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Low temperature XRD study of actinide metals and compounds
U. Benedict, C. Dufour, K. Mayne
To cite this version:
U. Benedict, C. Dufour, K. Mayne. Low temperature XRD study of actinide metals and compounds.
Journal de Physique Colloques, 1979, 40 (C4), pp.C4-103-C4-105. �10.1051/jphyscol:1979432�. �jpa-
00218828�
JOURNAL DE PHYSIQUE Colloque C4, supplément au ri> 4, Tome 40, avril 1979, page C4-103
Low temperature XRD study of actinide metals and compounds
U . B e n e d i c t , C . D u f o u r a n d K . M a y n e (*)
Commission of the European Communities, Joint Research Centre, European Institute for Transuranium Elements, Postfach 22 66, D-7500 Karlsruhe 1, F.R.G.
Résumé. — La variation du paramètre de réseau entre 50 et 300 K a été mesurée pour Th, Pa, PaC, UC, PuC, PuN et Pu(C, N). Aucune transformation de phase ou anomalie n'a été observée dans ce domaine de températures. Les coefficients de dilatation linéaire ont été déterminés à partir des courbes a{T). Ils sont proches de zéro pour UC, PuC et PuN entre 50 et 100 K. Le volume de la maille de Pa décroît puis augmente si ce métal est refroidi de 300 à 50 K.
Abstract. — The low temperature lattice parameter variation was measured for Th, Pa, PaC, UC, PuC, PuN, and Pu(C, N). No phase transformation or anomaly was observed in the range 50 to 300 K. The coefficients of thermal linear expansion were deduced from the a(T) curves. For UC, PuC, and PuN, the expansion coefficient is close to zero between 50 and 100 K. The unit cell volume of Pa first decreases then increases on cooling from 300 to 50 K.
1. Introduction. — S o m e actinide metals and c o m p o u n d s w e r e studied on a low t e m p e r a t u r e X- r a y diffractometer -equipped with a closed-cycle helium cooling d e v i c e . Particular a t t e n t i o n w a s paid t o metals a n d c o m p o u n d s for w h i c h anomalies in physical p r o p e r t i e s s u c h as t h e r m a l e x p a n s i o n , elec- trical resistivity, and magnetic susceptibility h a d b e e n o b s e r v e d a t low t e m p e r a t u r e .
2. Experimental. — 2.1 MATERIAL. — T h e m a t e - rials studied w e r e :
— thorium a n d protactinium metal p r e p a r e d b y t h e r m a l dissociation of t h e iodides o n a r a d i o f r e q u e n c y - h e a t e d t u n g s t e n s p h e r e [1],
— protactinium monocarbide o b t a i n e d by car- b o t h e r m i c r e d u c t i o n of P a205 [2], [3] ; this s a m p l e still contained a large a m o u n t of g r a p h i t e ,
— uranium monocarbide p r e p a r e d f r o m t h e melt b y N U K E M ( 4 . 7 2 % C , 0 . 0 4 % O , 0 . 0 6 % N ) ,
— plutonium monocarbide of c o m p o s i t i o n P u C0 7 9N0 0 1 5O0 0 2 5D0 1 7 ( • = non-metal lattice v a c a n - cies) p r e p a r e d by c a r b o t h e r m i c r e d u c t i o n of P u 02 [4],
— plutonium mononitride of c o m p o s i t i o n P u N0 JJC,, 0 2O0 01 p r e p a r e d b y c a r b o t h e r m i c r e d u c t i o n of P u Oz in t h e p r e s e n c e of nitrogen [4],
— plutonium monocarbonitri.de p r e p a r e d b y sin- tering t h e t w o p r e c e d i n g p r o d u c t s together [4].
2.2 A P P A R A T U S A N D M E T H O D . — T h e e x p a n -
der t u b e of a closed-cycle cryogenic s y s t e m w a s m o u n t e d into a n e v a c u a t e d c a m e r a with beryllium w i n d o w s w h i c h fitted o n t o an X-ray dif-
f r a c t o m e t e r [5]. A thin layer of t h e p o w d e r e d s a m p l e w a s fixed o n t h e end-plate of t h e e x p a n d e r t u b e ; t e m p e r a t u r e w a s m e a s u r e d b y a Au-0.07 % F e / c h r o m e l t h e r m o c o u p l e inserted into a radial b o r e of this e n d - p l a t e . Details of t h e m e t h o d a r e given e l s e w h e r e [4], [5].
