8/3/2019 M. Madon, J. Peyronneau and J.P. Poirier- Diamond Anvil Cell= Shock Wave Gun?

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J O U R N A L , D E P H Y S I Q U EC o l l o q u e C 8 , s u p p l e m e n t a u n l l , T o m e t5 , n o v e m b r e 1 9 84 p a g e C 8 - 1 1 7

DIAMOND ANVIL CELL = SHOCK WAVE GUN ?M. M a do n, J . P e y r o n n e a u a nd J . P . P o i r i e rInstitut de Physique du Globe, University Pierre et Marie Curie, 4, P laceJussieu, 75230 Paris Cedex OS, France

Ab st rac t - T r a n s m i s s io n e l e c t r o n m i c ro s c op e o b s e r v a t i o n s o f o l i v i n e(M g j Fe ^ S i O , , d e fo rm ed i n a l a s e r -h e a te d d i a m o n d -a n v i l h i g h p re s s u re c e l l r e v e a l t h a tt h i s d e v i c e c re a te s d e fo rm a t i o n c o n d i t i o n s s i m i l a r t o t h o s e p rod u c ed b y s ho ck wa v es .

The a ( o l i v i n e ) , (3 ( "m o d i f i e d " s p i n e l ) and y ( s p i n e l ) p o ly m o rph s o f a c o m p o s i t i o n c l o s e to th e m a g ne s ia n e nd o f (M g j Fe ^ S i GV a re e s s e n t i a l m i n e r a l s o f t h eE a r th ' s u p p e r m a n t l e [ 1 , 2 ] , p e r o v s k i t e ( M g , F e ) S i 0 3 and ma gne s iow us t i te (Mg ,Fe)0p ro b a b l y b e i n g m a j o r c o n s t i t u e n t s o f t h e l o we r m a n t l e [ 3 , 4 ] . The p has e t r a n s i t i o n sb e twe e n th e se m i n e ra l s a re t h e o b j e c t o f s u s ta i n e d i n te re s t [ 5 ,6 ] an d o ne o f t h em ost p r o m i s i n g l i n e s o f i n v e s t i g a t i o n c o n s i s t s i n u s i n g t r a n s m i s s i o n e l e c t r o nm i c ro s c o p y (TEM ) and e l e c t r o n d i f f r a c t i o n a n a l y s i s t o ex am in e h i g h p re s s u re p h as ess y n t h e s iz e d i n t h e l a b o r a t o r y [ 7 , 8 ] o r r e s u l t i n g fro m n a t u r a l p r oc e ss e s [ 9 , 1 0 ] .I n t h i s p a p e r , we p re s e n t t h e r e s u l t s o f TEM o b s e rv a t i o n s o f o l i v i n e b ro u g h tto pr es su re s between 50 and 70 GPa and te m pe ra tur es between 1000 and 2000 C in al a s e r - h e a t e d d i a m o n d - a n v i l c e l l .1 - SAMPLES

The s t a r t i n g m a t e r i a l was n a t u r a l San C a r l o s o l i v i n e (M g 0 _ 8 8 , F e 0 _ 1 2 ) 2 s i 0 1 ( w i t h0 .5 % o f f i n e l y p o wd ered c a rbo n to f a c i l i t a t e a b s o rp t i o n o f t h e l a s e r be am . Thepowdered m ix tu re was imbedded in t he ho le (250 \m d i a m e t e r) o f a s t a i n l e s s s t e e lgasket (200 \im th ic k ) and the sample was brou ght to pre ss ure s between 50 and 70GPa. Press ures were measured by the s t r a i n gauge tec hn iqu e de sc r ib ed by Peyronneau 4a l . i n t h i s j o u r n a l . The s a m pl es we re th e n r a i s e d to t e m p e ra tu re s b e twe e nap prox ima te l y 1000 C (es t im a te d f rom the b r ig h t ne ss o f th e samp le ) and 2000 C(e s t i m a te d u s i n g th e m e l t i n g p o i n t o f o l i v i n e u nd er p re s s u re ) b y s c a n n i n g a c ro s s t h esample a la se r beam focused on a 30 pm d iam ete r sp o t . The quench pro duc ts were g lu edon copper gr id s and ion-beam th in n e d . The t h in edges o f th e ho le s were then examinedin a P h i l ip s EM 300 e l e c tr o n micro scop e at 100 Kev and in a Jeo l 2000 EX at 200 Kev.2 - TEM OBSERVATIONS

