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STUDIES OF HYDROGEN TRAPPED BY
NITROGEN OR OXYGEN IN NIOBIUM WITH
ULTRASONIC ATTENUATION TECHNIQUE AND
RESISTIVITY MEASUREMENTS
San-Qiang Shi, W. Li
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C10, suppl6ment au n012, Tome 46, d6cembre 1985 page C10-91
STUDIES OF HYDROGEN TRAPPED BY NITROGEN OR OXYGEN IN NIOBIUM WITH ULTRASONIC ATTENUATION TECHNIQUE AND RESISTIVITY MEASUREMENTS
SAN-QIANG SHI AND
W.B.
LIDept.
of Physics,
B e i j i n gUniversity of Iron
and S t e e lTechnology, Bei j i n g , C h i n a
A b s t r a c t
-
U l t r a s o n i c a t t e n u a t i o n experiment showed t h a t H occupies t h e t h i r d--
n e a r e s t o - s i t e of N i n niobium, t h e a c t ' a t i o enthalpy o f N-H p a i r was 0.20 eV, and t h e frequency f a c t o r was 3.0x10'qsec-P. R e s u l t s of r e s i s t i v i t y measurements showed t h a t t h r e e H atoms can be t r a p p e d p e r oxygen i n t e r s t i t i a l a t l o w t e m p e r a t u r e i n niobium, t h e t r a p p i n g e n t h a l p y b e i n g 0.13 eV.
I
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INTRODUCTIONSo f a r t h e r e a r e many i n v e s t i g a t i o n s on Nb-0-H o r Nb-N-H systems, and i t has been shown t h a t N and 0 can s t r o n g l y t r a p H by f o r m i n g N-H and 0-H p a i r s / I / . However, t h e s t r u c t u r e s of N-H and 0-H p a i r s s t i l l a r e n o t c l e a r l y known and t h e r e a r e d i f f e r i n g o p i n i o n s on t h e number o f H atoms t r a p p e d by one oxygen.
The purposes o f o u r experiments a r e ( 1 ) t o s t u d y t h e s t r u c t u r e o f t h e N-H p a i r and ( 2 ) t o o b t a i n t h e a c t i v a t i o n e n t h a l p y o f N-H r e l a x a t i o n and t h e frequency f a c t o r a t t h e temperature range a t which A r r h e n i u s r e l a x a t i o n i s a v a i l a b l e , and ( 3 ) t o examine t h e number of H atoms t h a t one oxygen may t r a p i n niobium.
I 1
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EXPERIMENTAL PROCEDURE2.1. Nb-N-H U l t r a s o n i c A t t e n u a t i o n Experiments
The s i n g l e cr,ystal samples were made f o r u l t r a s o n i c a t t e n u a t i o n experiments. They had a p u r i t y o f 99.99% and were c u t i n t o c y l i n d e r s o f $ 2 0 ~ 1 0 mm a l o n g t h e d e s i r e d o r i e n t a t i o n s . The o p p o s i t e faces were made f l a t and p a r a l l e l by hand p o l i s h i n g . The n i t r o g e n c o n c e n t r a t i o n was o b t a i n e d by a n n e a l i n g i n a q u a r t z chamber a t 1273 K a t a n i t r o g e n p r e s s u r e l a r g e r t h a n 1 atm f o r about 30 hours. The hydrogen l o a d i n g was performed e l e c t r o l y t i c a l l y a t 350 K. $he e l e c t r o l y t e c o n s i s t e d of 0.05% H2S04. The c u r r e n t d e n s i t y was about 15 mA p e r cm sample s u r f a c e and t h e l o a d i n g t i m e was about 5 hours. Chemical a n a l y s i s o f samples was c a r r i e d o u t u s i n g vacuum f u s i o n f o r 0,N and vacuum e x t r a c t i o n f o r H w i t h t h e r e s u l t s of O( .12at%), N(O.llat%) and H(0.24at%).
It was unexpected t h a t t h e oxygen c o n c e n t r a t i o n was So h i g h . The reason was t h a t we do n o t have an UHV system.
C10-92 JOURNAL
DE
PHYSIQUEA t t e n u a t i o n was measured by u s i n g a pulse echo technique a t frequencies o f 45, 75 and 105 MHz. L o n g i t u d i n a l modes were used f o r a l l measurements and pulses were propagated along (110) and (100) d i r e c t i o n s r e s p e c t i v e l y .
