruled out, because D^ in-c r e a s e s with decreasing [Vg ].

In further confirmation of this view, diffusion in bismuth-doped c rys ta l s yielded the following r e su l t s :

D* (in PbS + 2 X 10^9 Bi/cm^) = 3.38 x 10"

17

At 700°C, the dependence of the diffusivity on par t ia l p r e s s u r e of sulfur was tes ted a c r o s s the homogeneity range. Resul ts were plotted as log D^ v e r s u s log pq and compared with graphs of log [concentration of point defects] v e r s u s log pg (Kr5ger-Vink diagranas). On the bas i s of these compar i sons , a l ternat ive diffusion mechan i sms for undoped c rys ta l s were suggested as follows:

1) F o r all sulfur p r e s s u r e s except at the very high lead p r e s s u r e s ,

a) Migration as a neu t ra l species of in ters t i t ia l sulfur. b) Migration via cation vacancies . This naechanism is the

"counter -vacancy mechan i sm" proposed by Moore for oxides of copper , nickel , and zinc.-^-^ "-̂ -̂ We cannot d i s -t inguish between these two at p resen t .

2) At h igh l e a d p r e s s u r e s , the diffusion of sul fur w a s i n d e p e n d e n t of sulfujr c h e m i c a l p o t e n t i a l , a n d m i g r a t i o n v i a a defec t p a i r , [ V p b ] [Vg], w a s s u g g e s t e d .

S u m m a £1

The diffusion of su l fur in P b S o v e r the t e m p e r a t u r e r a n g e of 500° to 750°C w a s found to be a s r a p i d a s , o r naore r a p i d than , l e a d in P b S . Dif-fusion of su l fur v ia j u m p s in to an ion v a c a n c i e s -was r u l e d out.

P a r t i a l P r e s s u r e s of Te2(g) a n d M T e ( g ) a long the T h r e e - P h a s e L i n e s of M i _ x T e x ( c ) (M = Ge , Sn, P b ) , R. F . B r e b r i c k and A. J . S t r a u s s , L i n c o l n L a b o r a t o r y , M a s s a c h u s e t t s I n s t i t u t e of T e c h n o l o g y *

The op t i ca l d e n s i t y of the v a p o r c o e x i s t i n g wi th Mi_xTej j (c) of def ined c o m p o s i t i o n and t e m p e r a t u r e h a s b e e n m e a s u r e d b e t w e e n about 500° and 940°C. A r e c o r d i n g s p e c t r o p h o t o n a e t e r b e t w e e n 3100 and 4500 A, a n d / o r an i n t e r f e r e n c e f i l t e r - O s r a m Hg l a m p a p p a r a t u s wh ich i s o l a t e s the 4357 and the 3 6 5 1 - 3 6 6 4 A Hg l i n e s , a r e u s e d . The op t i ca l ce l l t e m p e r a t u r e i s kep t a t a f ixed h igh t e m p e r a t u r e whi le t ha t of the s i d e a r m con ta in ing the c o n d e n s e d p h a s e s i s v a r i e d b e t w e e n m e a s u r e -m e n t s . A s s u m i n g only two c o m p o n e n t s , Te2(g) a n d MTe(g ) , the da ta can be r e s o l v e d in to p a r t i a l o p t i c a l d e n s i t i e s u s i n g c a l i b r a t i o n r u n s wi th p u r e T e ( i ) . A s s u m i n g B e e r s ' l a w , r e l a t i v e p a r t i a l p r e s s u r e s for e a c h s p e c i e s and t o t a l and p a r t i a l e n t h a l p i e s a r e c a l c u l a t e d . Using the v a p o r p r e s s u r e of T e ( i ) and the r e s u l t s of p u b l i s h e d K n u d s e n ce l l e x p e r i m e n t s on the c o m p o u n d s , a b s o l u t e p a r t i a l p r e s s u r e s a n d to t a l and p a r t i a l f r e e e n e r g i e s a r e c a l c u l a t e d . V a r i o u s e x p e r i m e n t a l and t h e o r e t i c a l c h e c k s a r e m a d e to confirmi the i n t e r n a l c o n s i s t e n c y of the da t a and the va l i d i t y of the a s s u n a p t i o n s u s e d .

*Operated with support from the U. S. Air Force. 3lMoore, W. J.. Ebisuaki, Y., and Sluss, J. A.. J. Phys. Chem., 62, 1438 (1958). 32o'Keefe, M., and Moore, W. J.. J. Phys. Chem.. 65, 1438 (1961). 33Moore, W. J., and Williams. E. L.. Disc. Faraday Soc, 28, 86 (1959).

F o r compounds with ext remely na r row stabili ty ranges , such as PbTe(c) , a set of -well-defined composit ions is obtained by using t h r e e -phase samples in which the solid is e i ther naetal or te l lur ium saturated. (For SnTe(c) it is possible to p r epa re samples within the field of stability.) The m e a s u r e m e n t s so obtained a r e then along the th ree -phase lines of the compounds and give the ex t r emes in the par t ia l p r e s s u r e s of one component spec ies . The var ia t ion in pa r t i a l p r e s s u r e s observed can and has been undetected when samples of the "s to ichiometr ic" compound a r e used in p r e s s u r e m e a s u r e m e n t s .

F o r all th ree conapounds, the pa r t i a l p r e s s u r e of MTe(g) is constant over the field of stabili ty within an exper imental e r r o r of a few percent . At low tenaperatures and for the Te - sa tu ra t ed compound, Te2(g) is the p r e -dominant vapor species . F o r the me ta l - s a tu r a t ed compound, MTe(g) is the predominant spec ies . Some of the r e su l t s a r e tabulated below.

PbTe

^ SnTe

GeTe

at max imum melt ing point

T°C

924

806

725

(Torr )

PTe2

2.5

0.3

0.6 ± 0.3

^ M T e

11.8

0.86

17

at maximum value

° £ P T e ,

T°C

814

703

661

(Torr)

PTe2

12.5

2.4

2.5

PMTe

1.3

0.88

3.5

p(min)

-0 .01

0.015

0.11

kca l /mole

^Hfusxon

8 ± 0.8

11.3 ± 2

^Hsub

52

47

46

S E S S I O N I I - S T R U C T U R E A N D P H A S E R E L A T I O N S

T h e s e c o n d s e s s i o n of t h e s e n a i n a r w a s c o n c e r n e d w i t h c r y s t a l s t r u c t u r e a n d p h a s e r e l a t i o n s of t h e c o m p o u n d s c o n t a i n i n g G r o u p s V a n d VI a n i o n s . C h a r l e s S. B a r r e t t , I n s t i t u t e of M e t a l s , T h e U n i v e r s i t y of C h i -c a g o , w a s s e s s i o n c h a i r m a n . F i g u r e 6 s h o w s t h e s p e a k e r s f o r t h i s s e s s i o n .

