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LA-lJR -85-242

LA-UR--85-242

DE85 006712

TITLE SHIFTED HOMOLOGOUSRELATIONSHIPS BETWEEN THE TRANSPLUTONIUM ANDEARLY RARE-5ARTH METALS

.,:.,,;... ,.. P: ‘.,,. ? k-i,{,. . . .. . . . A:. .. .. ---- ,.... . . ---,.. .AUTHOR(S): John W. Ward

SUBMITTEDTO Symposium cn Americium and Curium Chemistry and Technology.PAC-Chem. Conference, Honolulu, HI, December 1984.

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——, —

LosAumilos LosAlamos NationalLaboratorLosAlamos,New Mexico 8754 ~

! OnM NO 130 m------- . . .

SHIFTED HOMOLOGOUSRELATIONSHIPS BETWEEN

THE T’RANSPLUTONIUMAND EARLY WRE-EARTH METALS*

.?ohn W. Ward

Materials Science and Technology Division

Los Alamoe N~tional Laboratory, Los Alarnos, NM 87544

ABSTMCT

The phyaico-chemical properties of the late actinidemetals americium through ●insteinium arp compared with theirrare-earth counterpart. Localization of the 5f ●lectronsbeginning at amerl~ium signals the appe~rance of true rare-earth-like properties, but the homologous relationship is●hifted to place americium below pr~s~odpium, ein~teiniumthen below ●uropium. The comparison of crystal structure,phase transitions, vapor pressures and heats of vaporiza-tion reveals remarkable similarities, ●specially for Sm-Cfand Eu-Es, where the stability of the divalent met~l be-comes ●stablished ●nd divalent chamietry then follows.

There 10 of coursa a major perturbation at the half-filled shell ● t curium, ●nd it may be argued that ●mericiumia the anomaly in the so-called second rare-earth eeries.However, the res:onse of americium, berkellum and caltfoynfumunder pressure revealn the true perturbation to be a thermo-dynamic ~ne, occurring at curium.

The onset of 5f cloctron localization in the ●ctinides i~ probably

first seen in the hiuher temperature phases nf plutonium, pa-titularly

the fcc d~lta phase, with ● matallic radius of 1.64~ and a rare-earth-

like X-ray ●dsorption-cmiesion rasponaa.’ Nevertheless, no magnetism is

ohnerv~d, ●nd th? radiuo is ntill cmall cnparad to the rare-earth

metals. 5f bonding rcturnm with ●vmnRance in the epmilon and liquid

phases, producing (as with ntptunium) ● vary 10V ❑elting point and a

litq~ld with ●xtramely high viecomitv ●nd hiRh boiling point,

ThQ mystery continuos with amaricium, whera ● major localization

●nd f-band narrowing occurs but magnetism lo ●gain quenched by the

“mn~ic” 5f6 electronic configuration; this peculiar non-magnetic

gro$jnd-etate •l~c) allown amaricium to become superconducting, like

~w~r~~d perfo~ed under th~ au~pic.n of the [!,s, Department of ~nergv

2

le,~thanum.2 Chemically americium 12 clearly a trivhlent metel. The

divalent state ie only stabilized by a large ligand such ae l-;

tetravalency occurs with strong oxidizing agents (O~,F2) because the 5f

●lectrons, though localized, are very close (<2cV) to the Fermi level.

Crystal structures are like those of the ●arly rare-earths - dhcp l,t

ioom temperature and fcc at higher temperatures. High-pressures3

transfonu the lattice first to an fcc atrucsur: (as do the rnre-earths>,

then to an ●xotic double body-centered monocli~ic phase, and then

finally te an a-uranium-type structure in the range 15-20 GPa, again

showing the pr~ximity of the 5f ●lectrons co the Fermi level..

The dhcp room temperature and fcc. high temperatures art also found

for cerium, and also the elements berkelium and californ:um, in marked

conLrast to the supposed homologs directly above these ●lements in cha

periodic table. A sugge~tion first noted by Johansson4 ~hifcs the

homoloRoua relationship to place mmericium below praaeodvmium, then

comparfng the two ●eriae as chemical ●nd structural humlogo. This

comparison ie illustrated in Table 1. T“lm f-bondad ●arly ●c:inide~ ar-

grouped for convenience under plutonium, which becomes the homolog for

(the f-bonded collapsed ~-pl,nse ofl cerlum. It should be noted that

cerium 18 often used ae a ●tf,nd-in for plutonium, where radioactive

contamination must be avoided.

