THE α PEAK IN DEFORMED NIOBIUM AND TANTALUM AND THE PROBLEM OF HYDROGEN IMPURITIES

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THE α PEAK IN DEFORMED NIOBIUM AND TANTALUM AND THE PROBLEM OF HYDROGEN

IMPURITIES

G. Funk, M. Maul, H. Schultz

To cite this version:

G. Funk, M. Maul, H. Schultz. THE α PEAK IN DEFORMED NIOBIUM AND TANTALUM AND

THE PROBLEM OF HYDROGEN IMPURITIES. Journal de Physique Colloques, 1983, 44 (C9),

pp.C9-711-C9-716. �10.1051/jphyscol:19839107�. �jpa-00223341�

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Colloque C9, suppl6ment au n012, Tome 44, d6cembre 1983 page C9-711

THE a PEAK I N DEFORMED NIOBIUM AND TANTALUM AND THE PROBLEM OF HYDROGEN IMPURITIES

G. Funk, M. ~aul' and H. Schultz

Max-PZanck-Institut fiir MetaZZforschung, Institut fiir Physik,

Heisenbergstrasse 2 , 0-7000 Stuttgart 80 and Institut fiir Theoretische und Angewandte PPlysik der Universitiit Stuttgart, F.R.G.

' ~ a ~ z e r s AG, FZ-9496 Buzzers Liechtenstein

A b s t r a c t

-

Hydrogen degassing o f Nb and Ta can be achieved e f f e c t i v e l y by Pd-surface l a y e r s and annealing i n a i r o r low pressure oxygen atmosphere a t 420-450K. The H-Snoek-Koester peak can be removed completely and t h e i n t r i n s i c d i s l o c a t i o n r e l a x a t i o n peaks a ( a l ) can be observed. D e t a i l s o f the e x p e r i - mental procedure a r e reported. The i n t r i n s i c a ( % ' ) maximum appears i n h i g h p u r i t y Nb a t 46 K ( 1 kHz), and i n h i g h p u r i t y Ta a t 48 K ( 1 kHz).

Small t r a c e s o f hydrogen i n niobium o r tantalum may suppress t h e i n t r i n s i c d i s l o c a - t i o n r e l a x a t i o n a t low temperatures ( a peak) and c r e a t e a Snoek-Koester peak a t somewhat h i g h e r temperature. A l o n g standing controversy on t h i s p o i n t was solved a t t h e r e c e n t conference ICIFUAS-7 ( 1 ) - ( 4 ) . I n t h e s t u d i e s o f t h e authors on t h i s problem i t was shown t h a t l o n g t i m e u l t r a - h i g h vacuum (UHV) degassing treatments ( - 1 week) a r e r e q u i r e d t o remove hydrogen i m p u r i t i e s from h i g h p u r i t y niobium ( 2 ) ( 5 ) o r tantalum (6) t o l e v e l s below 1 atppm. But even f o l l o w i n g such treatments some small t r a c e s o f hydrogen are present, and u s u a l l y one observes two d i s l o c a t i o n i n t e r n a l f r i c t i o n peaks, a small r e s i d u a l H-Snoek-Koester (S-K(H)) peak and t h e i n t r i n s i c a ( a i ) peak ( a and a ' has n o t been separated up t o now). I n f i g . 1 we show t h e r e s u l t o f such a l o n g time UHV degassing on t h e d i s l o c a t i o n i n t e r n a l f r i c t i o n peaks i n tantalum ( 6 ) , which behaves very s i m i l a r as e a r l i e r r e p o r t e d f o r niobium ( 2 ) ( 5 ) .

F i g . 1

cation i n t e r n a l f r i c t i o n peaks o f h i g h p u r i t y Ta. ( 1 ) UHV degassed 7 days+l% p l a s t i c bending: a ( a 8 ) a t 43 K and S-K(H) peak a t 180 K. ( 2 ) Same specimen a f t e r ( 1 ) doped e l e c t r o - l y t i c a l l y w i t h some'atppm H.

I n t h e f o l l o w i n g we r e p o r t on another technique o f hydrogen degassing, which was r e c e n t l y suggested by Rodrigues and Kirchheim ( 7 ) . A t h i n Pd l a y e r , evaporated on t h e surface o f an UHV annealed Nb o r Ta specimen apparently reduces the surface bar- r i e r f o r t h e f o l l o w i n g r e a c t i o n :

4 H ( i n Nb)

+

O2 = 2 H70(in a i r )

+

^AGO

.