Figure 6. Speakers for Session 11: Structure and Phase Relations (left to right) Hugo Steinfmk, William G. Gehmao, William T. Hicks, Che-Yu Li, Y. Baskm, and D. F. Carroll

201-6216

C r y s t a l C h e n a i s t r y of S o m e R a r e E a r t h - G r o u p V a n d VI C o m p o u n d s , H u g o S t e i n f i n k a n d E . J . W e i s s , T h e U n i v e r s i t y of T e x a s

T h e r a r e e a r t h - g r o u p V a n d VI s y s t e m s l a n t h a n u m - t e l l u r i u m , n e o d y m i u m - t e l l u r i u m , e r b i u m - t e l l u r i u m , e r b i u m - s e l e n i u m , a n d y t t e r b i u m -a n t i m o n y h a v e b e e n i n v e s t i g a t e d . T h e p h a s e d i a g r a m s of t h e s e s y s t e m s h a v e b e e n d e t e r m i n e d ; t h e c r y s t a l c h e n a i s t r y of t h e i n t e r n a e d i a t e p h a s e s h a s b e e n i n v e s t i g a t e d ; a n d t h e p h y s i c a l p r o p e r t i e s , s u c h a s e l e c t r i c a l c o n -d u c t i v i t y a n d S e e b e c k c o e f f i c i e n t , a r e u n d e r i n v e s t i g a t i o n . F i g u r e s 7 - 1 1 s h o w t h e p h a s e d i a g r a m s of t h e s e s y s t e m s . I t i s n o t u n e x p e c t e d t h a t t h e l a n t h a n u m - t e l l u r i u m a n d n e o d y m i u m s y s t e n a s a r e s o s i n a i l a r , w i t h t h e e x c e p t i o n of h i g h e r m e l t i n g - p o i n t t e m p e r a t u r e s f o r t h e n e o d y m i u n a c o m -p o u n d s a n d t h e a p p e a r a n c e of t h e c o m p o u n d N d j T e g . T h e e r b i u n a - t e l l u r i u m s y s t e n a d i f f e r s c o n s i d e r a b l y f r o m t h e L a a n d Nd s y s t e m s a n d m i g h t b e r e p r e s e n t a t i v e of p h a s e d i a g r a m s f o r t h e h e a v y r a r e e a r t h e l e m e n t s . T h e e r b i u m - s e l e n i u m p h a s e d i a g r a m d o e s n o t h a v e a s o l i d s o l u t i o n r a n g e f o r t h e 3:4 c o m p o s i t i o n ; t h e 1:3 c o m p o s i t i o n i s a b s e n t ; a n d 1:2 i n t e r m e d i a t e p h a s e s h o w s a p h a s e t r a n s i t i o n .

T h e y t t e r b i u m - a n t i m o n y s y s t e m , t h e o n l y s y s t e m -with a n e l e m e n t of G r o u p V s t u d i e d i n t h i s l a b o r a t o r y , r e v e a l s t w o p h a s e s t o w a r d t h e y t t e r b i u m - r i c h e n d of t h e p h a s e d i a g r a m .

Figure 7. Phase Diagram of the La-Te System

La-Te

La

..'i5751465

A \.

Te

Figure 8. Phase Diagram of the Nd-Te System

Nd-Te

Nd

1680 4620

I46Q

1 i 1 l is

Te Atom Percent Tellurium

Figure 9. Phase Diagram of the Er-Te System

Er-Te

\ /

\Z_1J50.

Er

\ \ \ \

\

„600_^

.i3JQj±: ^

Figure 10. Phase Diagram of the Er-Se System

Er-Se

Te Er

Atom Percent Tellurium Atom Percent Selenium

file:///Z_1J50

21

Yb-Sb

Figure 11

Phase Diagram of the Yb-Sb System

Yb Sb Atom Percent Antimony

Crysta l Chemis t ry

The 1:1 conapositions in these sys tems a r e usually labeled as hav-ing the sodium chloride type s t ruc tu re . The compounds LaTe, NdTe, and E r T e do not show X- ray diffraction intensi t ies whose Miller indices a re odd. Intensi t ies of such reflections a r e due to the difference in s ca t t e r -ing power of the two elenaents, and they a r e weaker than reflections with h k i even. Powder pa t t e rns , as well as single c rys ta l pa t te rns , fail to show any lines with h k i odd. It must be concluded that these s t ruc tu res have a prinaitive cell -whose lat t ice constant is one half of the usually r e -ported value (namely, approximately 3A), and they have one "atom" whose X-ray scat ter ing power is (R.E.)g sTeg^g in the unit cell . The ErSe phase is truly ordered , space group Fm3m, a = 5.66Z, and has the sodium chlo-ride s t ruc tu re . The compound YbSb s imi lar ly displays the d isordered s t ruc tu re .

The 3:4 composit ions of lanthanuna and neodynaium tel lur ides have the thorium phosphide, Th3P4, cubic s t ruc tu res , a = 9.628A and a = 9.456A, respect ively, and display solid folubility ranging to the composition 2:3. The corresponding e rb ium compositions a r e still par t of a solid solubility field -whose end m e m b e r s have the d i sordered cubic s t ruc ture and range from, the composition E r T e to Er3Te4. Apparently, in this sys tem the oc-cupancy of an atomic site can vary from a 50-50 percentage composition to the probabili ty that a te l lur ium atona will occupy a site 60 percent of the tinae. The Er3Se4-Er2Se3 solid solution has a much naore complex s t ruc tu re . It is or thorhombic , Fddd, a = 24.20A, b = 8.09A, c = 11.38A, with 12 Er3Se4 molecules or 16 ErjSes naolecules per unit cell . Never the-l e s s , a pseudo cubic unit cell , a = 9A, having a volume which is one- third of the orthorhonabic cell , can be chosen as a subcell. The subcell has the Th3P4 s t ruc tu re , as observed in the lanthanum and neodymium analogs.

,^.^ i4Kn 1500 1440 l^SO ^

^ - \ / / h"-

/ /

/ 1 /

\ / Al \

SI s

i\ i

•̂ H

m

>

\ \ \ 1000 \ /r«. v..

M

>

^ X \

\ \

A/_

22

The nauch more complex s t ruc tu re of the selenium conapound may be due to the difference in s izes of the atoiais. A c rys ta l s t ruc ture investigation is cur ren t ly in p r o g r e s s . Yb4Sb3 also has the Th3P4 s t ruc ture , a = 9.30, but no solid solution region can be detected.

The lanthanum and neodymium phase diagranas both contain a 1:2 to 1:1.7 solid solution. The te t ragonal unit cells with space group P|^mm a re a = 4,53A, c = 9.1lA, and a = 4.42A, c - 9.02A, respect ive ly . The c o r r e -sponding e rb ium selenide again shows a much m o r e complex c rys t a l s t r u c -ture and in addition has a phase t rans i t ion to a high-te nap e r a tu re foriai. The low- tempera tu re form is orthorhonabic, Bmcm, a = 1 5.8A, b = 11.88A, c = 16.22A, 48 laaolecules per unit cel l . A new, pseudo te t ragonal unit cell can be chosen by the following transfornaation: a' = a / 4 = 3,96A, b ' = b / 3 = 3,96 A, and c' = c /2 = S . l lA, which has two molecules per unit cell and is isonaorphous with the corresponding La and Nd conapositions. The h igh- tempera tu re forna is orthorhonabic, Inamna, a = 4.06A, b = 5.57A5 c = 13.16A. Again, the g rea t -er conaplexity of this s t ruc tu re naay be due to the difference in radi i of the atojaas. The c ry s t a l s t ruc tu re deternainations of these conapounds may p r o -vide the information to explain these differences. YbSbj is or thorhombic , a = 4.54A, b = 4.26A, c = 16.62A, Bnamb, and naay be a slightly d is tor ted s t ruc ture of the te t ragonal LaTe j and NdTeg. The YbjSb coiaapound is hex-agonal, a = 8.9 lA, c = 6.87A, P^-^cm.

The 1:3 conapositions encountered in the lanthanuna, neodymiuna, and erbiuna te l lur ides a r e all isonaorphous with unit cell dinaensions: LaTe3, a = 4.41A, b = 4.41A, c = 2 6 , M A ; NdTej, a = 4,35A, b = 4.35A, c := 25.80A; ErTe3, a = 4.31A, b = 4.3lA, c = 25.45A; space group Bnam,b. The LaTcj c rys t a l s invariably appear as twinned with a te t ragonal symmet ry .