Americium then b~comes the homolog for praseodymium, as noted

nbcve. Both metals can he oxidized to the dioxide, due to the pro~imic~

of the f-energies to ~he Fermi lev?l. 1 heat of vnporj~tion fcr Pr =

85.0 kcal/mol my be comparwl with 67.9 kctil/mol for @-, as mea~ured by241

Ward and coworkere (5,6) an both the AM and 243 h isotopes: these

dat~ ● re ehown in ?18. 1, A long-.etanding controversy be?waen the

weaeured and theoretical valuas fcr the haat af vaporization has recent-

ly been roeolved by ● new spect~oocopic value for the loweet level of

the f6de2 Am I confi~ration, thue finally brinRing cht theoretical

calculations into harmonv with ●xperiment. Various thaoret~ca! treat-

.entaL,7-lohave had coaeid?rable ●uccese in predicting the coh~eive

tn~rgiee (wheat of vaporization) for the rare-earths, failing for the earlv

●ctinidem becauee of no viable model for the itiverant ●nd bondinp

3

5f-electrons. These correlations are based orl the spectroscopic values

for the gas and the heat of solution; it ❑ight therefore be expected

that reasonable estimates would be made for the elements americium and

beyond, where f-bonding no longer iB in the picture. This indeed turns

out to be true, with the resolution of the americium calculation just

discussed.

It can be seen immediately that a major perturbation in the homo-

logous relationship in Table 1 occurs at curium, becallse of the half-

filled shell effect. Is curium like neodymium or gadclinium? Crvstal-

structure-wise the former is true; in terms of a heat of vaporization

(Q “ 92.2 kral/molp ~ - 95.0 kcal/mol-, Nd = 73.3 kcal/mol) the latter

seems to bc true. However, the “problem” is not really a problem at

all; Lhe argument is simply R thermodvnarnlc one, since the half-filled

shell :tabilizes the trivalent Cnr(Gd) gas. In terms of solid-state—— .

properties, the homologous relationship remains Cm-Nd.

For the elements beyond plutonium, meamrements of the heat cspac-

Ity Fire difficult-to-lmpoeslble, due to the Intense radioactivity andlor

vanishinglv-small quantities for ●xperiment. Ward and Hill” havd

established a correlation relating th~ crvstal ●ntrnpv S0~9R to metallic

radius, atomic weight) magnetic properties and ●~.ectronic structure.

This correlation permits ●stimation of reliable entropy valueu for

❑~tals for which no data are available, based on comparison with a

closely-siruilar metal for vhlc}l there ●re measured data. The early

actinides cannot b~ assessed by this correlation, because there is no

model (aa for the thoormtical calculation) to account for the complex

5f-electron bondlrlg. However, success is ●xpected and realized for the

metala americium and beyond, The ●atimatec’ value for the correlation

for ●mericium of 13.2 cal,/mol/K has been precisely confirmed recently

by ●xperiments on the243

Am isotope.12

Noteworthy IS the hugh changa of entropy (4,13 cal/K/mol) upon

vaporization of Am from the trivnlent non-magnetic nolid to the divalent

magnetic gas. It should be noted that all of the actinide gases t?re

fully magnetic, like the rare-aarths, as shown ~n Fig. 2. Perhaps this

ohould be obvious) but interastfng is the fact that simple subtraction

4

of the magnetic entropies results in a good non-magnetic baseline,

●xcept for curium, where there aze many low-lying excited states.

The importance of the crystal entropy lies in the fact that the

‘i98value ie the basis point for the free-energy functlone for both the

solid and gas. From a reasonably accurate ●stimate for the eolid

entropy, the gaseous apectroacopic data and precise va?or pressure

❑easurements, It IS possible to calculate all the thermodynamic func-

tions for the ❑etal up to the highest temperatures of measurement.

These values have been recently tabulated in the Metals Chapter of the

“Handbook for the Physic~ and Chemistry of the Acrinides”.13

Unfortunately there exist as yet ‘n; data for the rare-earth element

promethium, so a comparison with berkelium cannot ●asily be made,

However, it ISI expected on the basis of the regularity eeen elsewhere

that the comparison will be ●xcellent. In ~he measurement of the vapor14

pressure of pure berkelium-249 metal neodymfum wag uged as the comp~r-

ative ●lement for the entropy correlation, correcting of course for the

proper magnetic ●ntropies, ●nd the fit was ●xcellent. The measured heat

of vaporization of 74.1 kcal/mol may be compared with that for neodymium

of 78.3 kcal/mol, with the ●xpectation that the the value for promethium,

when finallv measured, will be lower.

