AN INTERNAL FRICTION STUDY OF N-H AND O-H PAIRS IN SINGLE CRYSTAL OF NIOBIUM AT LOW TEMPERATURES

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AN INTERNAL FRICTION STUDY OF N-H AND O-H PAIRS IN SINGLE CRYSTAL OF NIOBIUM AT

LOW TEMPERATURES

R. Hanada, M. Shinohara, Y. Sado, H. Kimura

To cite this version:

R. Hanada, M. Shinohara, Y. Sado, H. Kimura. AN INTERNAL FRICTION STUDY OF N-H AND

O-H PAIRS IN SINGLE CRYSTAL OF NIOBIUM AT LOW TEMPERATURES. Journal de Physique

Colloques, 1981, 42 (C5), pp.C5-757-C5-761. �10.1051/jphyscol:19815117�. �jpa-00220986�

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JOURNAL DE P H Y S I Q U E

CoZZoque C 5 , suppi6ment au nOIO, Torrorrre 42, octobre 1981 page C5-757

AN INTERNAL FRICTION STUDY OF N-H AND 0-H PAIRS IN SINGLE CRYSTAL OF NIOBIUM AT LOW TEMPERATURES

R. Hanada, M. S h i n o h a r a , Y . Sado and H. Kimura

Research I n s t i t u t e for Iron, SteeZ und other metals, Tohoku University, Sendai, Japan.

Abstract.- A torsional internal friction measurement was ?erform- ed for Nb single crystals containing N - l i and 0 - H pairs at low tenperatures. A clear peak was found at 6OK for N-H and 50K for 0-Ii with the measuring frequency of 1 Hz. For N-H, the magnitude of the peak was found to depend on the orientation but the 2eak temperature does not. The result for N-H is analysed to show that fi occupies the third nearest octahedral site to iq. For 0 - H , the results are more complex than for N-H. The tenperature de- pendence of tile jump rate of Fi in a 0 - H pair is also discussed.

1. Introduction.- Properties of 0-ii or N-H pair in 14b have been exten- (1) ( 2 ) sively investigated with anelastic technique between 60K and 200K.

In these works, however, the internal friction measurements are limited above 60K and only the results of the strain relaxation experiments are present below 6SK. since thenon-classical jumping of H atoms (H jumping) is proposed to be observed in these tenperatures, a detailed study of the 0 - H or N - H pair below 60K is required to investigate the cause of their non-classical behavior.

In the ?resent pa?er, the results of a low frequency (-1 Hz) internal friction measurement on Nb sinele crystal containing N-1-1 or 0 - H pair is reported. The purposes of the experiments are (i) to study the structure of N-E or 0-ti pair and (ii) to examine the temperature de- pendence of the H jump rate around 0 or N below 60K. Also the results on polycrystals will be briefly summarized to identify the observed internal friction peak is due to the 0 - H or N-H pair.

2. Experimental.- Polycrystalline specimens of 0 . 5 m diameter and of Scm length were prepared from the Nb wire s u ~ p l i e d by MRC (Marz Grade).

The specimens were first annealed in an UHV to reduce the impurities concentration to less than 30 atppm. Subsequently _Nor 0 was doped by Sievert method to the concentration between 3.2 and 1 at%. The concentration was determined by a residual resistivity measurement at 4.2K with the resistivity contribution of N or 0 of 4 pcm/a%. Finally, H was electrolyticly charged to the specimens in a water bath kept at OeC with monitoring the H concentration by a resistivity measurement (ApOeC)

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19815117

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C5-758 JOURNAL DE PHYSIQUE

The resistivity contribution o f 3 . 7 uQ-cm/a% is assumed. The H-charged specimen was cooled to 4 . 2 K with the same rate as in the following q'' xeasurement and the resistivity increase (A2 ) due to H was also

4 . 2 X

measured at 4.2K. This is to examine whether 1-1 is trapped to N or 0 or precipitated at low temperatures.

Single crystals were s u y l i e d by F E I , of w:lich size are almost the sale as those o f polycrystals. The axial orientation of the single crystals were <loo>, <113>, and <Ill>. The orientations are reexamined by Laue method to show the stated orientations are correct within ^{* 3 O .} The methods of doping 0 , i i and H to the 0 - H or N - H specimens are almost the same as those for polycrystals.

Internal friction (Q-') was measured by a torsion pendulum type apparatus. The specimens was cooled to 10K at a rate o f 5 to 10 K/min and subsequently ^{Q - I} was measured during warm-up at a rate o f 3.1 to O.SK/min. The measuring frequency was between 3.2 to 2 Hz. The Q - ' value was obtained by measuring the duration with which the initial amplitude of the torsional oscillation (2x10-' s.s.s.) decays to 3/4.