As w i l l be shown below, h e a t i n g o f ~ b o r ~ a - w i t h a Pd surface l a y e r i n low pressure oxygen (200 mbar) removes hydrogen q u a n t i t a t i v e l y from the metal.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19839107

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C9-712 JOURNAL DE PHYSIQUE

Table 1: The p r e p a r a t i o n o f h i g h - p u r i t y hydrogen degassed Nb o r Ta.

1. UHV high-frequency h e a t i n g device

decarburi z a t i o n T( K) ~ ( m b a r ) t (hour)

o f Nb o r Ta 2150 4 x 1 0 - ~ O2 0.5

degassing o f H

f o r Nb o r Ta 1500 l x 1 0 - ~ O 3

degassing o f 0,N Nb Ta

2. UHV-evaporation apparatus

Evaporation o f Pd on a l l surfaces o f t h e specimen (-0.2 um)

3. UHV-measuring c r y o s t a t e 10K-500K

H degassing i n p o s i t i o n f o r measuring o f damping and frequency (bending o s c i l l a t i o n s ) and p l a s t i c deformation i n s i t u .

T=420-450 K, Po2=200 mbar, 1-3 days

Our p r e p a r a t i o n steps a r e i n d i c a t e d i n t a b l e 1. Thin s i n g l e c r y s t a l s p l a t e s 3 0 ~ 3 ~ 0 . 4 mm, were o b t a i n e d by spark e r o s i o n from s i n g l e c r y s t a l rods, prepared by electron-beam zone m e l t i n g i n UHV. Preparation s t e p 1 served f o r d e c a r b u r i z a t i o n , degassing and doping w i t h 0 o r N ( i f r e q u i r e d ) by high-frequency h e a t i n g i n s i d e a UHV system.

A f t e r s t e p 1, t h e specimen was q u i c k l y t r a n s f e r r e d i n t o another UHV-system, contain- i n g an evaporation source f o r Pd evaporation. During t h i s t r a n s f e r t o t h e o t h e r apparatus, t h e specimen i s exposed t o t h e open a i r and t h e f o r m a t i o n o f a t h i n oxygen surface l a y e r must be expected, which i s known t o a c t as b a r r i e r f o r hydrogen. There- f o r e a b e t t e r procedure would be t o evaporate t h e Pd l a y e r i n t h e same apparatus as used f o r s t e p 1. However, by t e c h n i c a l reasons o u r procedure was as described and was working s a t i s f a c t o r i l y . A Pd l a y e r o f -0,2 um thickness was evaporated as p r e p a r a t i o n s t e p 2.

A f t e r s t e p 2, t h e specimen was t r a n s f e r r e d i n t o t h e measuring apparatus, an a l l - m e t a l UHV-system, c o n t a i n i n g a c r y o s t a t e , where t h e specimen c o u l d be operated i n bending o s c i l l a t i o n s (0.3-1 kHz) by e l e c t r o s t a t i c d r i v i n g and d e t e c t i n g between 10 K and 500 K ( 5 ) . I n s i d e t h i s system t h e specimen was heated t o 420-450 K i n an atmosphere o f 200 mbar oxygen gas f o r several hours o r days ( s t e p 3 ) . The specimen c o u l d be p l a s t i c a l l y deformed i n s i t u by bending f o r i n t r o d u c t i o n o f d i s l o c a t i o n s . The complete removal of hydrogen i s i n d i c a t e d by t h e disappearence o f t h e S-K(H) peak.

This r e q u i r e d a degassing t i m e o f 2-3 days.

Fig.2 shows f o r Ta t h e gradual decreasing o f t h e S-K(H) peak near 180 K (1.2 kHz) and the appearance and growth o f t h e i n t r i n s i c d i s l o c a t i o n r e l a x a t i o n peak a(a') a t 48 K.

I should be noted t h a t t h e degassing treatment near 450 K a l l o w s t h e m i g r a t i o n of oxygen i m p u r i t y atoms i n Nb and Ta and creates d i s l o c a t i o n p i n n i n g . This was a l s o i n s p e c t e d and w i l l be discussed l a t e r .

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-cation i n t e r n a l f r i c t i o n peaks o f h i g h p u r i t y Ta.