The comparison at samarium/californium is especially revealing.

Incipient ~tabilization of the divalant state is seen in both metals,

with d~valent chemical compounds ●asily fonaed. The surface of samarium15

metal has been shown to be divalent , and there was some quegtion in

the ●arly stages of californlum metal #tudies whether the metal was16

divalent, However, the themnodynamic data clearly ●stablfeh

californium to be a trivalent metal but with a heat of vaporization of

only 46.9 kcal/mol (as cnmpared to 49.4 kcal/mol for ●amarium) ard with

a vapor pressure midway between that for samarium ●nd ●uropium, ●s shown

in Fig. 3.

Recent tlenrv’e-Law vaporization otudie~ of ●inateinium-253 disgolved

~.n ytterbium show9’ ‘7 the metal to be clearlv divalent, with a heat of

vaporization of only 31.8 kcal/mol fuimilar to strontium), thus

completing the homologous minieerie~ by analogv to divalent europium,

5

Some comparative properties of the early lanthanides and late

actinides are summarized in Table 2. Trends in cohesive enerRies are

Illustrated by the meaeured heats of vaporization of the actinide

metals, plotted in Fig. 4.

Beyond ●insteinium there 16 no correspondin~ half-filled shell in

the actinide Berie6, and the divalent ntate will continue to be the

preferred ●lectronic configuration for the metals fermium and beyond.

At the moment, half-lives are too 6hort and quantities too small for

meaningful bulk meamrement6 beyond ●insteinium.

Thus in summary, a shifted homologou6 relationship ,:xigtg for the.

transplutonll :n actinide6, resultin~ in the miniseries Ar,I-5s cnrrespondiny——

to the series Pr-Eu. The half-filled ehell at Q introduces a thermo-

dynamic complication which is however not reflected jn the conden~ed

phase properties of this ●lement.

REFERENCES

1. Ronnelle, C., Structure and Bonding (Berlin) ~ (1976) 23.

2. Smith, J. L., Haire, P. C., Science ZOO (1978) 535.

3. Roof, R. B., Zeit. fur Krietall, 158 (1982) 307.

4. Johanason, B., Phvs. Rev. B ~ (1975) 2836.

5. Wardp J. W., ?ltiller, W., Kramer, G. ~., Transplutonium 197S, Eds W.Pluller end R. Lindner, North-Holland, Amsterdsm/American Elsevier,New York (1976) 161.

G. \fard, J. W., Kleinechmidt, P. D., J. hem. Phy~. 711 (1979) 3920,

7. Nugent, L., Burnet:, J. L., Mores, L. A.1 J. Chem. Thermo~ j (1973)665.

8. Sanhoun, K., Ph.D. Thesisp Univereite”de Paris-Sud, Centre d’Orsay,Ser. A, No. 1727, 1976.

9. Kleinachmidt, P. D,, Ward, J. W., Hatlack, G. M., HaIre, P. G., HjRhTemperature Sclcnce (1984) - to be published.

10, Johanaaon, B., J. Leee-Comnonn lletale (1984) - to be publinhed.

6

11. Ward, J. W., Hill, H. H., Heavv Element ?ro~ertles, Eds. W. Muller& H. Blank, North-Hollalld,—h-ste~dam/American Elsevier, !iew York(1976) 65.

12. Muller W,, Schenkel, L., Schmidt, H. E., Spirlet, J. C,, McE!roy,D. L., Hall, R. O. A., Mortimer, M. J., J. Low-Temp. Phys. 30, 561.—

13. Ward, J. W., Kleinschmidt, P. D., Peterson, D. E., Chapter“Thermochemical Properties of the Actinide Elements and SelectedActinide-Noble Metal Intermetallics,” in the Handbook of thePhysics and Chemistry of the Aciilides, Eds. A. J. Freeman, G. Landerand C. Keller, North-Holland, Amsterdam (1984) - to be published.

14. Ward, J. W., Kleinschmidt, P. D., HaIre, R. G., J, Chem. Phys. 77(1982) 1464,

—--

15. Allen, J. W., Johansson, L., Ba*~er, R. S., Lindau, I., Hagstrom,S. B. A., Phys. Rev. Let, Q (1978) 1499.

16. Ward, J. W., Kleinschmidt, P. D., Haire, R. G., J. de Phvsique(Paris) 40 (1979) C4-233.—

17. Kleinschmidt, P. D,, Ward, J, W., Matlack, G. M., Haire, R, G., J.Chem. Phys. 81 (1984) 473 .

COWARATIVE PHYSl~HEMISITtY OF LANTHANIDES AND ACTINIDES(THE “JOHANSSON SHIFT”)

t--.

