SUPERCONDUCTIVITY OF DUCTILE TITANIUM-NIOBIUM-BASED AMORPHOUS ALLOYS

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SUPERCONDUCTIVITY OF DUCTILE TITANIUM-NIOBIUM-BASED AMORPHOUS

ALLOYS

A. Inoue, T. Masumoto, C. Suryanarayana, A. Hoshi

To cite this version:

A. Inoue, T. Masumoto, C. Suryanarayana, A. Hoshi. SUPERCONDUCTIVITY OF DUCTILE

TITANIUM-NIOBIUM-BASED AMORPHOUS ALLOYS. Journal de Physique Colloques, 1980, 41

(C8), pp.C8-758-C8-761. �10.1051/jphyscol:19808189�. �jpa-00220292�

JOURNAL DE PHYSIQUE

CoZZoque C8, suppldment au n08, Tome 41, aoGt 1980, page C8-758

SUPERCONDUCTIVITY OF DUCTILE TITANIUM-NIOBIUM-BASED AMORPHOUS ALLOYS

A. Inoue, T. Masumoto, C. Suryanarayana

*

and A . Hoshi

The Research I n s t i t u t e for Iron, SteeZ and Other Metals, Tohoku University, Sendai 980, Japan.

* ~ e ~ a r t m e n t o f MetaZZurgicaZ Engineering, B m a s Hindu U n i v e r s i t y , Varanasi-221005, India.

INTRODUCTION

Superconducting m a t e r i a l s p o s s e s s i n g good me- c h a n i c a l p r o p e r t i e s a s w e l l a s a h i g h t r a n s i t i o n temperature(Tc) a r e d e s i r a b l e f o r a p p l i c a t i o n s . S i n c e amorphous a l l o y s e x h i b i t s u p e r c o n d u c t i v i t y

/1/

and h i g h s t r e n g t h a s w e l l a s good d u c t i l i t y compared t o t h e c r y s t a l l i n e a l l o y s / 2 / , i t

i s

expected t h a t a s u p e r c o n d u c t i n g m a t e r i a l p o s s e s s i n g a h i g h Tc a s w e l l a s good mechanical p r o p e r t i e s may b e o b t a i n e d i n t h e amorphous s t a t e . F u r t h e r , i t was r e c e n t l y shown / 3 / t h a t amorphous s u p e r c o n d u c t o r s a l s o pos- s e s s a h i g h t o l e r a n c e t o i r r a d i a t i o n i n c o n t r a s t t o t h e i r c r y s t a l l i n e c o u n t e r p a r t s . From t h e s e p o i n t s of view, we have i n v e s t i g a t e d t h e c o m p o s i t i o n r a n g e s f o r t h e f o r m a t i o n of amorphous p h a s e s and t h e i r s u p e r c o n d u c t i n g p r o p e r t i e s i n splat-quenched r e f r a c - t o r y metal-based a l l o y s /4-13/ and repor;ed t h a t Ti-, Nb-, Mo- and W-based amorphous a l l o y s e x h i b i t s u p e r c o n d u c t i v i t y above t h e l i q u i d helium tempera- t u r e ( 4 . 2 K ) . More r e c e n t l y , w i t h a view t o g e t su- p e r i o r s u p e r c o n d u c t i n g p r o p e r t i e s i n t h e s e m e t a s t a - b l e a l l o y s , we have c a r r i e d o u t s y s t e m a t i c e x p e r i - ments on t h e e f f e c t of a d d i t i o n a l e l e m e n t s on Ti-Nb- based amorphous a l l o y s . This p a p e r d e a l s w i t h a s - p e c t s i n v o l v i n g t h e composition r a n g e f o r t h e forma- t i o n of t h e amorphous s i n g l e p h a s e i n t h e Ti-IJb-Si-M (M=Mo, Ru, Rh, Pd, Ir, B , C and Ge) systems and t h e mechanical and s u p e r c o n d u c t i n g p r o p e r t i e s of t h e amorphous a l l o y s . These a l l o y i n g e l e m e n t s were chosen t o i n c r e a s e t h e a v e r a g e o u t e r e l e c t r o n con- c e n t r a t i o n ( e / a ) of t h e m e t a l component, s i n c e Tc i n t h e amorphous s t a t e was found t o b e c l o s e l y r e l a t e d t o t h e e / a showing a broad maximum around e / a = 6 . 5 f o r t h e 4d and 5d t r a n s i t i o n - m e t a l s e r i e s / 1 4 / .