Variat ion of the E lec t ros t a t i c Energy of the Wurtzi te Structure with Var ia -tion in the Cp/aQ and ucp Pa ranae te r s , "̂̂ Williana G. Gehiaaan, Atonaics Inte rnat ional*

A l inear plot is obtained when the Cg/ao ra t io is plotted against ucg (with a.Q = 1.000), the MX bond dis tance para l le l to CQ, for the few wurtzi te compounds for which u has been determined: the hypothetical ideally hexagonal -c loses t -packed wurtzi te s t ruc ture (abbreviated as W), BeOj and AIN, plus the recent addition of hexagonal Agl.35 These compounds have Co/aQ and u p a r a m e t e r s of:

*Research supported by U.S. Atomic Energy Conanaission, ^•^Gehman, W. G., Bull. Am. Phys . S o c , 9. 147 (1964), ^^Burley, G., J. Chem. Phys . , 38, 2807-2812 (1963).

23

compound

Agl W

BeO AIN

co/ao

1.635 1.633 1.623 1.600

u

0.374 0.375 0.378 0.385

The l inear (c|3/a0)-uCQ plot suggests the existence of a f ree-energy valley in which these compounds a r e const ra ined to lie. As pa r t of a study of the nature of this valley, the Madelung constant. A, has been determined for a s e r i e s of hypothetical wurtzi te s t ruc tu res covering wide variat ions of the Co/aQ ra t io and the ucg p a r a m e t e r . This study has been part ia l ly completed, and the r e su l t s to date, plus some of the p resen t tentative in te rpre ta t ions , a r e repor ted he r e .

F o r t y - t h r e e values of the Madelung constant have been calculated by the Ewald method.^" Two assumpt ions have been made for computa-tional convenience: (1) the ionic charges have been assumed to be -fl and - 1 ; and (2) ag has been fixed equal to 2rcp = 1.0000 for all calculat ions, where r^ is the rad ius of an ideally c loses t packed anion (i .e. , the en-t i re var ia t ion of the Cg/ag ra t io has been brought in through the Cg terna). Although these assumpt ions will affect the magnitude of the e lec t ros ta t ic energy associa ted with a given Madelung constant, they will not affect the naagnitude of the Madelung constant for the following reasons . F i r s t , the Madelung constant depends upon the rat io of the cha rges , but is independent of the actual values of the ionic charge . Second, the Madelung constant de -pends upon the shape of the unit cel l , but not upon its s ize . With these a s -sunaptions operat ive , the values of the Madelung constants , A, corresponding to s t ruc tu re s that a r e geoiaietrically s imi la r to W, BeO, and AIN a re 2,680, 2,686, and 2.699, respec t ive ly , with the re ference distance being taken as 2rcp. F u r t h e r , these three values lie on a l ine-of-minima in A-(co/an)-uco space which, upon being projected onto the (cg/ao)-ucg plane, coincides with the l inear plot mentioned in the f i r s t pa ragraph . Thus, pure Coulombic forces play a la rge role in determining the shape and orientat ion of the floor of the f ree -energy valley. As one deviates from the line -of-nainima toward sma l l e r values of ucg, the A values inc rease steeply, since the ca t -ion center is then moving direct ly toward the inamediately underlying anion center . Deviations toward l a rge r values of uCg lead to a shallo-w r i s e , since the cation now moves toward the center of an equi la tera l t r iangle of anions.

The negative of the Madelung constant is proport ional to the e l ec -t ros ta t ic energy, E ,-̂ Thus the above r e su l t s lead to a line-of-iaiaxinaa in Ee-(cg/ag)-uCo space, with a sha rp dec rea se in Eg upon moving toward snaaller UCQ values and a shallow d e c r e a s e upon moving toward l a rge r

36Ewald, P . P . , Ann. Physik, 64, 253-287 (1921). 37seitz, F . , Modern Theory of Solids, McGraw-Hil l , New York, 1940,

p. 76-82.

UCQ values . Approximate calculat ions of the over lap repulsion energy, E^,, have been made using the crude br"'^ Born relation,-3' with n being a r b i -t r a r i l y taken as 9, and with b being evaluated by the equation: b = ^ni^'^e " •'^t)' where E^ is the total lat t ice energy de termined by a Born-Haber cycle. A l ine-of -minima a r i s e s in Ej.-(co/ao)-ucg space which, upon projection onto the (cQ/aQ)-uCo plane, a lso coincides with the above-mentioned l inear plot for (co/ao)^1.6330 (thus the subscr ip t m, in the equation for b, denotes r values along the line - of-minima). Since the E miniiTia a r e nnuch s teeper than the Eg maxima, an energy valley a r i s e s in which the wurtzi te com-pounds a r e cons t ra ined to l ie, with their exact position there in being due to both atomic packing and covalency fac tors .

Cation Substitutions in Tungsten Diselenide and Its Analogues, William T. Hicks, E. I. du Pont de Neraours and Co., Inc.*

The substi tution of Group VB meta l s into tungsten diselenide leads to p-type semiconductors with potentially useful the rmoe lec t r i c p roper t i e s at high t e m p e r a t u r e s (600°C).38

The compounds WSej, MoSe2, and MoTe2 have a hexagonal s t ruc tu re of the MoSg type. Since these compounds do not mel t at s tandard p r e s s u r e , all m e a s u r e m e n t s were made on p r e s s e d powder b a r s . Due to the p la te-like c rys ta l s t ruc tu re of these compounds, these b a r s were found to have anisotropic e lec t r i ca l and the rma l r e s i s t i v i t i e s . All measu remen t s given in this paper were made in a d i rect ion perpendicular to the direct ion of p ress ing .

H igh - t empera tu re (600°C) p rope r t i e s have been m e a s u r e d on the compounds WSe2, MoSe2 and MoTe^ with the meta l s substi tuted to the ex-tent of a few percent by-tantalum. Of these m a t e r i a l s , the compos i -tion Wg_99 Tag oi^^a ^^^ ^'^^ bes t F igure of Mer i t with S = 313 /jv/deg, p = 9.6 mf i -cm, k = 23 m w / d e g - c m , and Z = 0.45'10"^ deg"^.

Niobium was found to be equivalent to tantalum in improving the p rope r t i e s of WSe2, but dissolved vanadium did not lower the res i s t iv i ty sufficiently. An a t tempt was made to substi tute acceptors from other groups of the periodic table into tungsten diselenide (for example, t i tanium, z i rconium, hafnium, and aluminum), but none of these was found to be ef-fective in lowering the res i s t iv i ty of undoped tungsten diselenide because of a lack of solubility, as shown by lat t ice paranneter m e a s u r e m e n t s . Donor

This work was supported in p a r t by the U.S. Navy Bureau of Ships Contract Nobs-84824. A port ion of this paper was presented at the spr ing nieeting of the E lec t rochemica l Society at Pi t t sburgh, Pa . , on Apri l 17, 1963. The complete manusc r ip t has been submitted for pos -sible publication in the Journal of the E lec t rochemica l Society.

^^Brixner , L. H., J. E l ec t rochem. S o c , 110, 289 (1963),

substi tut ions were a t tempted in n-type MoSeg with the e lements manganese , rhenium, ruthenium, and platinum, but of these only rhenium was apprec i -ably soluble. The composi t ion Mog^ggReQ^oz^^Z' which cor responds to the solubility lin^it of rhenium, yielded S = -286 /jv/deg and p = 28 mSl-cm at 600°C; thus with an es t imated value K = 30 mw/deg -cm, Z = O.MO"^ deg"* for this n-type m a t e r i a l . Donor substi tutions were also at tempted in tungsten diselenide with copper , nickel, i ron, and rhenium. Of these me t -a l s , only rhenium and i ron dissolved sufficiently to affect the e lec t r i ca l p roper t i es of tungsten dise lenide . They showed only slight solubility and tended to compensate the p-type cha rac t e r of tungsten diselenide, thus creat ing a m a t e r i a l with a higher r e s i s t ance than the undoped compound.