The duration is typically 5 min for the back-ground and 2 to 3 min for the peak maximum.

3. liesults.

3-1. Polycrysta1s.- Fig. 1 shows a result o f Q - ' measurcnent on poly- crystal Nb. The peak at SOX is identified as due to 0-11 complex, since the peak is observed only in the specimen containing both 0 and M. No well defined peak is present neither in a high purity specimen with H - charging or in an 0 doped specinen without 11-charging.

Results o f ex?eriment to identify the kind of 0-I! comglex giving rise to the 50K peak may he sumsarized as follows. (i) The magnitude of the peak ( Q - I subtracted with the background) is proportional to the

;i concentration when it is less than that o f 0 . (ii.) Xnen the H concentration is larger than that o f 0, the magnitude of the peak tends to saturate to a constant. (iii) The ratio ( A p 4 e 2 K / A ~ D O C ) is about 0.7.

The results for i4-H arc alinost the same with tile 0-ti specimens.

These results can only b c explained that the 50K peak is due to simple 0-11 pairs consisting o f single t[ atom trapped to single 0 atom.

The peak temperature is so lov that the I [ concentration in a-phase is practically none and all H is bound to 0. Therefore, the concentration of 0 - H ?air is simply equal to [t:] when [I:]<[O]. Thus the result (i) is explained. lihcn [ H I is made to exceed 101, the extra H ([lil- [O]) 2recipitated and the concentration o f the pair is no\,, simply that of 0.

T h i s explains the (ii). The result (iii) is in agreement with tne oi)-

servation by Pfeiffer and liipf7(3) where they found that a simple N-ti

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p a i r i s f o r m e d a t low t e m p e r a t u r e when [N]>[!1]. From t h e s e we may c o n - c l u d e t h a t t h e S O X p e a k i s d u e t o t h e 0-11 > a i r a n d i t i s c a u s e d by t h e m i g r a t i o n o f H a r o u n d 0 . The s a n e a p p l i e s t o N - M c a s e .

3 - 2 . S i n g l e c r y s t a l s . - F i g . 2 a n d 3 shows t h e r e s u l t s on P!-H a n d 0-H, r e s p e c t i v e l y . I i e r e , t h e if c o n c c n t r a t i o n i s c o n t r o l l e d n o t t o e x c e e d t h a t o f 0 o r N a n d y e t a l m o s t t h e same f o r t h e t h r e e o r i e n t a t i o n s . The t e m p e r a t u r e s o f t h e N-M p e a k i s i n d e p e n d e n t o n t h e o r i e n t a t i o n a n d e s - s e n t i a l l y t h e same w i t h t h a t i n ~ o l y c r y s t a l s . However, i t s h o u l d be n o t e d t h a t t h e m a g n i t u d e o f t h e p e a k i s s t r o n g l y o r i e n t a t i o n d e p e n d e n t . I:or t h e a l m o s t t h e same I i c o n c e n t r a t i o n , i t i s h i g h e s t f o r

< l o o >

a n d t h e l o w e s t f o r . Almost t h e same t r e n d i s o b s e r v e d f o r 0-H p e a k s e x c e p t t h a t t h e p e a k t e m p e r a t u r e f o r i s a few d e g r e e h i g h e r t h a n t h a t o f

< l o o > .

The r e s u l t s i n F i g . 2 f o r N - f : may be a n a l y s e d a s f o l l o w s . The r e - l a x a t i o n s t r e n g t h f o r s i n g l e c r y s t a l s i n a t o r s i o n a l n o d e c a n b e e x - p r e s s e d a s ( 4 ) : A < 1 0 0 ~ = 6 s / s , A ~ 1 1 0 ~ = 6 s + 6 s ' / . s + ~ ' and A , l l l , = 6 s + 2 6 s ' / s + 2 s I

where s a n d s ' a r e t h e f u n d a m e n t a l s h e a r c o m p l i a n c e s a n d 6 s a n d 6 s ' a r e t h e c o r r e s p o n d i n g a n e l a s t i c r e l a x a t i o n . Y!ith knowing A,,lmn> by Q-l<lmn, m e a s u r e m e n t and u s i n g s , s f m e a s u r e m e n t r e s u l t s , o n e c a n d e t e r m i n e 6 s d i r e c t l y from

< l o o >

r e s u l t a n d 6 s ' by s o l v i n g t h e s i m u l t a n e o u s e q u a - t i o n s . The a p p l i c a t i o n o f t h e a n a l y s i s t o F i g . 2 r e v e a l e d t h a t 6 s i s f i n i t e b u t 6 s ' i s a l m o s t n o n e ( d s 1 / 6 s = 0 + 0 . 2 ) . T h i s c a n be u s e d t o i n f e r t h e c o n f i g u r a t i o n o f N-1i p a i r .