EXPERIMENTAL

The a l l o y s were p r e p a r e d from p u r e components under

a

p r o t e c t i v e argon atmosphere i n a n

a r c

f u r - nace. The i n g o t s were r e p e a t e d l y t u r n e d o v e r and r e m e l t e d t o i n s u r e homogeneity of composition. Con- t i n u o u s r i b b o n specimens of a b o u t 1-2 mm w i d t h and

0.02-0.04 mm t h i c k n e s s were p r e p a r e d from t h e s e par- e n t a l l o y s under a p r o t e c t i v e a r g o n atmosphere u s i n g a modified s i n g l e r o l l e r quenching a p p a r a t u s a d a p t e d t o

a

l e v i t a t i o n f u r n a c e d e s c r i b e d i n Ref. / 5 / . Typ- i c a l l y , t h e amount of a l l o y m e l t e d i n one r u n was a b o u t 3 g and t h e r o t a t i o n speed of t h e copper r o l l - e r ( 2 0 cm i n d i a m e t e r ) was a b o u t 4000 rpm. I d e n t i f i - c a t i o n of t h e as-quenched p h a s e s was made by conven- t i o n a l X-ray d i f f r a c t i o n and t r a n s m i s s i o n e l e c t r o n microscopy t e c h n i q u e s .

The s u p e r c o n d u c t i n g t r a n s i t i o n was monitored by measuring t h e r e s i s t i v i t y u s i n g a c o n v e n t i o n a l f o u r - p r o b e method. The specimen c u r r e n t used was 1 m A . The t e m p e r a t u r e was measured w i t h a n a c c u r a c y of

f

0.05

K

u s i n g a c a l i b r a t e d Au-Fe

+

Chrome1 thermo- c o u p l e . The c r i t i c a l c u r r e n t was d e f i n e d a s t h e c u r r e n t a t which a measurable v o l t a g e ( 1 uV) appeared a c r o s s a 50 mm-length specimen i n a l i q u i d helium b a t h a t z e r o f i e l d . Upper and lower c r i t i c a l mag- n e t i c f i e l d ( H c 2 and Hcl) measurements were performed u s i n g a s u p e r c o n d u c t i n g s o l e n o i d f o r magnetic f i e l d s up t o about

7.2

x 106

A/m

a p p l i e d t r a n s v e r s e l y t o t h e specimen i n a l i q u i d helium b a t h .

RESULTS AND DISCUSSION

1. Formation r a n g e and mechanical p r o p e r t i e s of t h e amorphous a l l o y s

F i g u r e s 1 and 2 show t h e f o r m a t i o n r a n g e of amorphous s i n g l e p h a s e f o r t h e Ti-Nb-Si t e r n a r y and Ti55-xNb30MxSi15(M=Mo, Ru, Rh, Pd and I r ) and Ti55 N ~ ~ O S ~ ~ ~ - ~ % ( M = B , C and Ge) q u a t e r n a r y systems. The amorphous p h a s e forms i n t h e wide r a n g e of 0-43 a t . % Nb and 13-21 a t . % S i for,Ti-Nb-Si system and i n t h e r a n g e s of 0-7 at.%Mo, 0-25 at.%Ru, Rh o r Pd and 0-11 a t . % I r f o r Ti55-xNb30MxSi15 systems. A d d i t i o n a l l y , t h e amorphous s i n g l e p h a s e of t h e Ti55Nb30Si15 a l l o y was r e t a i n e d even by t h e replacement of S i w i t h B o r C up t o

7

a t . % and Ge up t o 4 a t . % .