( 1 ) UHV degassed 5h+Pd s u r f a c e l a y e r ( s t e p 1+2, t a b l e 1 ) . ( 2 ) - ( 4 ) degassed i n 200 mbar O2 a t 450 K. ( 4 ) completely degassed, a ( a l ) a t 48 K.

Fig.3a

m a t i o n in t e r n a l f r i c t i o n peaks o f h i g h p u r i t y Ta:

( 1 ) Completely degassed as f i g . 2 a ( a ' ) a t 48 K.

( 2 ) Applying o f 20 mbar H2 gas a t 293 K f o r a few seconds, f o l l o w i n g ( 1 ) . A t 180 K t h e S-K(H) peak. The specimen has taken-up hydrogen.

1.24- Fig.36

The frequency vs. T o f t h e specimen o f f i g . 3a. The

1.22- r e l a x a t i o n s t r e n g t h has

s h i f t e t from 50 K t o 200 K by

I

^, ^, ^, ^, ^, ^,

^,

hydrogen pick-up.

1.20

0 5 0 100 150 200 250 300

TLKl-

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I n f i g . 3a and 3b we show t h e e f f e c t o f 20 mbar hydroren gas, i n t r o d u c e d t o t h e apparatus f o r a few seconds a t 293 K. The i n t e r n a l f r i c t i o n ( f i g . 3a) and modulus curve (3b) changed from ( 1 ) t o ( 2 ) . As can be seen, t h e r e l a x a t i o n e f f e c t has s h i f t e d from 50 K t o 200 K by t h i s procedure. C l e a r l y , t h e specimen has taken-up hydrogen a t 293 K from t h e hydrogen a mosphere. I n t h e normal vacuum o f t h e apparatus, 10-8 rnbar d u r i n g pumping, o r 10-' mbar a t pumps o f f , no hydrogen pick-up was observed a t 300 K from t h e r e s i d u a l vacuum pressure gas, as w i l l be shown l a t e r .

Fig.4

m c a t i o n i n t e r n a l f r i c t i o n i n h i g h - p u r i t y Nb. Complete hydrogen degassing by Pd- s u r f a c e l a y e r technique l e t disappear t h e S-K(H) peak, i t remains t h e a ( a l ) peak a t 44 K (0.3 kHz).

The same treatment, as described f o r Ta, was a p p l i e d t o Nb. F i g . 4 shows t h e complete degassed s t a t e o f a h i g h p u r i t y Nb specimen, p l a s t i c a l l y deformed (1% bending). A t 44 K (0.3 kHz) appears t h e a(a') peak. I n Nb we inspected t h e i n f l u e n c e o f oxygen m i g r a t i o n d u r i n g h e a t i n g t o 500 K on the p i n n i n g o f d i s l o c a t i o n s . F i g . 5-8 shows a sequence o f measurements r e l a t e d t o i s o c h r o n a l annealing treatments i n t h e range 300K-500K.

The specimen was a h i g h - p u r i t y Nb s i n g l e c r y s t a l , doped w i t h 25 atppm n i t r o g e n i n o r d e r t o achieve some k i n d of standard f r e e l o o p l e n g t h o f f r e e d i s l o c a t i o n s . The r e s i d u a l oxygen i m p u r i t y c o n t e n t i s expected as -1 atppm.

Fig.5

-cation i n t e r n a l f r i c t i o n i n h i g h p u r i t y Nb (+25 atppm N) f o l l o w i n g complete H degassing by Pd-surface l a y e r technique.

S t a t e b e f o r e isochronal annealing 300-500 K.

6 5-

Niob 7016 C,= 25atppm

f = 650 H Z

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Fig.6

E Z E c a t i o n i n t e r n a l f r i c t i o n

0 f = 6 5 0 Hz

T,=300 K

1

-.o

2-

1 -

Lo-

O7

6 Niob 7016

1

o f h i g h p u r i t y Nb (+25 a t p m N).

Isochronal annealing o f Q-

f

(300 K) background damping.

Same specimen as f i g . 5 . The step a t 420-460 K i n d i c a t e s d i s l o c a t i o n p i n n i n g by mobile oxygen atoms (-1 atppm oxygen b u l k c o n c e n t r a t i o n )

Fig.8

Same specimen as f i g . 7 f o l l o w e d

kt

. . by a H-degassing by Pd-surface

l a y e r technique; a ( a l ) a t . 4 0 K

. .

