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High resolution neutron diffraction study of α-uranium
J. Fournier, A. Delapalme, C. Zeyen, G. Lander
To cite this version:
J. Fournier, A. Delapalme, C. Zeyen, G. Lander. High resolution neutron diffraction study of α-uranium. Journal de Physique Colloques, 1979, 40 (C4), pp.C4-136-C4-137.
�10.1051/jphyscol:1979443�. �jpa-00218839�
JOURNAL DE PHYSIQUE Colloque C4, supplément au n° 4, Tome 40, avril 1979, page C4-136
High resolution neutron diffraction study of a-uranium
J. M . F o u r n i e r , A . D e l a p a l m e , C . Z e y e n (*) a n d G. H . L a n d e r (**)
Centre d'Etudes Nucleaires de Grenoble, Departement de Recherche Fondamentale, 85 X, 38041 Grenoble Cedex, France (*) Institut Laue-Langevin, BP 156, Centre de Tri, 38042 Grenoble Cedex, France
(**) Argonne National Laboratory, Argonne, Illinois 60439, U.S.A.
Résumé. — Des mesures précises de diffraction élastique de neutrons ont été menées à I.L.L. pour mettre en évidence le long des directions (faOO), (OfcO), (00/) des distorsions périodiques du réseau associées à de possibles ondes de densité de charge (C.D.W.) au-dessous de 43 K ; le résultat est négatif. Nous avons mesuré pour la première fois les variations de paramètres cristallins liées à la transition du 1" ordre à 37 K
Abstract. — We have performed at I.L.L. a high resolution neutron diffraction study of a - U . The search along (hOO), (OfeO) and (00/) directions, for periodic lattice distortions associated with a possible charge-density wave (C.D.W.) below 43 K has been negative. We have measured for the first time the first order transition at 37 K and found :
1. Introduction. — A n u m b e r of u n u s u a l effects h a v e b e e n o b s e r v e d at = 43 K in a - u r a n i u m over t h e last 15 y e a r s [1]. A l t h o u g h m o s t of t h e electronic p r o p e r t i e s (e.g. susceptibility) s h o w only small ef- f e c t s c o m p a r e d w i t h t h e a n o m a l i e s in elastic c o n s t a n t s and t h e r m a l e x p a n s i o n , t h e 43 K transi- tion is a s s u m e d t o b e electronic in n a t u r e . S i n c e t h e biggest effect o c c u r s for elastic c o n s t a n t s , l o w t e m - p e r a t u r e p h o n o n m e a s u r e m e n t s [2] w e r e carried out a t O . R . N . L . a n d I . L . L . a n d s h o w t h a t t h e p h o n o n intensities is r e d u c e d substantially at this t e m p e r a t u - r e w i t h smaller effects in t h e line w i d t h . T h e c h a n g e in intensity p r e s u m a b l y reflects a d e c r e a s e in t h e vibrational a m p l i t u d e , w h i c h m a y b e related t o chan- g e s in t h e i n t e r a t o m i c f o r c e s b e l o w t h e transition.
Crystallographic investigations with b o t h X- r a y s [3] a n d n e u t r o n s [ 3 , 4 ] failed t o find a n y e v i d e n - ce for a t r u e p h a s e transition a n d lend further s u p p o r t t o t h e idea of a subtle electronic transition.
D u r i n g t h e c o u r s e of our p h o n o n e x p e r i m e n t s at I . L . L . , w e also p e r f o r m e d e x t e n s i v e elastic q scan a b o u t (200) p o i n t , t o s e a r c h for a possible charge- d e n s i t y w a v e .
I n this p a p e r , w e r e p o r t n e g a t i v e conclusion a b o u t this point a n d reinvestigations of results given by p r e v i o u s w o r k s [ 3 , 4] with p r e c i s e d e t e r m i n a t i o n of t h e first o r d e r transitions a t 37 K .
2 . Experimental and results. — T h e single crystal u s e d w a s a b o u t 3 x 8 x 4.4 m m along t h e a, b a n d c
d i r e c t i o n s . E x p e r i m e n t s w e r e d o n e on D 1 0 at I . L . L . , with a n e u t r o n w a v e l e n g t h , A = 1.262 A ; t h e e x p e r i m e n t a l A / 2 contribution w a s a b o u t 4 x l 0 ~4. I n s c a n s along [/i00], w e h a d 13 x 106
c o u n t s (counting time = 5 m i n . ) o n t h e (200) reflec- tion with a flat b a c k g r o u n d , 150 ± 4 0 . W e could t h e r e f o r e d e t e c t v e r y easily definite signals e q u a l t o t h e b a c k g r o u n d , w h i c h m e a n s w e h a d a 10"5 preci- sion with r e s p e c t t h e strongest reflections of this a - u r a n i u m crystal (width of reflection : 12').
a) F i r s t w e l o o k e d t o find a n y p e a k s at low t e m p e r a t u r e a r o u n d t h e (200) reflection. Profiles w e r e p e r f o r m e d at 30 K , 43 K a n d 60 K , a n d w e could n o t find a n y e v i d e n c e for small p e a k s at qx = 0 . 1 1 r.l.u. ; t h e profiles w e r e t h e s a m e inside an e r r o r b a r of 5 x 10"6 times t h e strongest reflections.
b) A p r e c i s e c h e c k of t h e p a r a m e t e r - t e m p e r a t u r e d e p e n d e n c e w a s carried out b e t w e e n 26 K a n d 65 K . W e s e e easily t h e 43 K s e c o n d o r d e r transition a n d clearly (Fig. 1) t h e 37 K first o r d e r transition on t h e A0a j u m p . T h i s c h a n g e in t h e (400), (080) a n d (006) position at t h e transition t e m p e r a t u r e gives t h e relative c h a n g e in t h e crystallographic p a r a m e t e r s :
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979443
HIGH RESOLUTION NEUTRON DIFFRACTION STUDY OF a-URANIUM C4-137
Fig. 1. - Bragg angle-temperature dependence for (400), (080) Fig. 2. -Integrated intensities versus temperature for (400),
and (006) reflections. (080) and (006) reflections.
2
Figure 2 shows the evolution of integrated intensi- It is seen from the examination of figures 1 and 2 ties in this temperature interval and confirms pre- that the change in integrated intensity
-
probably vious results on peak intensities [4], where the chan- related to extinction phenomena-
is more con- ge in intensity is more pronounced for the (400) and nected with the first order transition at 37 K than (006) reflections than for the (080) one. with the second order transition at 43 K.References Bragg angle
-.
*-<_ *u (0 06)
*..-.*..
8 - . * 8 8
d o -e , 0 - ~ ,
.W 0 - 0 0 - 0
.o-- W0---O
(0 8 0)
,-%-*. a-
-=..
*-
?B'
.
i
( 4 0 0 )
//
Ae=0.lo
[I] SMITH, T. I?., FISHER, E. S . , J. LOW Temp. Phys. 12 (1973) 631.
[2] FOURNIER, J . M., DELAPALME, A., LANDER, G. H., PYNN, R., WAKABASHI, A. N., NICKLOW, R. M., D. C. Meeting of the American Physical Society (1978).
[3] BARRETT, C. S . , MUELLER, M. H., HITTERMAN, R. L., Phys.
Rev. 129 (1963) 625.
[4] LANDER, G. H., MUELLER, M. H., Acta. Crystallogr. B 26 (1970) 129.
intensity
( 0 0 6 )
-%. . .
0.
. . ;..-
--- 0 0
0 rn
0 4 0 , n , + - - o D -o._--- 0 0
( 0 8 0 )
( 4 0 0 )