Attemipts were a lso made to substi tute in the anion si tes of these dichalcogenides. Antimony was found to be completely insoluble in tungsten diselenide, and iodine had lit t le effect when substi tuted in molybdenum diselenide.

Latt ice paramieter m e a s u r e m e n t s showed that the compound WSe2 has a very na r row homogeneity region and, therefore , little improvement can be made in the e l ec t r i ca l p rope r t i e s by varying the s toichiometry of the conapound.

Hall m e a s u r e m e n t s were made on the sys tem Wj.xTaxSeg as a func-tion of t empera tu re f rom room t e m p e r a t u r e up to 600°C. Since the Hall coefficient was found to be i so t rop ic , even though measu red on p r e s s e d powder b a r s which had anisotropic r e s i s t i v i t i e s , simple equations were used to re la te the Hall coefficients to c a r r i e r concentrat ions and mobi l i -t i es . For the composi t ion x = 0, the c a r r i e r concentrat ion amounted to about 3-10 cm"^ at room t e m p e r a t u r e , but s ta r ted increas ing at a t e m -pe ra tu re of about 400°C, indicating the onset of in t r ins ic behavior . F r o m the i nc rease in c a r r i e r concentra t ion with t empera tu re above 400°C, it was calculated that the energy gap is about 1.9 ev. This value is con-firmed by optical t r a n s m i s s i o n m e a s u r e m e n t s which yield a value of 1.6 ev.-^9 At the composi t ions x = 0,01 and 0.03, the ma te r i a l showed ex-t r ins ic semiconductor behavior ; that i s , the c a r r i e r concentrat ion stayed constant with varying t e m p e r a t u r e at the r e spec t ive values 6-10^^ cm~^ and 3-1020 c m " I

F o r the composi t ion range x = 0 to x = 0,05, the c a r r i e r mobil i t ies tend to conform to the law: jU va r i e s as T~°*^ except for the composi -tion X = 0.01 where the c a r r i e r mobility is a lmost constant with t e m p e r a -tu re . Thus in genera l the m a t e r i a l shows ionic lat t ice behavior.

Using c l a s s i ca l and F e r m i - D i r a c s t a t i s t i c s , excellent ag reement is found between the exper imenta l ly m e a s u r e d var ia t ion of Seebeck coefficient

^^Frindt , R. F . , J . Phys . Chem. Solids, 24, 1107 (1963).

26

with t e m p e r a t u r e for the above c o m p o s i t i o n s , and the b e h a v i o r p r e d i c t e d by the Ha l l coef f ic ien t m e a s u r e m e n t s m e n t i o n e d above . An effect ive m a s s r a t i o of 1.0 h e l d t h r o u g h o u t th i s c o m p o s i t i o n and t e m p e r a t u r e r a n g e .

S t o i c h i o m e t r y and Defec t S t r u c t u r e of B i s m u t h T e l l u r i d e , G. R. M i l l e r and C h e - Y u Li , C o r n e l l U n i v e r s i t y *

B i s m u t h t e l l u r i d e (Bi2Te3) i s an n - t y p e s e m i c o n d u c t o r if i t con -t a i n s e x c e s s t e l l u r i u m , and i s p - t y p e if it c o n t a i n s e x c e s s b i s m u t h . K r b g e r and Vink**^ have p o s t u l a t e d tha t de f ec t s in n o n s t o i c h i o m e t r i c b i s m u t h t e l -l u r i d e m a y be e s s e n t i a l l y the a n t i s t r u c t u r e t y p e . By a n t i s t r u c t u r e i t is m e a n t t ha t e x c e s s b i s m u t h (or e x c e s s t e l l u r i u m ) e n t e r s the l a t t i c e by r e -p l ac ing t e l l u r i u i n (or b i s m u t h ) . K r o g e r ^ l h a s f u r t h e r p o s t u l a t e d tha t for e v e r y five e x c e s s b i s m u t h a t o m s , t h r e e wil l be on t e l l u r i u m s i t e s , and t h e s e t h r e e a r e t h e r e f o r e e l e c t r i c a l l y a c t i v e . By s i m i l a r r e a s o n i n g , only two of e v e r y five e x c e s s t e l l u r i u m a t o m s a r e e l e c t r i c a l l y a c t i v e . The p u r p o s e of th i s w o r k i s to t e s t t h e s e p o s t u l a t e s e x p e r i m e n t a l l y .

B i s m u t h t e l l u r i d e s ing le c r y s t a l s of d i f f e r en t c o m p o s i t i o n s have b e e n p r e p a r e d by a mod i f i ed B r i d g m a n m e t h o d . "̂ The d e n s i t i e s of t h e s e c r y s t a l s w e r e m e a s u r e d by h y d r o s t a t i c weigh ing and a r e p lo t t ed v e r s u s l iquid c o m p o s i t i o n s in equ i l ib r iuna with t h e s e c r y s t a l s ( F i g u r e 12). The c r y s t a l g r o w n f r o m a l iquid of 62,8 a t o m i c pe t t e l l u r i u m is a s s u m e d to be

7 860

r 855

7.860

7 845

1 1 - 1 1 1

I \ \

__^ =i i=a».

- A

/ /

1 1 1 f 1

1 1" 1

-

• ~ " « s . ^ ^ -

^•..^'**^. "̂ '̂•43 ^ * \ *̂̂ A

\C"̂ "̂

1 I . J

Figure 12

Density at 25 C as a Func-tion of Liquid Composition. The solid line represents the experimentally deter-mined values. Curves I and II are the calculated densities based on anti-structure and vacancy models respectively.

60 61 62 63 «

ATOMIC PERCENT TELLURIUM IN LIQUID

65

^ T h i s project is supported by the Advanced Research Projects Agency. Kroger, F. A., and Vink, H. J., Solid State Physics, Vol. 3, Edited by Seitz and Turnbull, Academic Press, N. Y. (1956).

•̂ -̂ Kroger, F. A., J. Phys. Chem. Solids, 7, 276 (1958). Sattetthwaite, C. B., Ure, R. W., Jr., Phys. Rev,, 108 1164 (1957),

27

s to ich iometr ic , since it contains the min imum number of cur ren t c a r r i e r s as repor ted by Sat ter thwaite and Ure,42 and the value of its density coin-cides with that calculated from lat t ice paraixieters measu red by F r a n -combe.'*^ Crys ta l s with composit ions to the left of this point a r e bismuth r ich, and the ones to the right a r e te l lu r ium rich. It is easy to see from the shape of the exper imenta l curve that an t i s t ruc tu re type defects p r e -dominate on the b i s m u t h - r i c h side. However, it is not obvious that the same type of defect predominates on the t e l l u r i um- r i ch side.

Using the Hall coefficient data repor ted by Satterthwaite and Ure,'*^ and considering the many-val ley c h a r a c t e r of the band s t ruc ture of b ismuth te l lur ide ,44 the c u r r e n t c a r r i e r densi t ies can be calculated for the spec i -mens used in this work. Curve I in F igure 12 is calculated assuming that an t i s t ruc tu re type defects predonainate. In this case , each cu r ren t c a r r i e r cor responds to a misp laced atom. Curve II is calculated assuming that every two excess b ismuth atoms produce three holes due to the formation of th ree t e l lu r ium vacanc ies , and that every three excess te l lu r ium atoms produce two e lec t rons due to the formation of two bismuth vacancies . The difference between Curve I and the exper imenta l curve indicates that for b i smu th - r i ch al loys, the concentra t ion of the an t i s t ruc ture type defects is higher than that of the c u r r e n t c a r r i e r s . Severa l physical r easons may be used to explain this d iscrepancy. The mos t obvious one is that at high de -feet density, the chemica l concept of defect ionization loses its significance, andthe re la t ion between the number of cu r r en t c a r r i e r s and the number of defects is control led by F e r m i s t a t i s t i c s . If a s imi la r d iscrepancy of the same naagnitude exis ts on the te l lu r ium r ich side, the calculated Curve I will shift c lose r to the exper imenta l curve , leading to the conclusion that an t i s t ruc tu re defects predominate in the t e l l u r i u m - r i c h alloys also.