Whatever the p ress u re app l i ed on the samp les , on ly two type s o f t ex tu re s a reo b s e rv e d a c c o rd i n g to t h e te m p e ra tu re o f t h e e x p e r i m e n t :i ) The f i r s t typ e o f te x t u r e i s ob ta ine d a t " l ow " tempe ra tu re (T1000 C) andc o n s i s t s i n am orph ou s z on es w i t h i n c r y s t a l l i n e r e g i o n s o f f i n e l y sh e ar ed o l i v i n e( F i g . 1 ) . The d i f f r a c t i o n p a t t e r n c o r re s p o n d in g t o c r y s t a l l i n e r e g i o n s i s t h e samea l l ove r the samp le and shows the o l i v in e p a t te rn w i th a second pa t t e r n super imposedon i t t h a t was i n de x e d a c c o r d in g t o t h e s p i n e l s t r u c t u r e ( F i g . 1 - a ) . The o r i e n t a t i o nr e l a t i o n s h i p J je tw e e n t h e tw o p a t t e r n s - ( 1 0 0 ) o l p a r a l l e l t o ( 1 1 1 )s p and 0 0 l ] o lp a r a l l e l t o [ l 1 0 ] s p ( F i g . 1 - b ) - i s c o m p a t i b l e w i t h a m od el r e c e n t l y p ro p os e d [ 1 0 , 1 1 ]o f an o l i v i n e - s p i n e l s he ar t r a n s i t i o n e f f e c t e d by t h e m o t io n o f p a r t i a l d i s l o c a t i o n s

R s in - L ' o b s e r v a t i o n e n m i c r o s c o p i e l e c t r o n i q u e p a r t r a n s m i s s i o n d ' o l i v i n e(Mg jFe ^S iO , , d fo rme dans une c e l l u le enc lumes de d iaman t c hau f fe pa r l a se rm o n t re q ue c e t a p p a re i l l a g e c r e de s c o n d i t i o n s d e d fo rm a t i o n s e m b l a b l e s c e l l e sp rodu i tes pa r des ondes de choc .

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984823

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F ig . 1 .- a ) D i f f r a c t i o n p a t t e r n o f c r y s t a l l i n e r e g i o n s s ho w in g t h e p r e s e n c e o f tw os t r u c t u r e s : o l i v i n e and s p i n e l . -b) O r i e n t a t i o n r e l a t i o n s h i p b e tw e en t h e two s t r u c -t u r e s . - c ) a nd - d ) TEM i m a g es s h ow i n g g l a s s y z o n e s ( g ) b e tw e e n c r y s t a l l i n e r e g i o n s .on t h e c l o s e p acked p l a n e s o f tw o s t r u c t u r e s . The o r i e n t a t i o n r e l a t i o n s h i p be tw e ent h e two p h a s e s is n o t v i s i b l e o n TEM i m a g es ( F ig . 1 - c an d d ) b u t we c a n s u p p o s e t h a tt h e tw o p h a s es a r e v e ry f i n e l y i n t e r c a l a t e d and p ro du ce t h i s s h e a r ed s t r u c t u r e . Thea mo rp ho us z o n es a r e s e e n b et we en c r y s t a l l i n e r e g i o n s a s p a t c h e s w i t h b l u r r e do u t l i n e s ( Fi g. 1- c) o r f i n e l a n e l l a e a lo n g c r y s t a l l o g r a p h i c p l a n e s o f t h e h o s tc r y s t a l (Fig.1-d) .