3. Results and discussion. — Figures 1 , 2 , a n d 3 s h o w t h e variation of t h e lattice p a r a m e t e r s b e t w e e n 50 K a n d t e m p e r a t u r e s slightly a b o v e r o o m t e m p e r a - t u r e . A n a n o m a l y indicating p h a s e t r a n s f o r m a t i o n s or o t h e r t r a n s f o r m a t i o n s w a s not d e t e c t e d in this t e m p e r a t u r e r a n g e . I n particular, t h e a n o m a l y in t h e r m a l e x p a n s i o n previously r e p o r t e d for P u C b e t w e e n 80 a n d 100 K on t h e basis of strain gauge m e a s u r e m e n t s [6] w a s n o t confirmed b y t h e p r e s e n t w o r k . P r o t a c t i n i u m k e p t its tetragonal s t r u c t u r e
Fig. 1. — Lattice parameter variation for UC, PuC, PuN, and Pu(C, N).
(*) University of Surrey, Guildford, Surrey, England.
8
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979432
C4-104 U. BENEDICT, C. DUFOUR AND K. MAYNE down to 55 K ; the variation of slope of resistivity
observed for this metal at about 100 K [7], [8] is thus not connected to a change in crystallographic struc- ture.
Fig. 2. -Lattice parameter variation for PaC and Th.
Fig. 3. - Variation of lattice parameters and unit cell volume V for Pa.
The thermal linear expansion AL/L,, and, whe- rever possible, the coefficient of thermal linear expansion were calculated from the lattice parame- ters. Figure 4 shows the alignment of the present data with the recommended curve for thermal linear expansion at T > 293 K [9] and the variation of the expansion coefficient between 50 and 350 K for plutonium monocarbide. Similar curves were obtain- ed for PUN, UC, and Pu(C, N), but for Th (Fig. 5),
-1.0
100 200 T,,K 300 400
-=
9.9,(%I
PuC aZg3= 4,3702
T K
Fig. 4. - Thermal linear expansion and instantaneous coefficient of thermal linear expansion for PuC.
Fig. 5. -Thermal linear expansion for Th.
the present results indicate an approximately linear variation of AL /L, below 293 K.
The expansion coefficients are the instanta- neous coefficients a, = (a,
-
~,)/[u,,~(T, - T,)], a, and a , being the lattice parameters at T, and TI, resp., where T , = T ,+
20 ; they are valid at T,,, = ( T I+
T2)/2. a t , a,, and a,, were read from the lattice parameter versus temperature curve. For the following materials, only the mean coefficient of thermal linear expansion for the range 60-293 K was determined :PaC, am = 3.9 X ~ o - ~ K - ' ;
Th, am = 11.9 x K-' ; Pa//c, am = 3.4 x lop6 K-'
.
It is noteworthy that for UC, PuC, and PUN, the lattice parameter contraction becomes very small below 100 K. It is of the order of the accuracy of the measurement, and thus makes the a = f ( T ) curves appear horizontal in the range 50 to 100 K. For the actinide dioxides, Marples [lo] observed a similarly small lattice parameter variation for this temperature range. This leveling off cannot be due to plutonium self-heating as it is also observed for UC. It is not observed for the f .c.c. metal Th (Figs. 2 and 5) nor for most of the common cubic metals.
We determined the instantaneous expansion coef- ficients from Marples' lattice parameter curves for the oxides and observed that the a , = f (T) curve for PuO, is practically congruent with that for PuC shown in figure 4. The thermal expansion behaviour of these two compounds is thus very similar between 50 and 293 K.
For Pa, the c parameter slightly decreases with decreasing temperature. The measured values for the a parameter are best fitted by a second degree function which increases when cooling between 150 and 50 K. The volume of the unit cell calculated from the a ( T ) and c(T) functions first decreases, then increases on cooling.
LOW TEMPERATURE XRD STUDY OF ACTINIDE METALS AND COMPOUNDS
References [I] SPIRLET, J. C., J. Physique Colloq. 40 (1979) C4-87.
121 BOHET, J., EUR 5882 (1977).
[3] BOHET, J., MULLER, W., J. Less -Common Metals 57 (1978) 185.
[4] BENEDICT, U., DUFOUR, C., SCHOLTEN, O., J. Nucl. Mater.
73 (1978) 208.
[5] BENEDICT, U., CORNAY, Y., DUFOUR, C., paper presented at the 27th annual X-ray conference Applications o f X-ray analysis, Denver/Colorado, Aug. 1-4, 1978 ; to be pu- blished in Advances in X - r a y analysis, Vol 22.
[6] JACQUEMIN, J., CEA-R-4386 (1973).
[7] HALL, R. O., LEE, J. A., MORTIMER, M. J., J. LOW Temp.
Phys. 27 (1977) 305.
[8] BETT, R. (Eur. Inst. Transuranium Elements), personal communication (1977).
[9] TOULOUKIAN, Y. S., KIRBY, R. K., TAYLOR, R. E., DESAI, P. D., LEE, T. Y. R., Thermal Expansion, Vols. 12 and 13 of Thermophysical Properties of Matter (IFI/Plenum, New York-Washington) 1975 and 1977.
[lo] MARPLES, J. A. C., in : Plutonium 1975 and other Actinides, edited b y H. Blank and R. Lindner (North Holland/American Elsevier, New York) 1976, p. 353.