X-RAY DIFFRACTION TECHNIQUES IN THE DIAMOND ANVIL HIGH PRESSURE CELL

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X-RAY DIFFRACTION TECHNIQUES IN THE DIAMOND ANVIL HIGH PRESSURE CELL

I. Spain

To cite this version:

I. Spain. X-RAY DIFFRACTION TECHNIQUES IN THE DIAMOND ANVIL HIGH PRESSURE CELL. Journal de Physique Colloques, 1984, 45 (C8), pp.C8-395-C8-397. �10.1051/jphyscol:1984870�.

�jpa-00224372�

JOURNAL DE PHYSIQUE

Colloque C8, supplément au n ° l l , Tome 45, novembre 1984 page C8-395

X-RAY DIFFRACTION TECHNIQUES IN THE DIAMOND ANVIL HIGH PRESSURE CELL

I.L. Spain

Department of Physios, Colorado State University, Fort Collins, Colorado 80523, U.S.A.

Résumé - Les techniques expérimentales applicables à la diffraction X dans les dispositifs à enclumes de diamant, sont examinées. La compa- raison (a) de la dispersion d'énergie avec la dispersion angulaire et (b) des expériences en rayonnement synchrotron avec les sources conven- tionnelles sera faite. Les techniques expérimentales basse température

(%10-300 K) seront aussi discutées.

Abstract - Experimental techniques for x-ray diffraction in the diamond anvil high pressure cell will be discussed. A comparison (a) of energy dispersive and angle dispersive and (b) of synchrotron and conventional source experiments will be made. Techniques for experiments at low tem- perature (1-10-300 K) are also discussed.

I - INTRODUCTION

A brief review of methods used by us for x-ray diffraction experiments with the diamond anvil cell will be given. This includes the use of both conventional and synchrotron radiation, and experiments at low temperature. The brevity of the paper allows only conclusions to be given and mainly references from our own work.

Discussion will be limited to powdered samples.

II - X-RAY DIFFRACTION USING SYNCHROTRON RADIATION

The arrangement used by us for energy-dispersive x-ray diffraction (EDXRD) measure- ments using synchrotron radiation is illustrated in Fig. 1, and is similar to that used by other researchers /1,2/ with some differences. The main problems which are encountered in using this brilliant energy source of wide energy range are:

(1) The beam is narrow in the vertical direction, so that precise positioning of the diamond cell is mandatory. This has been achieved by us through the use of an on-line detector, with the diamond cell mounted in a carriage whose position can be adjusted and monitored to ±20 urn (see later). (2) A collimator is needed to direct the incident x-rays onto the sample, avoiding the gasket. A two-slit collimator has allowed the adjustment time to be kept to a minimum (approximately a few minutes) which is important, since beam time is valuable, and the beam height varies rapidly during set-up, and can drift slowly during an experiment /3/.

Detector slit / C Z ^ > V

\

Vs~- - ^ - Sol id state

" J \.

beam [IIP ~rfS VL S ^ K ' ' " " ' \ " ^

\ \ ( ^ ^ n T ^ r l ^ ^ ~ j Noise reducing On-line

\ ^ M I — \C^^ slit proportional

t ^ ^ \ ^ counter Al filter X-Y-Z stage

Incident beam collimators

Fig- 1 - Sketch of the energy-dispersive x-ray diffraction arrangement using synchrotron radiation.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984870

C8-396 JOURNAL DE PHYSIQUE

(3) I t i s v e r y i m p o r t a n t t o r e d u c e d e t e c t o r c o u n t s from s p u r i o u s s o u r c e s a s much a s p o s s i b l e . An A 1 f i l t e r and t h e diamond a n v i l s r e d u c e low e n e r g y photons, w h i l e s h i e l d i n g and a d o u b l e s l i t system o n t h e d e t e c t o r r e d u c e high-energy c o u n t s . Even when background n o i s e i s reduced a s much a s p o s s i b l e , t h e d e t e c t o r , and more i m p o r t a n t l y t h e d e t e c t o r e l e c t r o n i c s , c a n b e o v e r l o a d e d . It was e s t i m a t e d d u r i n g r e c e n t r u n s a t CHESS t h a t d a t a c o u l d have been d e t e c t e d a p p r o x i m a t e l y 1 0 t i m e s f a s t e r i f d e t e c t o r e l e c t r o n i c s c o u l d be improved, and a p p r o x i m a t e l y 1 0 0 t i m e s f a s t e r i f b o t h d e t e c t o r and e l e c t r o n i c s c o u l d be improved s u f f i c i e n t l y . During t h e s e e x p e r i m e n t s t h e s o l i d a n g l e subtended by t h e d e t e c t o r s l i t was %2-3

s t e r a d i a n s , whereas a v a l u e of %2

10-4 s t e r a d i a n s c o u l d have been a r r a n g e d w i t h o u t l o s s of measurement p r e c i s i o n .