V i c k e r s h a r d n e s s and t e n s i l e f r a c t u r e s t r e n g t h of t h e Ti-Nb-Si and Ti-Nb-Si-B amorphous a l l o y s a r e

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19808189

0

Am.. OAm.+Cry.. .Cry.

V V v

Ti 0

10 20 30 40 50 60, 70 Silicon (at?l0)

F i g . 1 Composition range f o r t h e formation of amor- phous s i n g l e phase i n t h e Ti-Nb-Si system and t h e change i n t r a n s i t i o n temperature(Tc) (marked by numbers on t h e open c i r c l e s ) of t h e amorphous a l l o y s .

F i g . 2 Composition r a n g e f o r t h e formation of arnor- phous s i n g l e phase i n t h e Ti55-,Nb3&Sil5 (M=Mo, Ru, Rh, Pd and I r ) and Ti55Nb30Sil5-, M,(M=B, C and Ge) systems.

about 570 DPN and 2040 MPa. C r y s t a l l i z a t i o n temper- a t u r e s a r e i n t h e range of 690-770

K.

F u r t h e r , a l l t h e amorphous a l l o y s a r e s o d u c t i l e t h a t no c r a c k

i s

found a t t h e t i p of a specimen b e n t through 180'.

These a l l o y s continued t o b e d u c t i l e a t l e a s t f o r

1

h a t temperatures below

670

K.

2. Superconducting p r o p e r t i e s 2-1. T r a n s i t i o n temperature(T,)

A s

shown i n Fig.

1,

t h e Ti-Nb-Si a l l o y s con- t a i n i n g more t h a n about 10 a t . % % show a supercon- d u c t i n g t r a n s i t i o n above l i q u i d helium temperature

(4.2 K). The Tc i n c r e a s e s w i t h i n c r e a s i n g Nb con- t e n t o r d e c r e a s i n g S i c o n t e n t and r e a c h e s 5 . 1 K f o r t h e Ti45Nb40Si15 a l l o y . F i g u r e 3 shows t h e change i n T i of Ti55-xNb3@xSi15 and Ti55Nb30Si15-xMx amorphous a l l o y s w i t h t h e c o n c e n t r a t i o n of a d d i t i o n - a l elements. A s s e e n i n ( a ) , t h e replacement of T i by Mo r e s u l t s i n a d r a s t i c d e c r e a s e of Tc d e s p i t e

2 - 5.

^{% a ) '} Ti55-xNb3~M~xSi15

' 4.0-

c 0

.-

c.

.$ ^3.5-

e

^k

I- \

3.0 0 2 4 6 8 1 0

Molybdenum concentration

(atolo)

l- (M= B,C,Ge)

3.0

0 1 2 3 4 5

Concentrationof additional elements,M(atPlo) F i g . 3 ( a ) change i n t r a n s i t i o n temperature(Tc) of

Ti55-xNb30Mo~Si15 amorphous a l l o y s by t h e replacement of T i w i t h Mo

.

(b) change i n t r a n s i t i o n temperature(Tc) of Ti55Nb3oSipj-, Mx(M=B,

C

and Ge) amorphous a l l o y s by t h e replacement of S i w i t h M elements.

t h a t t h e e / a of m e t a l components i n t h e s e amorphous a l l o y s approaches t h e e / a corresponding t o t h e ex- pected maximum Tc. Superconducting t r a n s i t i o n could n o t b e d e t e c t e d above 3.5 K when T i

i s

r e p l a c e d by Ru, Rh, Pd o r

Ir.

This r e s u l t i n d i c a t e s t h a t a plu- r a l i t y of a l l o y component i s n o t a n e f f e c t i v e method f o r producing amorphous superconductors w i t h a h i g h

Tc.

On t h e o t h e r hand, a s s e e n i n ( b ) , replacement of S i by B b r i n g s about a s l i g h t i n c r e a s e of Tc and t h e maximum v a l u e

i s

5 . 1

K

f o r Ti55Nb30SiloB5 a l l o y . F u r t h e r , one can n o t i c e t h a t replacement of S i w i t h C o r Ge d e c r e a s e s Tc much less t h a n i n t h e c a s e of t h e replacement of T i by a l l o y i n g elements. The above r e s u l t s i n d i c a t e t h a t an e f f e c t i v e element f o r i n c r e a s i n g Tc of Ti-Nb-Si amorphous a l l o y s

i s

only boron. Hence, o u r subsequent r e s e a r c h was focused on t h e Ti-Nb-Si-B q u a t e r n a r y a l l o y s .