4 . D i s c u s s i o n .

4 - 1 . S t r u c t u r e o f N-H p a i r . - The r e s u l t f o r t h e N-H p a i r t h a t 6sfU 6 s 8 + 0 i s compared w i t h t h e s e l e c t i o n r ~ l e ( ~ ) f o o r p i n t d e f e c t s w i t h v a r i - o u s symmetry t o r e v e a l t h a t t h e a x i s t o c o n n e c t :: a n d K i s d i r e c t e d t o

. T h i s i s a s i m i l a r r e s u l t w i t h t h a t o f t h e 0-t1 p a i r n e a r 9 0 ~ ; ~ ) i l e c e n t c h a n n e l i n g e x p e r i m e n t s ( 6 ) ( 7 ) and t h e o r e t i c a l c a l ~ u l a t i o n ( ~ ) h a v e s u g g e s t e d t h e H o c c u p i e s o c t a h e d r a l s i t e n e a r i n t e r s t i t i a l i m p u r i t i e s . I f t h i s i s a p p l i e d t o t h e p r e s e n t , H i s i n f e r r e d t o o c c u p y t h e t h i r d n e a r e s t o - s i t e o f N - i m p u r i t y . Such a p a i r c o n f i g u r a t i o n h a s a l r e a d y b e e n p r o p o s e d by Zapp and ~ i r n b a u m ( ~ ) a s o n e o f g o s s i b l e c o n f i g u r a t i o n s f o r t h e 0-11 p a i r n e a r 200K.

I f t h e r e l a x a t i o n s t r e n g t h f o r t h e t r i g o n a l d i p o l e , ( 4 ) 6 s = ( 4 c o v o / 9 k ~ ) (A1 -X2j i s a p p l i e d t o t h e

< l o o >

N - H r e s u l t , A l -A2 i s o b t a i n e d a s 3 . 0 3 6 . A l s o i f X1+2A2=0.174 f o r 1.1 i n N b ( l O ) i s assumed f o r N i n t h e p a i r , A 1 and A g a r e o b t a i n e d a s 0 . 1 0 and 0 . 0 7 , r e s p e c t i v e l y .

As f o r t h e 0-H p a i r i n t i l e p r e s e n t , t h e c o n f i g u r a t i o n i s s t i l l i n q u e s t i o n . The 0-M p e a k i s somehow b r o a d e r a n d t h e t e m p e r a t u r e i s h i g h e r t h a n t h o s e o f

< l o o >

a n d < 1 1 0 > i n c o n t r a s t t o N-H. T h i s may b e

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JOURNAL DE PHYSIQUE

due t o t h a t b o t h 6 s and 6 ' s g i v e r i s e t o two c l o s e l y s e p a r a t e d p e a k s i n t h e <111> 0-H s p e c i m e n . So o n e c a n n o t a p p l y t h e method o f t h e a n a l y - s i s ( 3 - 2 ) f o r t h e c a s e o f 0-FI, s i n c e i t i s b a s e d m e r e l y on t h e p e a k h e i g h t .

4 - 2 . The jump r a t e o f H i n t h e 0-H p a i r . - F i g . 4 summarizes t h e H jump r a t e i n a n 0-H p a i r a s m e a s u r e d by Q - ' measurement w i t h s i n g l e c r y s t a l s . F i g . 4 r e v e a l s t h a t t h e p r e s e n t r e s u l t s f a l l on t h e a r r h e n i u s e x t r a p o - l a t i o n o f h i g h t e m p e r a t u r e 6s r e l a x a t i o n . T h i s s u g g e s t s t h a t t h e tem- p e r a t u r e d e p e n d e n c e o f t h e N jump r a t e t o g i v e r i s e t o t h e 6 s r e l a x a - t i o n d o e s n o t d e v i a t e t o o much from t h e a r r e h n i u s r e l a t i o n between SOK a n d 200K. The T' law p r o p o s e d f o r t h e H jump r a t e a t low t e m p e r a t u r e s i s n o t a p p r o p r i a t e n e a r SOK, s i n c e t h e Debye c u r v e W T / ( ~ + ( W T ) ~ ) c a l c u - l a t e d w i t h T - ' = c T' ( c i s f i x e d by t h e r e l a t i o n w r = l a t T ) g i v e s a p e a k o f h a l f w i d t h o f 20X w h i c h i s i n d i s a g r e e m e n t w i t h t h e p r e s e n t P

(10K)

.