. . ... ... appears ag i n . Background

. . . ... ...

: '..

_

damping Q-

1

(300K) same as i n

0 f i g . 7 .

50 100 150 200 250 300

T [ K l

-

300 350 400 450 500

T [Kl

-

Fig.7

m c a t i o n i n t e r n a l f r i c t i o n o f h i g h p u r i t y Nb (+25 atppm N).

A f t e r annealing t o 500 K ( f i g . 6 ) t h e S-K(H) peak appears again a t 160 K, t h e a ( a r ) peak (45 K f i g . 5 ) has disappeared.

6 5- 4-

1

₀^{3 -}

-

2- 1-

0 50 100 150 200 250 300

T [Kl- Niob 7016 CN= 25atppm

. . f = 650 Hz . .

.

^. ^T,⁼^{300 K}

. .

-... ^{^}...

"" ,.J.

... ."..

I

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Fig.5 shows t h e a ( a l ) peak near 45 K as observed a f t e r H-degassing (450 K) f o l l o w e d by p l a s t i c bending (-1%) a t 293 K. The specim n was i s o c h r o n a l annealed from 300.K t o 500 K i n t h e vacuum o f t h e apparatus (10- mbar) and t h e background damping a t

5

30 K was measured f o l l o w i n g each annealing step. ( F i g . 6 ) . The s t e p l i k e decrease o f

P

Q-

(300 K) between 420 and 460 K i n d i c a t e s p i n n i n g by mobile oxygen atoms. The meas- urement o f t h e damping a t lower temperatures ( f i g . 7 ) i n d i c a t e s t h a t f o l lo w i n g 500 K annealing mbar) t h e specimen shows t h e S-K(H) peak a t 160 K, t h a t meansthe specimen has picked-up hydrogen from t h e r e s i d u a l vacuum gas a t 500 K. Another degassing treatment (420 K,200 mbar oxygen, 65 hours) removed t h e S-K(H) peak again and we observed t h e a ( a l ) peak near 40 K (0.6 kHz), somewhat reduced i n s i z e compared t o f i g . 5 , however, t h e background damping a t 300 K i n f i g . 8 i s the same as i n f i g . 7 . Therefore, we conclude t h a t t h e a d d i t i o n a l degassing between f i g . 7 and f i g . 8 has n o t i n t r o d u c e d f u r t h e r p i n n i n g .

The p i n n i n g a f t e r annealing t o 500 K i s n o t complete. We observe a r e d u c t i o n o f Q-I (300 K) by 75%. This i n d i c a t e d t h a t e i t h e r n o t enough oxygen atoms f o r complete

p i n n i n g a r e present, o r t h e b i n d i n g energy d i slocation-oxygen i s r e l a t i v e l y low, so t h a t a t 500 K o n l y a d i l u t e atmosphere o f oxygen around t h e d i s l o c a t i o n i s formed.

One can estimate t h a t f o r a b i n d i n g energy o f 0.5 eV and b u l k c o n c e n t r a t i o n o f 1 atppn oxygen we o b t a i n a t 500 K a d i l t e atmosphere o oxyqen atoms, where 3.5% o f t h e d i s -

!?I'

5 ^-

l o c a t i o n s i t e s a r e occupied (10 d i s l o c a t i o n / c m assumed), see ( 8 ) . This s i t u a t i o n appears r e a l i z e d i n our specimen Nb 70/6, f i g . 5-8.

F i n a l l y , we compare t h e p o s i t i o n o f t h e i n t r i n s i c a ( a l ) peak i n niobium and tantalum, as observed here, w i t h e a r l i e r observations. I n our p u b l i c a t i o n Maul e t a l . ( 2 ) we r e p o r t e d t h e i n t r i n s i c a ( a l ) peak i n niobium a t 30 K (1.5 kHz) f o r a c r y s t a l doped w i t h 800-1000 atppm oxygen. This appeared t o agree approximately w i t h t h e e a r l i e r

r e p o r t e d 8 peak o f Mazzolai e t a l . ( 3 ) a t 27 K (40 kHz) i n "impure" m a t e r i a l . I n c o n t r a s t w i t h t h i s r e s u l t we r e p o r t e d i n ( 2 ) f o r h i g h p u r i t y Nb a peak temperature o f 70 K (1.5 kHz) and considered t h i s d i f f e r e n c e 30 K t o /O K as due t o t h e i n f l u e n c e o f t h e f r e e l o o p l e n g t h o f d i s l o c a t i o n s . T h i s was questioned by Fantozzi and R i t c h i e

