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Reported twinning and dislocations in gadolinium metal thin films identified as occuring in b-type gadolinium sesquioxide crystals
Volume 32A, number 5
I?HYSICS L E T T E R S
10 August 1970
REPORTED TWINNING AND DISLOCATIONS IN GADOLINIUM METAL THIN FILMS IDENTIFIED IN B-TYPE GADOLINIUM SESQUIOXIDE CRYSTALS AS OCCURING C. B O U L E S T E I X , B. PARDO, L. VALIERGUE Inst~tut d'Opt$que, Facult~ des Sciences, 91 Orsay, France
and P. E. CARO, M. GASGNIER and C. H. La BLANCHETAIS Laboratoire des T e r r e s Rares du C . N . R . S . , 92 Bellevue, France
Received 29 June 1970
Twinning and dislocations reported in gadohnmm metal thin films by Smvastava, Kumar and Sllcox. are shown to be occurmg, m fact. m crystals of B-type gadohnmm sesqulox~de (monochmc).
S e v a r a l p a p e r s have been p u b l i s h e d r e c e n t l y on thin f i l m s of r a r e e a r t h m e t a l s i n v e s t i g a t e d by e l e c t r o n m i c r o s c o p y and diffraction. Two of t h e s e [1,2] d e s c r i b e twinning and d i s l o c a t i o n s in ga do l i n i u m , a n o t h e r one [3] d e s c r i b e d a new h. c . p . p h a s e of s a m a r i u m m e t a l . We have shown p r e v i o u s l y that the s a m a r i u m h. c . p . p h a s e was indeed B - t y p e S m 2 0 3 , [4]. The photographies presented here are from B-type Gd203 thin f i l m s , a m a t e r i a l analogous to B - S m 2 0 3. They show e x a c tl y the s a m e type of twinning and d i s l o c a t i o n s as r e p o r t e d f o r g a d o l i n i u m m e t a l and in r e f e r e n c e s [1] and [2]. The
oxide thin f i l m s a r e made by oxidizing at low t e m p e r a t u r e (300°C) r a r e ear t h m e t a l thin f i l m s into C - t y p e (b. c. c. ) Ln203 (Ln = r a r e earth). The r a r e e a r t h m e t a l s a r e v e r y e a s i l y o x i d i z e d in a dynamic v a c u u m c i r c a 10 -5 t o r r (and consequently d i r e c t l y in the e l e c t r o n m i c r o s c o p e under the e l e c t r o n b e a m impact). The C - t y p e oxide r e c r y s t a l l i z e s into the high t e m p e r a t u r e p h ase A-(hexagonal) o r B - ( m o n o c h n i c ) type o x i des, u n d er the e l e c t r o n b e a m impact. The s e v e r a l p h a s e s exhibited by the r a r e e a r t h oxides v e r s u s t e m p e r a t u r e and a t o m i c n u m b e r a r e d e s c r l b e d in s e v e r a l p a p e r s (see f o r instance [5]).
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Fig. 1. Electron diffraction pattern of a crystal of B-Gd203.
F~g. 2. Dlslocatmns m B-Gd203 (×30 000). 361
Volume 32A, number 5
PHYSICS LETTERS
10August 1970
O
Fig. 3. Twin bands m B-Gd20 3 (x30000). The plane of the A - t y p e L n 2 0 3 thin h l m s is p e r p e n d i c u l a r to the C - h e x a g o n a l axis, the plane of the B - t y p e L n 2 0 3 thin h l m s is p a r a l l e l to the (201) plane of the m o n o c l i n i c s t r u c t u r e . In both c a s e s the plane of the f i l m s is p a r a l l e l to the (LnO) n+ c o m p l e x c a t i o n i c group b a s a l plane. A and B - L n 2 0 3 have s t r u c t u r e s v e r y c l o s e l y r e l a te d and a r e b e s t f o r m u l a t e d (LnO)2 O, [6]. The B - t y p e exhibit twinning along p l a n e s {313} and {111} s p e c i a l l y . S t r u c t u r e and twinning in B - L n 2 0 3 thin f i l m s a r e r e p o r t e d m d e t a i l s e l s e w h e r e [7]. Fig. 1, shows the a l m o s t hexagonal 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 of a c r y s t a l of B - G d 2 0 3. The e l e c t r o m c b e a m is along the [10i] d i r e c t i o n , 3.5 ° off the p e r p e n d i c u l a r to the plane of the film ( p a r a l l e l to (201)). Fig. 2, exhibits d i s l o c a t i o n s at high c o n t r a s t and d i s l o c a t m n s nets at low c o n t r a s t . Fig. 3, r e p r e s e n t s {111} twin bands and fig. 4, the c o r r e s p o n d i n g 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 . V e r y s i m i l a r p i c t u r e s a r e to be found in r e f e r e n c e s [1] and [2].