2.2. Nh-0-H R e s i s t i v i t y Experiments
The p o l y c r y s t a l samples were made f o r r e s i s t i v i t y measurements. They were 60 pm t h i c k and 1
mm
wide w i t h a p u r i t y o f 99.9%. The main s u b s t i t u t i o n a l elements were Fe(0.005%), Si(0.005%), and Mo(O.Ol%). The oxygen c o n c e n t r a t i o n was obtained i n a chamber f i l l e d by argon ( c o n t a i n i n g oxygen) a t 1120 K f o r 30 min, t h e n t h e samples cooled down t o room temperature i n a few seconds t o prevent t h e formation of oxygen c l u s t e r s . The hydrogen 1 oading was performed e l e c t r o l y t i c a l l y a t 300 K.The r e s u l t s o f chemical a n a l y s i s a r e shown i n t a b l e 1.
I 1 1
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RESULTS AND DISCUSSION3.1. U l t r a s o n i c A t t e n u a t i o n Experiments
Table 1. Chemical a n a l y s i s o f Ni -0-H p o l y c r y s t a l
SAMPLE O(at%) H(at%)
3.1.1. (110) samples: 1 1 .O 1.97
2 1.0 2.66
The h i g h temperature peaks ( f i g . 1: 3 1 .0 4.15
45 MHz-250K. 75 MHz-265K. f i a . 3:
.
105 MHz-275 ) are N-H
If
peaks(4-'
=0.3-1.5~10- ). We have t h r e e reason!: (1). These peaks a r e n o t H - d i s l o c a t i o n r e l a x a t i o n . a) H - d i s l o c a t i o n y f l a x a t ' o n ' s a c t i v a t i o n enthalpy was 0.30 eV /2/ and frequency f a c t o r was 9.7 x 10 31. But f o r our h i g h temperature peak case these were 0.20 eV and 3.0 x 101fetec-i r e s p e c t i v e l y . b) M. Maul andlH. S c h u l t z have found: O(N) reduce t h e peak temperature (Tm) and t h e peak h e i g h t
(Q-
) /4/. Fig. 2 shows t h a t t h e d i s l o c a t i o n r e l a x a t i o n , if i t e x i s t s , should be lowermthan 245 K.(2). These peaks a r e n o t 0-H p a i r r e l a x a t i o n because P.E. Zapp has found t h a t 0-H peak appeared i n 190-230 K (frequency: 30-130 MHz)
111.
( 3 ) . Comparing f i g . 2 w i t h fig. 3, we can see t h a t t h e h i g h temperature peak occurred o n l y under t h e c o n d i t i o n t h a t H and N e x i s t e d simultaneously.The low temperature peak may be a p o l y - r e l a x a t i o n process. i.e., 0-H r e l a x a t i o n , H- d i s l o c a t i o n r e l a x a t i o n , o r even more compl i cated poly-component re1 axation.
Fig. 2 shows a r e l a x a t i o n a t about 245 K. A f t e r annealing f o r n i t r o g e n doping, t h i s peak disappeared ( f i g . 3). So we supposed t h a t t h i s peak was H - d i s l o c a t i o n
r e l a x a t i o n .
I n f i g . 4, Tm were shown t o obey an Arrhenius r e l a t i o n very w e l l . We obtained an a c t i v a 'on en halpy o f N-H p a i r r e l a x a t i o n of 0.20 eV, and a frequency f a c t o r o f 3 . o x l o I l sec-1.