The f o r m a t i o n r a n g e of amorphous s i n g l e phase and t h e Tc v a l u e s f o r (Ti-Nb-Si)97B3 a l l o y s a r e shown i n F i g . 4, wherein t h e d a t a of Vickers hard- n e s s a r e a l s o p r e s e n t e d . S i m i l a r t o t h e (Ti-Nb)85 Si15 a l l o y s , t h e (Ti-Nb)85Sil2B3 amorpfious a l l o y s show a superconducting t r a n s i t i o n above 4.2

K

i n a

JOURNAL D IE PHYSIQUE

/

" ^v V V v V v

\o

Ti+3°1~B10 20 30 40 50 60 70 80 Niobium (at.O/o)

Fig. 4 Composition r a n g e f o r t h e f o r m a t i o n of amor- phous s i n g l e phase i n t h e Ti-Nb-Si-B system and t h e changes i n t r a n s i t i o n t e m p e r a t u r e

(T,) and V i c k e r s hardness(Hv) of t h e amor- phous a l l o y s .

l i m i t e d composition r a n g e . The Tc v a l u e i n c r e a s e s w i t h i n c r e a s i n g Nb c o n t e n t , a t t a i n s 5.4 K f o r Ti45 Nb40Sil2B3 and d e c r e a s e s r a p i d l y w i t h f u r t h e r i n - c r e a s i n g Nb c o n t e n t . Such a Nb c o n c e n t r a t i o n de- pendence

i s

s i m i l a r t o t h e tendency /15/ noted f o r c r y s t a l l i n e Ti-Nb b i n a r y a l l o y s , s u g g e s t i n g t h a t t h e electron-phofion b a r e d e n s i t y of s t a t e s a t t h e Fermi level(Ef=O) N(O), t h e electron-phonon coupling con- s t a n t

X

and t h e Debye t e m p e r a t u r e

e

which p l a y a n important r o l e i r . d e t e r m i n i n g Tc /16/ change s i g n i f - i c a n t l y i n t h e r a n g e of 40-60 at.%Nb. The h i g h e s t Tc v a l u e i n t h i s system i s 5.5

K

f o r t h e Ti45Nb40 SiloB5 a l l o y .

The T, v a l u e s of Ti-Nb-Si and Ti-Nb-Si-B amor- phous a l l o y s a r e p l o t t e d a s a f u n c t i o n of t h e aver- age e / a of t h e t r a n s i t i o n m e t a l components i n F i g . 5, wherein t h e d a t a of t h e Nb- and Mo-based, amorphous a l l o y s o b t a i n e d by t h e p r e s e n t a u t h o r s / 5 , 6,11/ a r e a l s o i n c l u d e d and compared w i t h t h e v a r i a - t i o n of Tc f o r amorphous t r a n s i t i o n m e t a l s o b t a i n e d by C o l l v e r and Hammond /14/ who employed t h e tech- n i q u e of t h i n f i l m e v a p o r a t i o n on a c r y o g e n i c sub- s t r a t e . From t h i s f i g u r e , i t

i s

s e e n t h a t t h e v a r i -

Average electron concentration

,

e l a F i g . 5 T r a n s i t i o n temperature(Tc) v s . e l e c t r o n p e r

atom r a t i o f o r t h e Ti-Nb-Si and Ti-Nb-Si-B amorphous a l l o y s . Also, t h e d a t a of Nb-Si, Nb-Mo-Si, Nb-Zr-Si, Nb-Si-B and Mo-Si-B amorphous a l l o y s a r e r e p r e s e n t e d by s o l i d c i r c l e s .

a t i o n of Tc w i t h a l l o y composition f o r each a l l o y system

i s

r e l a t e d a p p a r e n t l y t o t h e a v e r a g e e / a . Johnson e t a l . /17/ have shown f o r (Mo-Ru)8oP20 amorphous a l l o y s t h a t such a change of Tc w i t h e / a corresponds w e l l t o t h e change of t h e N(0) w i t h e / a .