la1lce~ ~ Pr Nd Pm WI LEu* W IIJ

; II hdf-fillecl shell1I

rxl L

Am yll WI Cf Es* CL —-

{ ------- ------ ------ ----- r

hdf-fi!!d shall \

“df-tlondhlg

9

Table 2. Comparative Values for the Actinides Am-Es and Lanthanides Pr-Eu

Hetal Crystal H.P. B. P. c* S;q*v

Pair(s) Phases——h dbcp, fCC

(K)

mii(298K) (Cal/K/Hoi) (Cal/K/mol)—.. —.+2220 5.97 13.20

Pr dhcp, fcc 1204 3785

Cm dhcp, fCC 1618 3383

Nd dhcp, fcc “ 1289 3341(cd) (hCP, bee) (1585) (3539)

Bk dhcp, fcc 1323 2900m dhcp, fee(?) +1350 2730(?)

Cf dhcp, fcc 1173 1745* U-SM (dhcp u.n- 1345 2064

der pressure)

Es fcc 1?33 1261Eu bcc 1090 1870

[ ] = other possible valence states

●frm che Entrnpy correlation, Uard S Hill (11)

6.56

63

(:.0:)

6.24=

b.70a

7.06

6.3986.48

17.67

17.20a16.99

(16.24)

18.68a

19.25a16.61

21.38a

19.31

@cal/Hoi)6~9—85.0

92.273.3

(95.0)

74.1?

46.949.4

31.841.9

I

Chemistry

1Iul~v ]III [IV)

IIT (Iv]111 [Iv](111)

111111

Ill, 11111, 11

1111

7

.Figure Captions

1. Vapor pressure data for americium. The heavier line represents 37data points taken with the 241 isotope (Ref. 5); ●xtent of range isindicated by small arrovs. Data points and the lighter linerepresent values with the 243 ieotope, extending into the liquidranRe: OLOS Alamos data; ● Karleruhe data (Ref. 6).

2. Comparison of flaseous ●ntropies for the lanthanides and actinides at29BK and 1400K. o: divalent (d”) curve for the lanth~nides; .trivalent (d’) gases; 9 fullv magnetic actinide gas;~non-magneticportion of entropy for each element.

3. Vapor pressure of solid californium, compared to data for samariumand europium (Ref. 16).

‘arget ‘a-m 0 and m=28B:;t;::;;:; :::avere taken, stately with a 2 ❑g sample of purethe highest points was due to incipient sample depletion).

4. Comparative plot of the cohesive energies of the actinide metals, inkJ/mol (left ordinate) or kcaltmol (right ordinate). Open datapoint at & represents a still-unresolved uncertainty for thiselement.

1#

T, 1 1 l“’’]’’ ’’1’ ’’’1 ’’’’1’’” l“’’1” ’’’1”’

\ r-p-y 1345~

n b,l,.,11.!lli,llli)i, 1 ,1,,1,,,,1,,,,1,41

0.6 0,7 0,0 0.0 1.0IOOCVT(KWIN)

mom

o-0*

cn-

,-

58 ‘ I I I I 1 I I T I 1 1 I I }

57 r Vpa VCm*d’

‘1.d vu

56 VNP ● d’ -VW 4

55

54

53-

,d’

t

151 -

u●+:-WV”’

50 * wAm(u)

49 “Non-mag” baseline (4f)H = A+++=a———” — 4

“r—’——— ‘ I 1 h’ I I 1 I I

48 --

;P

c47 au

NP.

d’46

Ce TtI ~. ~45 t

‘b,

44 - 65 )●d’

43 -

42 ‘~-v- ---

—

40 LO Ce Pr Nd Pm Sm Eu Gd T’b Dy Ho Er Tm Yb h

——

s—— . . . ..-. — — —.-. —.—— -

I04

i

\ -4

I 0-7

I

\ .

\

\

\

\

Sm\

\

\

AH:=-45.28kcal/mole\

AS; =25.97 e.u. \

0- TARGET DATA \O- MASS SPEC. DATA

\.-

\

\ 1

~10-8&“’’L-’’’’’’’’’’’’’’’’’’’’’’” “’’’”f

0.9 I●o 1.1 i .2 13

IC)OO/T(keMn)

600

500

400

30C

20C

10(

I 4 I I I I I I I I

.

.

M(s,l) to M(g)

.

I I I I 1 1 1 I i I

Th u Pu Cm CfPa Np Am Bk Es

60

40

20

100

80

60

40

20