3.1.2. Comparing (100) samples w i t h (110) samples:
Fig. 5 and f i g . 6 show t h e r e s u l t s o f (100) sample measurements. 45 MHz nearby 250 K and 75 MHz nearby 265 K do n o t have c l e a r peak, but have peaks i n lower
temperatures. Torsion pendulum measurements t o l d us t h a t t h e temperatures o f N-H peak (T,) was independent o f t h e c r y s t a l o r i e n t a t i o n 151. Concluding from t h e above r e s u l t s , we can say: 6J -0, 6J # 0 f o r N-H r e l a x a t i o n . I n our case, 6JlO0 = 6S1/3, 6J
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6S/3. ~ h h O P e s u l t s P = o , 6 9 0 are compared w i t h t h e s e l e c t i o n r u l e /6/ f o r p 8 % d e f e c t s w i t h v a r i o u s symmetry t o reveal t h a t t h e a x i s t o connect N and H i s d i r e c t e d t o ( I l l ) , i.e., H occupies t h e t h i r d nearest octahedral s i t e t o N- i m p u r i t y . This r e s u l t i s i n agreement w i t h t h e observation by R. Hanada e t a1 151 (- 1 Hz).background o f f i g . 6 i s h i g h e r t h a n t h a t o f f i g . 5. T h i s phenomenon i s some evidence f o r i n c r e a s i n g d i s l o c a t i o n d e n s i t y .
3.2. R e s i s t i v i t y Measurements
The method and t h e p r i n c i p l e o f o u r work a r e t h e same a< t h a t o f
G.
P f e i f f e r and H. W i pf /7/.I n f i g s . 7-10, t h e b l a c k p o i n t s a r e r e s i s t i v i t y measurement r e s u l t s , t h e f u l l curves a r e t h e o r e t i c a l curves, t h e broken l i n e i n d i c a t e s t h e r e s i s t i v i t y values o f oxygen- f r e e niobium, q stands f o r t h e number o f H atoms t r a p p e d by each oxygen
i n t e r s t i t i a l , and E i s t h e t r a p p i n g e n t h a l p y . The i n c r e a s e of t h e r e s i s t i v i t y p e r u n i t c o n c e n t r a t i o n of t r a p p e d H was 0.40 uacm.
Fig. 7 shows q > 2, and f i g . 8 shows q > 3. F i n a l l y f i g . 9 shows q = 3.
Consirlering t h e c o n c e n t r a t i o n o f H, we l e a r n t h a t one oxygen atom m i g h t a t most t r a p t h r e e H atoms a t l o w temperature. T h i s r e s u l t i s i n agreement w i t h t h e i n t e r n a l f r i c t i o n work (KHz) o f P. S c h i l l e r and A. Schneiders /8/, i n w h i c h t h e y found t h a t t h e i n t e r n a l f r i c t i o n reached a maximum v a l u e when t h e c o n c e n t r a t i o n of 0 was 0.06at% and H 0.2at%. It s h o u l d be n o t i c e d t h a t q < 3 a t h i g h temperature, i.e., a p a r t o f t h e H atoms were on o r d i n a r y ( f r e e ) i n t e r s t i t i a l s i t s , n o t on t r a p p i n g s i t e s .
Fig. 10 shows t h e t r a p p i n g e n t h a l p y was about 0.13-0.14 eV. R e s u l t s f o r o t h e r samples were t h e same. T h i s v a l u e i s a l i t t l e more t h a n t h e p r e c i p i t a t i o n e n t h a l p y o f H i n niobium (0.12 eV / 7 / ) , and a l i t t l e more t h a n t h a t o f N-H p a i r (0.12 eV / 7 / ) . T h i s r e s u l t i n d i c a t e s t h a t f o r m i n g an 0-H p a i r i s e n e r g e t i c a l l y more f a v o r a b l e t h a n p r e c i p i t a t i o n o r f o r m i n g an N-H p a i r .
REFERENCES
/1/ P.E.Zapp, Illinois University,~OE/ER/01198-1299; 139 (1979). 72/ R.Klam and others, Acta.Metall.27, 2 0 5 (1979).
/3/ R.H.Chambers and H.Schultz, Acta.Metall.10, 466 (1962). /4/ M.Maul and H.Schultz, ICIFUAS-7, 73 (1981).
/5/ R.Hanada and others, ICIFUAS-7, 757 (1981).
/6/ A.S.Nowick and B.S.Berry, Anelastic Relaxation in Crystalline Solids, Academic Press, New York (1972).
/7/ G.Pfeiffer and H.Wipf, J.Phys,F: Metal Phys.6, 1 6 7 (1976). /8/ P.Schiller and A.Schneiders, Phys.Stat.Sol.(a)29, 375(1975).
Fig.1 Internal friction&ultra- sonic attenuation vs. tempera- t u r e in t h e (110) direction.
Fig.2 Internal friction a n d ul- trasonic attenuation vs. tempe-