A p r e l i m i n a r y e x p e r i m e n t h a s been c a r r i e d o u t t o t e s t whether a c r y s t a l d e t e c t o r c o u l d b e u s e d t o r e p l a c e t h e s o l i d s t a t e d e t e c t o r . C a l c u l a t i o n s show t h a t s u c h a n arrangement c o u l d g i v e h i g h e r s i g n a l - t o - n o i s e r a t i o and b e t t e r peak r e s o l u t i o n . The i d e a l arrangement i s one i n which b o t h a s o l i d s t a t e and a c r y s t a l d e t e c t o r a r e used, w i t h t h e l a t t e r programmed t o s e a r c h o n l y n e a r peak p o s i t i o n s .

Sample h e a t i n g c a n b e s e v e r e i n a diamond a n v i l c e l l i f t h e sample i s immersed i n a f l u i d s u c h a s a l c o h o l ( t h e r m a l c o n d u c t i v i t y 'l.0.15 W/mK). For i n s t a n c e , a temper- a t u r e r i s e of 10-50 K i s p o s s i b l e u s i n g t y p i c a l c o n d i t i o n s a t CHESS ( 5 GeV, 1 0 mA) 4 The h e a t i n g e f f e c t can b e p a r t i c u l a r l y s e v e r e a t low t e m p e r a t u r e (T

20

I11 - X-RAY DIFFRACTION USING CONVENTIONAL RADIATlON

A n g l e - d i s p e r s i v e x-ray d i f f r a c t i o n (ADXRD) h a s been c a r r i e d o u t w i t h

r a d i a t i o n u s i n g b o t h f i l m and p o s i t i o n s e n s i t i v e p r o p o r t i o n a l d e t e c t o r s . EDXRD h a s been c a r r i e d o u t u s i n g W-Bremsstrahlung and a S i ( L i ) d e t e c t o r . The PSPD i s g e n e r a l l y t h e p r e f e r r e d t e c h n i q u e g i v i n g a p p r o x i m a t e l y 10-20 t i m e s t h e c o u n t s i n d i f f r a c t i o n peaks f o r a g i v e n t i m e e x p o s u r e compared t o EDXRD, w h i l e s e n s i t i v i t i e s a r e com- p a r a b l e . A more d e t a i l e d comparison i s g i v e n e l s e w h e r e 151.

A comparison of EDXRD a t CHESS t o t h a t o n a c o n v e n t i o n a l s o u r c e shows t h e former t o g i v e a p p r o x i m a t e l y 5000 t i m e s t h e count r a t e . A c c o r d i n g l y ,

i s a n t i c i p a t e d t h a t ADXRD u s i n g a PSPD and a r o t a t i n g anode s o u r c e s h o u l d produce 'l.0.05 - 0 . 1 t i m e s t h e c o u n t r a t e i n d i f f r a c t i o n peaks compared t o CHESS. Apparatus f o r t h i s e x p e r i m e n t i s b e i n g s e t up.

I V - X-RAY DIFFRACTION EXPERIIIENTS AT LOW TENPERATURE

E a r l y e x p e r i m e n t s were c a r r i e d o u t by us i n s m a l l diamond c e l l s u s i n g a LHe-flow c r y o s t a t 161.

h a s been found more c o n v e n i e n t (300

T

1 0 K) t o u s e a n A i r P r o d u c t s D i s p l e x r e f r i g e r a t o r w i t h Mylar windows. The t e m p e r a t u r e of t h e sample can b e c o n t r o l l e d t o 20.2 K p r o v i d e d a p p r e c i a b l y h e a t i n g by t h e x-ray beam does n o t o c c u r .

I n e x p e r i m e n t s w i t h a c o n v e n t i o n a l s o u r c e of x - r a d i a t i o n , a p i n h o l e c o l l i m a t o r i s l o c a t e d behind t h e i n c i d e n t s i d e diamond a n v i l . The p i n h o l e d i a m e t e r i s u s u a l l y a p p r o x i m a t e l y t w o - t h i r d s t h a t of t h e g a s k e t h o l e , s o t h a t p r e c i s e p o s i t i o n i n g of t h e diamond c e l l i n t h e beam i s r e q u i r e d . For t h i s purpose, t h e c a r r i a g e d i s c u s s e d e a r l i e r h a s been m o d i f i e d t o p r o v i d e x-y-z l i n e a r a d j u s t m e n t s and a n g u l a r a d j u s t - ments ( i O . Z O ) a b o u t t h e

and y a x e s ( x - a x i s p a r a l l e l t o t h e beam).