( 1 ) . Here, i n o u r present paper, we observed f o r h i g h p u r i t y Nb 46 K (1 kHz) as peak temperature. This i s compatible w i t h t h e r e s u l t o f Mazzolai e t a l . ( 3 ) r e g a r d i n g t h e frequency d i f f e r e n c e . I n s p e c t i n g again o u r e a r l i e r r e s u l t s on t h e 70 K ( 1 . 5 kHz) peak, we n o t i c e t h a t t h i s peak p o s i t i o n r e s u l t e d from a s p e c i f i c specimen h i s t o r y : P l a s t i c

deformation a t 20 K f o l l o w e d by annealing steps a t 40 K, 80 K, 100 K

...

(see ( 5 ) , f i g . 17,18). The peak showed a development and s h i f t e d from 45 K t o 70 K d u r i n g t h i s treatment. We assume t h a t t h e 70 K peak i s an anlogue t o t h e H a s i g u t i peaks i n f .c.c.

metals, and r e f l e c t s a s p e c i f i c d i s l o c a t i o n p o i n t d e f e c t i n t e r a c t i o n . I n Tawe observe t h e i n t r i n s i c a ( a l ) peak a t 48 K ( 1 kHz). This agrees reasonable w i t h M a z z o l a i ' s ( 3 ) 8 peak a t 27 K (20 kHz). I t f p l l o w s t h a t t h e e a r l y suggestions o f Mazzolai and Nuovo ( 3 ) , concerning t h e i n t r i n s i c d i s l o c a t i o n i n t e r n a l f r i c t i o n peaks i n Nb and Ta, ob- t a i n f u l l support by t h e new degassing technique, and t h a t t h e f o r m e r l y named a r e - l a x a t i o n ( 9 ) - ( 1 4 ) i s indeed a S-K(H) r e l a x a t i o n , as suggested a l s o by Ferron, Q u i n t a r d andde Fouquet (4), and Shibata e t a l . (15).

References

( 1 ) G. Fantozzi and I . G . R i t c h i e , J. de Physique C5

-

3 (1981) ( 2 ) M. Maul and H. Schultz, J. de Physique C5

-

73 (1981) ( 3 ) F.M. Mazzolai and M. Nuovo, S o l i d S t a t e Comm. 7, 103 (1969)

( 4 ) G. Ferron, M. Q u i n t a r d , and J. de Fouquet, I n t z r n a l F r i c t i o n and U l t r a s o n i c A t t e n u a t i o n i n Solids, p.55, Pergamon Press, Oxford 1980, Ed. C.C. Smith ( 5 ) M. Maul, D i s s e r t a t i o n U n i v e r s i t a t S t u t t g a r t , 1981

( 6 ) G. Funk, Diplomarbeit U n i v e r s i t a t S t u t t g a r t 1981

( 7 ) J.A. Rodrigues and R. Kirchheim, S c r i p t a Met., 17, 159 (1983) (8)

U.

Rodrian and H. Schultz, Z. Metallkde. 73, 2171982)

(93 R.H,. Chambers, Physical Acoustics, Vol.3A, p. 123, Academic Press, New York(1966) (10) G. Knoblauch, Acta Met. 24, 491 (1976)

(11) R. Klam, H.-E. Schaefer,Tnd H.Schul t z , I n t e r n a l F r i c t i o n and U . A t t . i n S o l i d s , p.671,Univers. o f Tokyo Press,Tokyo 1977,Eds. R. H a s i g u t i and N. Mikoshiba (12) R. Klam, H. Schultz, and H.-E. Schaefer, Acta Met. 27,205 (1979), - 28,259 (1980) (13) H.-E. Schaefer, H. Schultz, and H.-P. Stark, r e f .

(q,

p. 25

(14) H. Schultz, U. Rodrian, and M. Maul, r e f . (4) p . 19

(15) K. Shibata, M.Koiwa, O.Yoshinari, Trans.Jap.Inst.Met.

2,

491 (1978)