In summary , the exis tence of an t i s t ruc tu re type defects has been confirmed exper imenta l ly . However, the chemical concept of defect ion-ization fails to desc r ibe the e l ec t r i ca l behavior of the sys tem.

P r o p e r t i e s and Phase Studies of Some Actinide Monophosphide and Mono-sulfide Compounds and Related Binary Sys tems , Y. Baskin, Argonne Na-tional Labora tory*

The exis tence of compounds of actinide e lements with phosphorus and sulfur has been known for sonnetime. However, with the exception of some war t ime work, they have only begun to a t t r ac t ser ious attention in the past few y e a r s . Table I l i s t s the compounds of in te res t along with

*Work per formed under the auspices of the U.S. Atomic Energy Commiss ion.

•^^Francombe, M. H., Br i t . J. Appl. Phys . , 9.. 415 (1958). 44Drabble, J. R., P r o c . Phys . Soc. 77, 380 (1958). Drabble, J. R.,

Groves , R. D. ,and Wolfe, R., P r o c . Phys . S o c , 71, 430 (1958).

s e l e c t e d p r o p e r t i e s . T h i s r e s u m e s u m m a r i z e s r e s e a r c h on t h e s e c o m -pounds and r e l a t e d s y s t e m s conduc ted by a n u m b e r of w o r k e r s a t ANL.

T a b l e I

P R O P E R T I E S O F SOME ACTINIDE M O N O P H O S P H I D E AND M O N O S U L F I D E COMPOUNDS

Compound

ThPi„x U P P u P ThS US PuS

Lat t ice Constant

(A)

5.833 5.589 5.664 5.686 5,490 5.536

Density (g/cc)

8,83 10.23 9.83 9.51

10.84 10.61

Melting Point (°C)

ca. 3000 2540

-2330 2450

-

U P w a s s y n t h e s i z e d b y t h e r e a c t i o n a t 3 8 0 ° C of p h o s p h i n e g a s (PH3) w i t h f i n e l y d i v i d e d u r a n i u m d e r i v e d f r o m t h e h y d r i d e . 4 5 M a t e r i a l w a s t h e n h o m o g e n i z e d a t 1 4 0 0 ° C i n v a c u u m . U P i s a m e t a l l i c - a p p e a r i n g , b r i t t l e c o m p o u n d w i t h g o o d h i g h - t e m p e r a t u r e s t a b i l i t y . U P r e a c t e d w i t h 5% of u r a -n i u m a t 1 6 0 0 ° C to f o r m a n a n i o n - d e f i c i e n t s t r u c t u r e , a n d t h e u n i t c e l l c o n -t r a c t e d w i t h d e p a r t u r e f r o m s t o i c h i o m e t r y . T h e l a t t i c e c o n s t a n t a l s o c o n t r a c t e d o n h e a t i n g i n v a c u u m a b o v e 1 4 0 0 ° C , d u e to l o s s of p h o s p h o r u s ; w e i g h t l o s s e s o n l y b e c a m e s i g n i f i c a n t a b o v e 2 0 0 0 ° C . U P w a s c o m p a t i b l e w i t h M o , T a , a n d W u p t o a t l e a s t 2 0 0 0 ' ' C . U P s h o w e d n o r e a c t i o n w i t h UO2 u p t o 2 5 0 0 ° C , a n d n o e v i d e n c e w a s f o u n d of a n o x y p h o s p h i d e c o m p o u n d . O x i d a t i o n of U P w a s c o n s i d e r a b l y d i f f e r e n t f r o m t h a t of U A s , U C , U N , a n d US a n d w a s r e l a t e d t o f o r n i a t i o n o n t h e s u r f a c e of t h e g r a i n s of a v i t r e o u s c o a t i n g r i c h i n P2O5.

T h o r i u m p h o s p h i d e w a s s y n t h e s i z e d b y t h e p h o s p h i n e r e a c t i o n , f o l -l o w e d b y h o m o g e n i z a t i o n a t 1 3 0 0 ° C . T h e m a t e r i a l w a s b l u e a n d a p p e a r e d t o b e h y p o s t o i c h i o m e t r i c . I t e x h i b i t e d g o o d o x i d a t i o n r e s i s t a n c e a n d h a d a n u n u s u a l l y h i g h m e l t i n g p o i n t . T h e l a t t i c e c o n s t a n t w a s l i t t l e a f f e c t e d b y h e a t i n g a b o v e 1 4 0 0 ° C .

P l u t o n i u n r i p h o s p h i d e w a s p r e p a r e d b y t h e d i r e c t r e a c t i o n of t h e e l e m e n t s i n a n a r c f u r n a c e a n d i n a p r e s s u r e v e s s e l . 4 6

U S w a s p r e p a r e d b y r e a c t i n g f i n e l y d i v i d e d u r a n i u m w i t h H2S a t 4 0 0 ° C , f o l l o w e d by h e a t i n g i n v a c u u m a t 1 9 0 0 ° C t o h o m o g e n i z e t h e m a t e r i a l . ^

•^^Baskin. Y,, and Shalek, P. D., "Synthesis of Uranium Monophosphide by the Phosphine Reaction," J. Inorg. Nucl. Chem, (in press).

•^^Mosei, J. B., and Kruger, O. L., Ceram. News, 12 (10) 61 (1963) ABSTRACT. '̂ '̂ Shalek, P. D., J. Amer. Ceram. Soc, 46 (4) 155 (1963).

29

US h a s a m e t a l l i c a p p e a r a n c e wi th r o o m - t e m p e r a t u r e e l e c t r i c a l r e s i s -t iv i ty v a l u e s r ang ing f r o m 112 to 360 m i c r o h m - c m . Weight l o s s e s in v a c u u m of 1.2% p e r h o u r w e r e o b s e r v e d a t ISOCC. The compound showed a m o d e r a t e h o m o g e n e i t y r a n g e , but the effect of an ion v a c a n c i e s on the l a t t i c e c o n s t a n t was s m a l l . US showed no r e a c t i o n with Mo, Nb, Ta, X and W-26% Re a t 1980°C, bu t c o n s i d e r a b l e r e a c t i o n with Z r a t 1825°C. In t i m e , US p o w d e r s p i cked up oxygen, which r e s u l t e d in the f o r m a t i o n of r e l a t i v e l y l o w - m e l t i n g UOS, S i n t e r a b i l i t y of US w a s s t r o n g l y af fected by the p r e s e n c e of UOS, which r e s u l t e d in l i q u i d - p h a s e s i n t e r i n g a t 1800°C.

T h o r i u m m o n o s u l f i d e was s y n t h e s i z e d by the r e a c t i o n of t h o r i u m wi th H2S a t 700' 'C, fol lowed by h o m o g e n i z a t i o n in v a c u u m at 1900°C.'*'^ The compound w a s v e r y m e t a l l i c in a p p e a r a n c e and had low r o o m - t e m p e r a t u r e e l e c t r i c a l r e s i s t i v i t y v a l u e s ( 1 6 - 4 3 / i o h m - c m ) . S i n t e r a b i l i t y was good but was af fec ted by the p r e s e n c e of ThOS.

PuS i s be ing m a d e by r e a c t i o n of p a r t i a l l y d e h y d r i d e d p lu ton ium wi th HjS a t 400°C.48 Hea t ing of the r e a c t e d m a t e r i a l in v a c u u m at 1700°C r e s u l t e d in the f o r m a t i o n of PuS . The l iqu idus c u r v e showed a sha l low m i n i m u m n e a r the ThS end of the s y s t e m .