P r e s s u r e measurement h a s been accomplished u s i n g N a C l o n C s C l x-ray s c a l e s . For t h i s p u r p o s e Decker's

e q u a t i o n o f s t a t e s c a l e s have been extended t o low temper- a t u r e 181.

V - DIAMOND ANVIL CELLS

Diamond a n v i l c e l l s have been m o d i f i e d and improved by u s o v e r a p e r i o d of t i m e

u s i n g t h e B a s s e t t c e l l

a s a b a s i s . M o d i f i c a t i o n s have i n c l u d e d t h e u s e of

t u n g s t e n c a r b i d e r o c k e r s / l o / , r o c k e r a d j u s t m e n t p l a t e s I l l / , t o u g h e r ,

Body

Rockers'

'

Diamonds and sample

\

Ball race Bellevilla spring washers

I

F i g . 2 - S k e t c h o f a diamond a n v i l c e l l u s e d f o r l o w - t e m p e r a t u r e m e a s u r e m e n t s . l o w - t e m p e r a t u r e a l l o y s 1 1 2 1 , p n e u m a t i c / h y d r a u l i c p i s t o n a c t i v a t o r s , improved c o l l i m a t o r s f o r e n h a n c e d r a d i a t i o n i n t e n s i t y .

E x p e r i m e n t s h a v e m o s t l y b e e n c a r r i e d o u t i n t h e r a n g e up t o 500 k b a r , w i t h some t o

%700 k b a r . U n t i l r e c e n t l y , 4 : l m e t h a n o 1 : e t h a n o l was u s e d as t h e p r e s s u r e t r a n s - m i t t i n g medium. L a t e r s t u d i e s w i t h Ar a s p r e s s u r e t r a n s m i t t i n g medium h a v e con- f i r m e d t h e i m p o r t a n c e o f t h e s t a t e o f stress c o n d i t i o n o n t h e d e t a i l s o f p h a s e t r a n s i t i o n s . F i g u r e 2 shows a c r o s s s e c t i o n o f a diamond a n v i l c e l l u s e d i n t h e r e f r i g e r a t o r .

ACKNOWLEDGEMENTS

Thanks a r e d u e t o NASA, Ames L a b o r a t o r y , f o r a g r a n t s u p p o r t i n g t h i s work (iiNAG2-157).

REFERENCES

BAUBLITZ I t . , ARNOLD V., RUOFF, A. L. , Rev. S c i . I n s t r . 52 (1981) 1 6 1 6 . SKELTON, E.F., QADRI, S.B., WEBB, A.W., LEE, C.W., KIRKLAND, J . P . , Rev. S c i . I n s t r . 56 (1983) 403.

SPAIN, I . L . , BLACK, D.R., MENONI, C.S., Rev. S c i . I n s t r . ( i n p r e s s ) . MENONI, C.S., SPAIN, I . L . , High Temp.-High P r e s s . 16 (1984) 1 5 7 .

SPAIN, I.

BLACK, D.R., MERKLE, L.D., HU, J . Z . , MENONI, C.S., P r o c e e d i n g s o f I n t e r n a t i o n a l Workshop o n X-ray D i f f r a c t i o n a t H i g h P r e s s u r e , K a r l s r u h e , West Germany, August 1984 ( t o b e p u b l i s h e d ) .

SKELTON, E.F., SPAIN, I . L . , YU, S.C., LIU, C.Y., CARPENTER, E.R., Rev. S c i . I n s t r . 48, (1977) 8 7 9 .

DECKER, D.L., J. Appl. P h y s . 42, (1971) 3239.

PIENONI, C.S., SPAIN, I . L . , High Temp.-High P r e s s . 16 (1984) 1 1 9 .

BASSETT, W.A., TAKAHASHI, T., STOOK, P.W., Rev. S c i . I n s t r . 38 (1967) 3 7 . SKELTON, E.F., LIU, C.Y., SPAIN, I . L . , Rev. S c i . I n s t r . 9 (1977) 1 9 . YU, S.C., LIU, C.Y., SPAIN, I . L . , SKELTON, E.F., "High P r e s s u r e S c i e n c e and T e c h n o l o g y , V o l . 1," p . 274 (1979) ( e d . K.

Timmerhaus a n d M. S. B a r b e r , Plenum P r e s s ) .

SPAIN, I . L . , SKELTON, E.F., RACHFORD,

"High P r e s s u r e S c i e n c e a n d Tech-

n o l o g y , V o l . 1," p . 1 5 0 (1980) ( e d . Vodar a n d M a r t e a u , Pergamon P r e s s ) .