T h e s a n e t e x t u r e o f a morpho us z o n es w i th i n c r y s t a l l i n e r e g i o n s o f f i n e l ys h e a r e d o l i v i n e ( F ig . 1 - c ) h a s b ee n o b s e rv e d i n o l i v i n e d e fo rm e d by s h o c k w av es a t 56GPa [12 ] . I f we u s e t h e c a l c u l a t i o n o f s h oc k t e m p e r a t u r e s m ea su re d i n s h o ck e ds i n g l e - c r y s t a l M g2Si04 [ 1 3 ] , we o b t a i n a t e m p e r a t u r e o f 1 0 00 O C a t 56 G Pa, a s i n o u re x p e r i m e n t s .

i i ) The se co nd t y p e o f t e x t u r e i s o b t a i n e d a t h i g h t e m p e r a t u r e (T =2 00 0 O C)a f t e r o l i v i n e b r e a k s down t o an a s s em b la g e o f ( 4 , F e ) O p l u s ( M g, Fe )5 i0 3 g l a s s( F ig . 2 ) . The e l e c t r o n d i f f r a c t i o n p a t t e r n s a l lo w t h e i d e n t i f i c a t i o n o f c r y s t a l l i n ep h a s e r n a g n e s i o w i j s t i t e (M g,Fe)O a n d sh ow t h e p r e s e n c e o f a n o r p h o u s z o n e s ( h a l o i nd i f f r a c t i o n p a t t e r n s ) e x p e c t e d t o b e ( W j, Fe )S iO , g l a s s ( F i g . 2 -a ) . TEM i m a g es sh ow- t h e h e t e ro g e n e ou s t e x t u r e o f c r y s t a l s and g l a s s : t h e (Mg,Fe)O c r y s t a l s a r e e lo n g a t e d( F i g .2 - b ) o r m o re o r l ess m i c r o c r y s t a l l i n e (F ig .2 -c and d ) w h e r ea s g l a s s y z o n e sa p p e a r a s s n o o t h a r e a s ( F ig . 2 - b ) o r p o l y g o n a l " g r a i n s1 ' ( F i g .2 - d ) . In s i t u X -raym i c r o a n a l y s i s c o n f i r m s t h a t g l a s s h a s t h e c a n p o s i t i o n ( Mg ;F e)S i0 3 and t h a t i r o nd i s p r o p o r t i o n a t e s b et we en (N g ,F e)O a nd (Mg , F e ) S i Q 3 , g o i n g p r e f e r e n t i a l l y t om a g n e s i o w i i s t i t e :

T h i s s t r o n g Fe-% a r t i t i o n i n g be tw e en t h e tw o p h a s e s h a s a l r e a d y b e en o b se r v ed byX - r a y d i f f r a c t i o n {14] .

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F i g . 2.- a) E l e c t r o n d i f f r a c t i o n p a t t e r n o f m a g n e s i o w u s t it e . -b ) , - c ) a n d - d ) TEMi ma ge s s ho win g d i f f e r e n t t e x t u r e s o f c r y s t a l s (Mq ,Fe)O a d g l a s s (Mg , F e ) S i 0 3 .The t e x t u r e c o n s i s t i n g o f ( b , F e ) O c r y s t a l s and ( b , F e ) S i 0 3 g l a s s h as a l s ob e e n o b s e r v e d i n o l i v i n e d e f o r m e d by s h o c k w a ve s b e t w e e n 78 and 92 GPa [1 5] . Fo rt h e s e p r e s s u r e s , t h e c a l c u l a t i o n [ 1 3 ] g i v e s a t e m p e r a t u r e b et we en 1800 a d 2 200 O Cc o m p a t i b l e w i t h o u r e x p e r i m e n t a l c o n d i t i o n s .