Sol id so lu t ion of UC and US was s u b s t a n t i a l , a l though m o r e UC e n t e r e d the US s t r u c t u r e than the r e v e r s e , 4 9 A m e l t i n g - p o i n t m a x i m u m of 2450°C o c c u r r e d in the s y s t e m at US 40% UC. UC 10% US exh ib i t ed b e t -t e r c o m p a t i b i l i t y than UC wi th Type 304 SS, Mo, Nb, Ta , and V in v a c u u m at IIBO'^C,

U P and US exh ib i t ed c o m p l e t e so l id so lub i l i ty , wi th the l a t t i c e c o n -s t a n t s a l s o showing a s l i gh t p o s i t i v e d e p a r t u r e f rom a s t r a i g h t - l i n e r e l a -t i o n s h i p . ^ ^ As s e e n in F i g u r e 13, a m e l t i n g - p o i n t m a x i m u m of 2600°C

2700

2600-

22

30

o c c u r r e d a t t h e c o m p o s i t i o n U P 30% U S . W e i g h t l o s s e s i n v a c u u m a t 2 2 0 0 ° C f o r U P w e r e l o w e r t h a n f o r U S , b u t t h e c o m p o s i t i o n U P 9 0 % US s h o w e d t h e g r e a t e s t l o s s e s . I n c o r p o r a t i o n of U P i n US i m p r o v e d t h e o x i -d a t i o n r e s i s t a n c e .

P u N a n d t h e R e f r a c t o r y N i t r i d e s , D , F . C a r r o l l , H a n f o r d A t o m . i c P r o d u c t s

O p e r a t i o n , G e n e r a l E l e c t r i c C o m p a n y *

W h y i s P u N b e i n g s t u d i e d ? C e r t a i n l y , w h e n o n e c o n s i d e r s a n u c l e -a r f u e l c a n d i d a t e h e l i k e s t o s e e h i g h v a l u e s f o r X - r a y d e n s i t y , f i s s i o n a b l e a t o m d e n s i t y , m e l t i n g p o i n t , a n d t h e r m a l c o n d u c t i v i t y . If o n e c o m p a r e s t h e s e d a t a f o r P u N w i t h t h o s e of P u O j a n d P u C , t h e a d v a n t a g e s of P u N a r e o b v i o u s ( F i g u r e 14) . F o r t h e r m a l c o n d u c t i v i t y , a n a l o g o u s u r a n i u m c o m -p o u n d s a r e c o m p a r e d , s i n c e t h e p l u t o n i u m c o m p o u n d d a t a a r e n o t a v a i l a b l e .

Figure 14. Physical Properties of Uranium and Plutonium Com.pounds

X-RAY DENSITY (g/cm3)

14.23

Pu DENSITY (g/cm3)

11,46

3,6 13.44

10.68

13.0

Pu02 PuN PuC

MELTING POINT C O

2 5 5 0

THERMAL CONDUCTIVITY (wat ts /cm-°C)

0.54

2 2 8 0

1654

0.03 t 1

0.25

UOg UN UC

P u N d o e s , h o w e v e r , offer a cha l l enge to ou r r e s o u r c e f u l n e s s . It a p p e a r s to h a v e a v e r y h igh d e c o m p o s i t i o n p r e s s u r e . To u s e P u N a s a h i g h - t e m p e r a t u r e fuel, i t m u s t be s t a b i l i z e d . A p o s s i b l e so lu t ion niay be to c o m b i n e PuN on an a t o m i c s c a l e wi th a m o r e s t a b l e n i t r i d e . The fo l -lowing e x p e r i m e n t a l da ta conapa re the t h e r m a l s t a b i l i t i e s of the

*Work p e r f o r m e d u n d e r C o n t r a c t No. A T ( 5 4 - 1 ) - 1 350 for the U.S. A t o m i c

E n e r g y C o m m i s s i o n .

m o n o n i t r i d e s of P u , U , T h , T i , a n d Z r . A s t u d y of t h e m i x e d n i t r i d e s w a s i n i t i a t e d w i t h t h e P u N - U N s y s t e m , a n d s o m e p r e l i m i n a r y p h a s e w o r k w i t h t h e o t h e r n i t r i d e s of i n t e r e s t .

T h e e f f e c t of a h i g h - d e c o m p o s i t i o n p r e s s u r e w a s f i r s t s e e n d u r i n g a n a t t e m p t to p r e p a r e s i n g l e - p h a s e P u N b y a r c - m e l t i n g a p l u t o n i u m m e t a l b u t t o n u n d e r o n e a t m o s p h e r e of n i t r o g e n . T h i s e x p e r i m e n t y i e l d e d a P u - 8 5 v o l % P u N c e r m e t ( F i g u r e 15) . D u r i n g a r c m e l t i n g , e q u i l i b r i u m c o n -d i t i o n s a r e n e v e r a c h i e v e d u n d e r t h i s l o w n i t r o g e n p r e s s u r e to o b t a i n s i n g l e - p h a s e P u N . T h e P u N i s no'w p r e p a r e d b y f i r s t h y d r i d i n g P u a t 2 5 0 ° C a n d t h e n n i t r i d i n g i t a t 8 0 0 ° C . T h e f i r s t m e l t i n g p o i n t of t h i s m a t e r i a l w a s r e p o r t e d to b e 2 7 5 0 + 7 5 ° C u n d e r o n e a t m o s p h e r e of n i t r o g e n . A p h o t o -m i c r o g r a p h of t h i s m e l t e d s p e c i m e n c l e a r l y s h o w s t h a t a d e c o m p o s i t i o n w a s o c c u r r i n g ( F i g u r e 16) . T h e s t r u c t u r e i s i d e n t i c a l t o t h a t of t h e a r c -m e l t e d m a t e r i a l . R e c e n t e x p e r i m e n t s u s i n g a t u n g s t e n r i b b o n f u r n a c e y i e l d a n a p p a r e n t u i e l t i n g - p o i n t v a l u e of 2 556 ± 15°C u n d e r o n e a t m o s p h e r e of p r e p u r i f i e d n i t r o g e n . T h e p r e s e n c e of PUO2 a s a c o n t a m i n a n t l o w e r s t h e m e l t i n g p o i n t t o 2 4 0 0 ° C . A P u O j - W r e a c t i o n m a k e s i t d i f f i c u l t t o o b -t a i n p r e c i s e v a l u e s .

Figure 15. Photomicroj^raph of a Pu- Figure 16. Photomicrograph of a PuN Specimen 85 \v/o PuN Cermet. Shov»ing Decomposition