362
F~g.4. Eleet~on dlftractton pattern for twin in fig. 3 B e c a u s e of the s p e c i a l i n t e r e s t of the d e f e c t s o b s e r v e d as pointed by S r i v a s t a v a [1], [2], we think that it is of p r i m e i m p o r t a n c e to r e c o g n i z e the r e a l n a t u r e of the m a t e r i a l involved which in o u r opinion is definitely m o n o c l i m c B type s e s quioxlde.
References [1] O.N Srlvastava and J Kumar, Phys Letters 27A (1968) 675 [2J O. N. Snvastava and J. Sllcox, Phil. Mag., 18 (1968) 503 [3] J. Kumar and O. N. Srlvastava, Acta Cryst.. B25 (1969) 2654. [4] C.Boulestmx, P . E . C a r o , M.Gasgmel, C.H. La Blanchetals, P.Pardo and L Vahergue, Acta Cryst., to be pubhshed. [51 M. Foex and J . P . T r a v e r s e , Rev. Int. Hautes Temper. et Refract., 3 (1966} 429. [61 P. E. Cara, J. Less Common Metals, 16 (1968) 367. [7] C.Boulestmx, P . E . C a r o , M.Gasgmer, C . H . L a Blanchetam and B.Pardo, Acta Cryst., to be pubhshed.
I?HYSICS L E T T E R S
10 August 1970
REPORTED TWINNING AND DISLOCATIONS IN GADOLINIUM METAL THIN FILMS IDENTIFIED IN B-TYPE GADOLINIUM SESQUIOXIDE CRYSTALS AS OCCURING C. B O U L E S T E I X , B. PARDO, L. VALIERGUE Inst~tut d'Opt$que, Facult~ des Sciences, 91 Orsay, France
and P. E. CARO, M. GASGNIER and C. H. La BLANCHETAIS Laboratoire des T e r r e s Rares du C . N . R . S . , 92 Bellevue, France
Received 29 June 1970
Twinning and dislocations reported in gadohnmm metal thin films by Smvastava, Kumar and Sllcox. are shown to be occurmg, m fact. m crystals of B-type gadohnmm sesqulox~de (monochmc).
S e v a r a l p a p e r s have been p u b l i s h e d r e c e n t l y on thin f i l m s of r a r e e a r t h m e t a l s i n v e s t i g a t e d by e l e c t r o n m i c r o s c o p y and diffraction. Two of t h e s e [1,2] d e s c r i b e twinning and d i s l o c a t i o n s in ga do l i n i u m , a n o t h e r one [3] d e s c r i b e d a new h. c . p . p h a s e of s a m a r i u m m e t a l . We have shown p r e v i o u s l y that the s a m a r i u m h. c . p . p h a s e was indeed B - t y p e S m 2 0 3 , [4]. The photographies presented here are from B-type Gd203 thin f i l m s , a m a t e r i a l analogous to B - S m 2 0 3. They show e x a c tl y the s a m e type of twinning and d i s l o c a t i o n s as r e p o r t e d f o r g a d o l i n i u m m e t a l and in r e f e r e n c e s [1] and [2]. The
oxide thin f i l m s a r e made by oxidizing at low t e m p e r a t u r e (300°C) r a r e ear t h m e t a l thin f i l m s into C - t y p e (b. c. c. ) Ln203 (Ln = r a r e earth). The r a r e e a r t h m e t a l s a r e v e r y e a s i l y o x i d i z e d in a dynamic v a c u u m c i r c a 10 -5 t o r r (and consequently d i r e c t l y in the e l e c t r o n m i c r o s c o p e under the e l e c t r o n b e a m impact). The C - t y p e oxide r e c r y s t a l l i z e s into the high t e m p e r a t u r e p h ase A-(hexagonal) o r B - ( m o n o c h n i c ) type o x i des, u n d er the e l e c t r o n b e a m impact. The s e v e r a l p h a s e s exhibited by the r a r e e a r t h oxides v e r s u s t e m p e r a t u r e and a t o m i c n u m b e r a r e d e s c r l b e d in s e v e r a l p a p e r s (see f o r instance [5]).