A s f o r 6 s ' r e l a x a t i o n , no p e a k h a s b e e n o b s e r v e d on t h e a r r e h n i u s e x t r a p o l a t i o n (75K, 1 H z ) . T h e r e a r e two p o s s i b i l i t i e s t o e x p l a i n i t w i t h i n t h e f r a m e work o f t h e 0-H p a i r model by Zapp and Birnbaum. I f t h e i r f i r s t model ( < l o o > m o n o c l i n i c t o g i v e b o t h 6 s and 6 s ' ) i s assumed, t h e H jump t o g i v e 6 s r e l a x a t i o n d o e s n o t much d e v i a t e from t h e a r - r e h n i u m r e l a t i o n . However t h e jump t o g i v e 6 s ' d e v i a t e s a n d g i v e s r i s e a 6 s ' t y p e p e a k , c l o s e t o 6 s t y p e peak i n o u r s p e c i m e n .

I f their,.'s/econd model ( t h e c o e x i s t e n c e o f < 1 1 0 > m o n o c l i n i c t o g i v e 6 s a n d

< l o o >

o r t h o g o n a l t o g i v e 6 s ' a t 200K) i s a s s u m e d , t h e l a c k o f 6 s ' r e l a x a t i o n i n t h e p r e s e n t may i m p l y s t h a t t h e

< l o o >

o r t h o i s un- s t a b l e a n d o n l y < 1 1 0 > mono i s p r e s e n t a t low t e m p e r a t u r e s .

A t p r e s e n t o u r e x p e r i m e n t s a r e n o t y e t d e t a i l e d enough t o d i s t i n - g u i s h t h e two c a s e s . The r e s u l t f o r 0-H i s n o t d e t a i l e d enough t o r e s o l v e t h e 50K p e a k i n two p e a k s t o s u p p o r t t h e f i r s t model. And y e t t h e 0-H p e a k i s b r o a d e r and s h i f t e d t o h i g h r e r t e m p e r a t u r e by a few d e g r e e which i s i n c o n t r a d i c t i o n w i t h t h e s e c o n d model where o n l y 6 s t y p e p e a k s h o u l d be p r e s e n t f o r a l l o r i e n t a t i o n s a t t h e same t e m p e r - a t u r e f o r t h e same f r e q u e n c y . F u r t h e r ; e x p e r i m e n t s a r e i n p r o g r e s s t o - g e t h e r w i t h i s o t o p e s e x p e r i m e n t s (D and T ) , which w i l l be r e p o r t e d e l s e w h e r e .

5. R e f e r e n c e s

.

( 1 ) H.K. Birnbaum P r o c . I n t . C o n f . "Hydrogen i n M e t a l s " blinakami, J a p a n . p u b l i s h e d by J a p a n I n s t i t u t e o f M e t a l s ( 1 9 8 0 ) .

( 2 ) P . S c h i l l e r Nuovo Cimento, 33B(1976)226.

( 3 ) G.P. P f e i f f e r a n d H . Wipf, J. Phys. F. 6 ( 1 9 7 6 ) 1 6 7 .

( 4 ) B.S. B e r r y and A.S. Nowick i n " P h y s i c a l A c o u s t i c s 1 1 1 P a r t A"

e d i t e d by W.P. Mason, p u b l i s h e d by Academic P r e s s ( 1 9 6 6 ) . ( 5 ) K . J . C a r r o l , J.A.P. 36, (1965)3689.

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( 6 ) H . D . C a r s t a n j e n Rep. I n t . M e e t i n g "Hydrogen i n M e t a l s " MOnster ( 1 9 7 9 ) . ( 7 ) K . Ozawa, S . Yamaguchi, Y . F u j i n o , 0 . Y o s h i n a r i , M. Koiwa a n d M .

f i i r a b a y a s h i , N u c l . I n s t . Ivleth. 1 4 9 ( 1 9 7 8 ) 4 0 5 . ( 3 ) H . S u g i m o t o and Y . F u k a i , R e f . 1.

( 9 ) P . E . Zapp a n d H . K . Birnbaum, A c t a M e t . 2 8 ( 1 9 8 0 ) 1 2 7 5 .

( 1 0 ) H . P e i s l i n "Hydrogen i n M e t a l s I " E d i t e d by G . A l e f e l d a n d J . Y61kl p u b l i s h e d by S p r i n g e r V e r l a g ( 1 9 7 8 ) .

F i g . 1 Q - I r e s u l t s f o r Nb-0-H p o l y - c r y s t a l s . c i n a t . % . F o r a h i g h p u r i t y s p e c i m e n

O<SOat.ppm. f=0.76Hz.

F i g . 3 R e s u l t s f o r s i n g l e c r y s t a l Nb-0-H.

F i g . 4 A r r e h n i u s p l o t f o r B F i g . 2 R e s u l t s f o r Nb-N-H jump i n a 0 - H p a i r A E : l o n g .

o r f l e x u a l . A G : t o r s i o n . s i n g l e c r y s t a l s .