T h e t h e r m a l s t a b i l i t i e s of t h e n i t r i d e s m e n t i o n e d p r e v i o u s l y , P u N , U N , T h N , T i N , Z r N , a n d a s o l i d s o l u t i o n P u N - 5 0 m o l % UN, w e r e c o m p a r e d b y h e a t i n g t h e s e n i t r i d e s f o r f o u r h o u r s a t 1800°C u n d e r a p p r o x i m a t e l y 600 m m N2, A r , A r - 8 % H j , a n d a 10"^ T o r r v a c u u m . T h e p e r c e n t - w e i g h t l o s s w a s t a k e n t o b e i n d i c a t i v e of t h e t h e r m a l s t a b i l i t y of t h e n i t r i d e ( F i g -u r e 17) . I t i s p a r t i c u l a r l y n o t i c e a b l e t h a t T h N , T i N , a n d Z r N a r e q u i t e s t a b l e u n d e r v a c u u m . N o t e a l s o t h a t t h e P u N - U N s o l i d s o l u t i o n i s o n l y

s l igh t ly b e t t e r than a t w o - p h a s e m i x t u r e . Weight l o s s e s of t h e s e n i t r i d e s u n d e r n i t r o g e n , a r g o n , and a r g o n - 8 % h y d r o g e n w e r e neg l ig ib l e . In a d d i -t ion to t h e s e w e i g h t - l o s s e x p e r i m e n t s , the m e l t i n g b e h a v i o r of e a c h of t h e s e n i t r i d e s was d i r e c t l y o b s e r v e d in a t u n g s t e n r i bbon f u r n a c e . The P u N m e l t i n g e x p e r i m e n t s w e r e d i s c u s s e d p r e v i o u s l y . UN under one a t -m o s p h e r e of n i t r o g e n a p p e a r e d to m e l t b e t w e e n 2670°C and 2840°C. F a i l -u r e of the t u n g s t e n r i bbon , p r o b a b l y due to a r e a c t i o n wi th the UN o r a d e c o m p o s i t i o n p r o d u c t , o c c u r r e d a t t e m p e r a t u r e s a s low a s 2630°C. Rap id v o l a t i l i z a t i o n of the s a m p l e was obvious a t 2730°C. The m e l t i n g b e h a v i o r of ThN w a s o b s e r v e d u n d e r A r , Nj, and v a c u u m . U n d e r one a t m o s p h e r e of A r , the a p p a r e n t m e l t i n g poin t w a s 2550°C. V o l a t i l i z a t i o n a t th i s t e m -p e r a t u r e w a s obv ious . U n d e r one a t m o s p h e r e of n i t r o g e n , ThN a p p e a r e d to be s t ab l e to 2680°C. At low p r e s s u r e s , 10"^ T o r r , ThN vo la t i l i z ed a t 2250°C. The w e i g h t - l o s s e x p e r i m e n t s showed i t to be qui te s t ab le a t 1800°C in vacuuna. T iN w a s m e l t e d u n d e r one a t m o s p h e r e of n i t r o g e n . The f i r s t s ign of i n s t a b i l i t y of one s a m p l e was a t 2930°C. A s u b s e q u e n t r u n on th i s s a m e s a m p l e y i e l d e d a va lue of 2860°C. A l s o , a s e v e r e t u n g s t e n r e a c t i o n w a s o b s e r v e d . Z r N v o l a t i l i z e d and a t t a c k e d the t ungs t en r i b b o n a t 2960°C u n d e r one a t m o s p h e r e of n i t r o g e n .

Figure 17. Thermal Stability of Selected Nitrides

100

yACUU^̂ , i800°C 4hours

53

19

II 0 86 0

PuN PuN UN ThN TiN ZrN 50 mol % UN

Study of the m i x e d n i t r i d e s b e g a n with the P u N - U N s y s t e m . Minus 325 m e s h p o w d e r s of P u N - U N c o m p o s i t i o n s a t 25 mol% i n t e r v a l s w e r e b l ended and p e l l e t i z e d . They w e r e h e a t e d in a t u n g s t e n c r u c i b l e for four h o u r s a t 1800°C u n d e r 500 m m of a r g o n . Solid so lu t ions as d e t e c t e d by X - r a y d i f f rac t ion w e r e ob t a ined a t a l l c o m p o s i t i o n s . The X - r a y r e s u l t s a r e shown in F i g u r e 18. Note , h o w e v e r , so l id so lu t ions could not be f o r m e d b e t w e e n PuN and ThN, TiN, o r Z r N a f t e r five h o u r s a t 1800°C u n d e r 500 m m a r g o n . Only at 2000°C for four h o u r s u n d e r 500 m m n i t r o g e n was s o m e

90

80

70

o -• 50

S 40 S

30

20

10

33

success obtained with one of the mix tu res , PuN-25 m.ol% ZrN, X-ray dif-fraction indicated that solid solution formation had begun, but had not gone to completion.

4.916

.912

4,888

Figure 18, Lattice Parameter of PuN-UN Solid Solutions

— ,912

4.916

40 50 60 MOLE PERCENT UN

What next? Fu r the r mixed nitr ide work will be done with PuN-UN, -ThN, and -ZrN. The solid solution studies with ThN in PuN were not encouraging, but the concept does look at t ract ive as a fast b reeder - type fuel. The melting behavior of in teres t ing ni tr ides will be studied soon in a h igh -p re s su re furnace capable of 3000°C at 150 a tmospheres p r e s s u r e . The decomposit ion problem associa ted with PuN may be reduced if the PuN is incorporated in a ce rmet . Therefore , some fuel loss studies will be conducted using PuN containing ce rme t s formed by a pneumatic impac-tion p roces s .

In conclusion, PuN looks very a t t rac t ive from the standpoints of density, melting point, and probable the rmal conductivity, but it does have a ser ious drawback, its high decomposit ion p r e s s u r e . A solution to this problem may lie in a mixed nitr ide such as PuN-ZrN, or a cernaet system.

The paper "Crys ta l Growth and Surface Charac te r i s t i cs of III-V and II-VI Compounds as Related to S t ruc ture , " was to have been presented by Har ry C. Gatos, Massachuse t t s Institute of Technology. Professor Gatos was ill and was unable to be presen t at the seminar .

34

SESSION n i - MECHANICAL AND TRANSPORT PROPERTIES

Richard A. Swalin, Universi ty of Minnesota, was chairman of the th i rd sess ion of the senainar. Discussion in this sess ion dwelt on the mag-netic and t r anspor t p roper t i e s of the Groups V and VI anion-containing connpounds. Speakers for this sess ion a re shown in F igure 19.

Figure 19. Speakers for Session III: Magnetic and Transport Properties (left to right) M. A. Kanter, E. B. Hensley, James H. Healy, Chihiro Kikuchi, A. J. Strauss, and S. S. Sidhu.

201-6218

Galvanomagnetic P r o p e r t i e s of Uranium Monosulfide and Uranium Mono-phosphide, Manuel A. Kanter and Casinair W. Kazmiercwicz , Argonne National Laboratory*

Uranium monosulfide (US) and uran ium monophosphide (UP) a r e two compounds of the actinide metals with cations of Groups IV, V, and VI which crys ta l l ize in the NaCl s t ruc tu re , and have high melting points and high e lec t r i ca l conductivit ies. E lec t r i ca l res i s t iv i ty , Hall effect, magne to re s i s t -ance, and magnetization measu remen t s "were made on s in tered polycrys ta l -line samples of the tAvo compounds in the t empera tu re range, 4.2-300°K, to elucidate the e lectronic s t ruc ture in these cubic actinide compounds.

US was found to be fer romagnet ic with a Curie point at 180°K and a sa turat ion magnetic moment of 1.02 Bohr magnetons per U atom at 0°K. The e lec t r ica l res is t iv i ty was found to be about a hundred t imes l a rge r than m the common fer romagnet ic me ta l s , but the t empe ra tu r e dependence was s imi la r , showing an abnormal dec rease below the Curie point. The mag-ne tores i s tance was smal l , except near the Curie point where there Avas a la rge negative value. Study of the Hall effect revealed that two Hall coeffi-cients could be identified as in the t rans i t ion meta l s . The ext raordinary

*Based on work performed under the auspices of the U. S. Atomic Energy Commiss ion.

Hall coefficient re la ted to the magnet izat ion was found to vary as the 2.1 power of res is t iv i ty in reasonable agreement with previous theor ies of this effect. The ord inary Hall coefficient re la ted to the applied field was found to be posit ive and t empera tu re -dependen t , whereas in the f e r r o m a g -netic me ta l s the Hall coefficient is found to be tempera ture- independent , with the exception of an anomalous behavior near the Curie point. A s imi la r anomaly is observed in US which occurs over a voider t empera tu re range than in the common fe r romagne t ic m e t a l s . The effective c a r r i e r concen-t ra t ion evaluated from the ord inary Hall coefficient is 0,45 hole per U atom at absolute z e r o .