3 - DISCUSSIONThe e x p e r i m e n t a l o b s e r v a t i o n s r a i s e s e v e r a l p r ob le m s t h a t we w i l l n o w d i s c u s s .i ) I n " lo w" t e m p e r a t u r e e x p e r i m e n t s b e tw e e n 50 an d 7 0 G Pa, i . e . i n t h es t a b i l i t y f i e l d o f p e r o v s k i t e a nd r na g ne s i ow i is t i te , we o b s e r ve t h e l e s s s t a b l e

y - s p i n e l . Now, o l i v i n e c a n t ra n s f o r m t o y - s p i n e l by a s h e a r o f t h e ox yg en s u b l a t t i c eand a s h u f f l i n g o f t h e c a t i o n s [ l l ] , a me ch an is m t h a t d o e s n o t d em an d h i g ht e m p e r a t u r e s and ca n b e he l p ed by s h e a r s t r e s s e s ; t h e t r a n s f o r m a t i o n o f y - s p i n e l t op e r o v s k i t e and m a g n e s i o w ii s ti t e, on t h e o t h e r h a nd , p r e s u n a b l y i n v o l v e s d i f f u s i o n ,h en ce c a n o t t a k e p la c e i f t h e t em p e r a t u r e is n o t h i g h e n o u g h . A t h i g h p r e s s u r e s a ndlo w t e m p e r a t u r e s , o l i v i n e m ig ht t h e r e f o r e t r an s fo r m i n t o y - s p i n e l , a m ore s t a b l e ,a l t h o u g h n o t t h e mo st s t a b l e p h as e , b e c au s e t h e e n e r gy b a r r i e r is m u ch l o w er t h anf o r t r a n s f o r m i n g t o p e r o v s k i t e a nd m a g n e s io w u s t i t e . I n o u r e x p e r i m e n t s , as w e l l a si n s ho c k waves e x p e r i m e n t s [ 1 2 ] , g l a s s was l o c a l l y o b s e r v e d . T h e re i s a p o s s i b i l i t yt h a t h i g h l y d efo rm ed o l i v l n e m i gh t l o c a l l y t r an s fo r m t o g l a s s , p e rh a ps b e ca u se av e r y h i g h d i s l o c a t i o n d e n s i t y m ak es t h e t r a n s f o r m a t io n t o g l a s s k i n e t i c a l l y e a s i e rt h m t h e t r a n s f o rm a t io n t o s p i n e l .i i ) I n " hi gh " t e m p e r a t u r e e x p e r i m e n t s , i r o n - r i c h m a g n e si o w u st i t e is f ou nd a se x p e c t e d b u t t h e ( M g , F e ) S i 0 3 p h a s e i s a g l a s s i n s t e a d o f t h e e x p e ct e d c r y s t a l s w it hp e r o v s k i t e s t r u c t u r e . The swe o c c u r r e n c e h a s b e en o b s er v e d i n s w p l e s r e c o v e r e d

f ro m sh o c k wave e x p e r i m e n t s [ 1 5 ] b u t a l s o i n s t a t i c e x p e r i m e n t s on Ca S i0 3 [ 1 6 , 1 7 ]w he re a p e r o v s k i t e - s t r u c t u r e p h as e h a s been i d e n t i f i e d i n - s i t u a t h ig h p r e s s u re ,a l t h o u g h t h e r e c o v e r e d s a m p l e s w e re g l a s s y , p re su m a bl y d ue t o a r e t r o g r e s s i v e

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t ran sfo rma tion during the rel eas e o f pressure. We have not been able so far toascertain whether the (Mg ,Fe)SiOg phase i n our experiments i s c r y s ta l l in e under hig hpressure, nor i s i t obvi ousl y po ss ib le to know whether i t i s the case fo r recoveredshock sanples. Two hyp oth es is may th er ef or e be cons idere d (bo th f o r th e dianonda n v i l and the shock wave experiments):- a) The o l i v i n e i s f i r s t tak en t o hi g h p re s-s ur es , w e l l i n t o the s t a b i l i t y f i e l d o f perov-sk i t e , before be ing heated. There i s the refo re 1bbq1-a considerab le anount o f energy sto red i n the - h,so.system, o f the order o f l o 5 J / mole (Fig.3). T.~SOO'