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Fig. 1. Electron diffraction pattern of a crystal of B-Gd203.
F~g. 2. Dlslocatmns m B-Gd203 (×30 000). 361
Volume 32A, number 5
PHYSICS LETTERS
10August 1970
O
Fig. 3. Twin bands m B-Gd20 3 (x30000). The plane of the A - t y p e L n 2 0 3 thin h l m s is p e r p e n d i c u l a r to the C - h e x a g o n a l axis, the plane of the B - t y p e L n 2 0 3 thin h l m s is p a r a l l e l to the (201) plane of the m o n o c l i n i c s t r u c t u r e . In both c a s e s the plane of the f i l m s is p a r a l l e l to the (LnO) n+ c o m p l e x c a t i o n i c group b a s a l plane. A and B - L n 2 0 3 have s t r u c t u r e s v e r y c l o s e l y r e l a te d and a r e b e s t f o r m u l a t e d (LnO)2 O, [6]. The B - t y p e exhibit twinning along p l a n e s {313} and {111} s p e c i a l l y . S t r u c t u r e and twinning in B - L n 2 0 3 thin f i l m s a r e r e p o r t e d m d e t a i l s e l s e w h e r e [7]. Fig. 1, shows the a l m o s t hexagonal 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 of a c r y s t a l of B - G d 2 0 3. The e l e c t r o m c b e a m is along the [10i] d i r e c t i o n , 3.5 ° off the p e r p e n d i c u l a r to the plane of the film ( p a r a l l e l to (201)). Fig. 2, exhibits d i s l o c a t i o n s at high c o n t r a s t and d i s l o c a t m n s nets at low c o n t r a s t . Fig. 3, r e p r e s e n t s {111} twin bands and fig. 4, the c o r r e s p o n d i n g 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 . V e r y s i m i l a r p i c t u r e s a r e to be found in r e f e r e n c e s [1] and [2].
362
F~g.4. Eleet~on dlftractton pattern for twin in fig. 3 B e c a u s e of the s p e c i a l i n t e r e s t of the d e f e c t s o b s e r v e d as pointed by S r i v a s t a v a [1], [2], we think that it is of p r i m e i m p o r t a n c e to r e c o g n i z e the r e a l n a t u r e of the m a t e r i a l involved which in o u r opinion is definitely m o n o c l i m c B type s e s quioxlde.
References [1] O.N Srlvastava and J Kumar, Phys Letters 27A (1968) 675 [2J O. N. Snvastava and J. Sllcox, Phil. Mag., 18 (1968) 503 [3] J. Kumar and O. N. Srlvastava, Acta Cryst.. B25 (1969) 2654. [4] C.Boulestmx, P . E . C a r o , M.Gasgmel, C.H. La Blanchetals, P.Pardo and L Vahergue, Acta Cryst., to be pubhshed. [51 M. Foex and J . P . T r a v e r s e , Rev. Int. Hautes Temper. et Refract., 3 (1966} 429. [61 P. E. Cara, J. Less Common Metals, 16 (1968) 367. [7] C.Boulestmx, P . E . C a r o , M.Gasgmer, C . H . L a Blanchetam and B.Pardo, Acta Cryst., to be pubhshed.