UP has been r epor t ed to be ant i fer romagnet ic with a Neel t e m p e r a -tu re of IZO^K.Sl The m e a s u r e m e n t s made he re were on samples containing 2-5% P vacancies and a r e somewhat p re l imina ry . All the samples m e a s -ured showed e l ec t r i ca l r e s i s t i v i t i e s about one- th i rd that of US with a sharp break at the Neel point. The Hall coefficients were smal l and negative at 4.2°K but became posi t ive somewhat above this t e m p e r a t u r e . They became la rge in the vicinity of the Neel point and dec reased toward room t e m p e r a -t u r e . An effect due to sca t te r ing of sp in-polar ized e lec t rons s imi la r to that in the fe r romagne t ics is indicated. However, magnet ic susceptibil i ty m e a s -u remen t s must yet be c a r r i e d out.

These r e su l t s can be co r re l a t ed with a band p ic ture based on ove r -lapping 7s and 5f. bands, where the s ta tes in the broad 7s band contribute the major conductivity, whereas the magnet ic behavior is due to unpaired spins of e lec t ron s ta tes in the n a r r o w 5f̂ band. Equi l ibr ium between the bands r equ i r e s a red i s t r ibu t ion of e lec t rons bet^veen them as the t e m p e r a -tu re v a r i e s , giving r i s e to the observed tenapera ture-dependence of the galvanomagnetic p r o p e r t i e s . S imi la r m e a s u r e m e n t s on the i so s t ruc tu ra l actinide compounds and the i r solid solutions will provide a c r i t i ca l tes t of this model .

E l e c t r i c a l and T h e r m a l P r o p e r t i e s of Group V and VI Amorphous and P a r -t ial ly Recrys ta l l i zed M a t e r i a l s , J a m e s H. Healy, Spindletop Resea rch , Inc.*

This paper p r e s e n t s information regarding the p rope r t i e s of m a t e -r i a l s p r epa red by combining a r s e n i c , thal l ium, antimony, sulfur, selenium, and te l lu r ium. An apprec ia t ion is obtained of the energy c a r r i e r s in h e t e r -ogeneous or amorphous s t r u c t u r e s .

The e lements used in the sample synthesis were all of the 99.999% puri ty. S to ichiometr ic p ropor t ions Avere sealed in evacuated Vycor tubes

*H. L. Uphoff a s s i s t e d with the work at the A. O. Smith Corporat ion, Milwaukee, Wisconsin, under Navy cont rac t NONR 2965(00)-Al.

Trzebia towski , Sepichowska. Suski and Troch, 19th Internat ional Congress of P u r e and Applied Chemis t ry (1963).

a n d t h e n p l a c e d in a f u r n a c e u n t i l f u s i o n o c c u r r e d . T h e iTiol ten s a m p l e s w e r e a i r - q u e n c h e d a n d t h e n s l o w l y c o o l e d to r o o m t e m p e r a t u r e . T h e t e s t s a m p l e s i n t h e f o r m of r i g h t c y l i n d e r s -were p r e p a r e d by g r i n d i n g f l a t t h e e n d s of t h e s a m p l e i n g o t s .

T h e e l e c t r i c a l r e s i s t i v i t y a n d S e e b e c k v o l t a g e s ' w e r e m e a s u r e d o v e r a t e m p e r a t u r e r a n g e . T h e u p p e r t e m p e r a t u r e l i m i t of 3 73°K w a s s e t a t a r e a s o n a b l e i n t e r v a l b e l o w t h e s o f t e n i n g t e m p e r a t u r e s of t h e s a m p l e s . R e -s i s t i v i t i e s of 10 o h m s t o 10 o h m s v / e r e m e a s u r e d w i t h a n e l e c t r o m e t e r . A l t e r n a t i n g , r a t h e r t h a n d i r e c t , c u r r e n t w a s e m p l o y e d b e l o w 10 o h m s . S e e b e c k v o l t a g e s w e r e t a k e n u n d e r s t e a d y - s t a t e c o n d i t i o n s w i t h c o n s t a n t s a m p l e e n d t e m p e r a t u r e d i f f e r e n t i a l s of 5 . 5 - 2 4 . 7 ° C . T h e t h e r m a l v o l t a g e w a s b a l a n c e d a g a i n s t t h e o u t p u t of a p r e c i s i o n p o t e n t i o m e t e r b y u s e of a h i g h - r e s i s t a n c e s e r i e s - n u l l d e t e c t o r .

T h e t h e r m a l c o n d u c t i v i t y m e a s u r e m e n t s w e r e p e r f o r m e d w i t h a n a p p a r a t u s b a s e d u p o n t h e c o m p a r a t i v e s t e a d y - s t a t e m e t h o d of o p e r a t i o n s . V a l u e s Avere d e t e r m i n e d n e a r r o o m t e m p e r a t u r e .

S a m p l e c o m p o s i t i o n s w e r e p r e p a r e d a n d t e s t e d in t h e A s 2 T e 3 - A s 2 S e 3 -T l 2 T e a n d A s 2 T e 3 - S b 2 T e 3 - T l 2 S e s y s t e m s ( s e e F i g u r e 2 0 ) .

Figure 20. Compositional Diagram for System Studies

AsgTe, SbgTeg A s ^ ^ AS^SBJ

T h e a m o r p h o u s o r n e a r - a m o r p h o u s s a m p l e s u^e re A , G, a n d H of t h e l e f t d i a g r a m a n d B , C , D , F , G , a n d 1 t h r o u g h 7 i n t h e r i g h t d i a g r a m . T h e c r i t e r i a f o r c o n s i d e r i n g a m a t e r i a l t o b e a m o r p h o u s in s t r u c t u r e u ^ e r e :

a. Exh ib i t i on of concho ida l f r a c t u r e .

b . A b s e n c e of s t r u c t u r a l p e a k s in the X - r a y p a t t e r n .

37

Al l the a m o r p h o u s m a t e r i a l s exh ib i t ed an exponen t i a l v a r i a t i o n of r e s i s t i v i t y wi th t e m p e r a t u r e , and a n e g a t i v e t e m p e r a t u r e coeff ic ient of r e -s i s t i v i t y . A l though the S e e b e c k coef f ic ien t t e m p e r a t u r e da t a for the v a r i o u s s a m p l e s show s o m e s c a t t e r , s t r a i g h t - l i n e r e p r e s e n t a t i o n i s p o s s i b l e , ^ ^

The i n t e r e s t i n g f e a t u r e of the r e s i s t i v i t y v e r s u s c o m p o s i t i o n i s the d e c r e a s e in r e s i s t i v i t y a s s e l e n i u m r e p l a c e s sul fur , t e l l u r i u m r e p l a c e s

s e l e n i u m , and t h a l l i u m r e p l a c e s a r -

Figure 21. Correlation of Electrical Resistivity and Seebeck Coefficient

0 2 4 6 8 10 12 14 Log R e s i s t i v i t y P

s e n i c . It inay be s t a t ed tha t i s o -m o r p h o u s r e p l a c e m e n t -with e l e m e n t s f r o m h i g h e r p e r i o d s of the p e r i o d i c t a b l e wi l l c a u s e m o r e m e t a l l i c and l e s s a m o r p h o u s s t ab i l i t y condi t ions to e x i s t .

F i g u r e 21 i n d i c a t e s tha t e l e c -t r i c a l r e s i s t i v i t y a p p e a r s to be d i -r e c t l y p r o p o r t i o n a l to the S e e b e c k coeff ic ient . The a m o r p h o u s s a m p l e s of both s y s t e m s a r e c o n s i d e r e d . T h e r e f o r e , r e s i s t i v