It i s

a l s o t o b e n o t i c e d t h a t t h e Tc v a l u e s of t h e Nb- and Mo-based a l l o y s l i e below t h e C o l l v e r - Hammond curve. The o b s e r v a t i o n t h a t Tc v a l u e s of melt-quenched a l l o y s l i e below t h e Collver-Hammond c u r v e was a l s o n o t e d e a r l i e r f o r Mo- and Zr-based a l l o y s 117-20/. T h i s i m p l i e s t h a t when t h e t r a n s i - t i o n m e t a l components i n t h e a l l o y s a r e widely sepa- r a t e d i n e / a a n d / o r t h e a l l o y s c o n t a i n m e t a l l o i d elements, t h e Tc t e n d s t o f a l l below t h e C o l l v e r - Hamnond c u r v e f o r m e t a l s and a l l o y s of n e i g h b o r i n g m e t a l s . On t h e o t h e r hand, t h e Tc v a l u e s of Ti-Nb- S i and Ti-Nb-Si-B a l l o y s a r e above t h e C o l l v e r - Hammond curve. A l t h o u g h , t h e r e a s o n f o r such

a

d i f - f e r e n c e i s u n c e r t a i n a t p r e s e n t , i t s o r i g i n may b e found i n one o r b o t h o f t h e f o l l o w i n g two f a c t o r s : (1) t h e mixing of t h e m e t a l elements from d i f f e r e n t t r a n s i t i o n m e t a l s e r i e s , and (2) t h e oxygen c o n t e n t . P r e v i o u s i n v e s t i g a t i o n s /18/ and o u r p r e s e n t r e s u l t s ( F i g . 3 a ) show t h a t mixing o f two o r more m e t a l elements from d i f f e r e n t

series

r e s u l t s i n a d e c r e a s e of Tc of amorphous a l l o y s . On t h e o t h e r hand, i t h a s been r e p o r t e d /21/ t h a t a s m a l l amount of oxygen can s i g n i f i c a n t l y r a i s e Tc o f c r y s t a l l i n e Ti-Ta a l - l o y s . Thus, i t i s p o s s i b l e t h a t t h e Tc h i g h e r t h a n t h e v a l u e expected from Collver-Hammond c u r v e may b e due t o a s m a l l amount of oxygen c o n t a i n e d i n t h e Ti- Nb-Si and Ti-Nb-Si-B amorphous a l l o y s . It

i s

hoped t h a t s y s t e m a t i c i n v e s t i g a t i o n s , c u r r e n t l y i n prog- r e s s , on t h e e f f e c t of oxygen o r n i t r o g e n on Tc w i l l shed some l i g h t on t h i s problem.

2-2. C r i t i c a l magnetic f l e l d ( H , ) and c r i t i c a l c u r r e n t d e n s i t y (J,)

The lower and upper c r i t i c a l magnetic f i e l d s , H c l and Hc2 were measured a t l i q u i d helium tempera- t u r e by a s t a n d a r d four-probe r e s i s t a n c e method.

The Hc2(onset) and Hcl(overall) v a l u e s o b t a i n e d a r e 4.9 x

lo6 ^A/m

and

1.1

x

lo6

A/m f o r Ti55Nb30Sil2B3 and 6 . 1 x 106 A/m and 8.8 x

lo5

A/m f o r Ti45Nb40 Sil2B3, f o l l o w i n g t h e g e n e r a l tendency 1221 t h a t t h e h i g h e r t h e Tc, t h e h i g h e r

i s

Hc2. A d d i t i o n a l l y , one can n o t i c e t h a t t h e Hc2.values a r e much h i g h e r com- pared w i t h t h e

H c l

v a l u e s . T h i s l a r g e d i f f e r e n c e h a s been c o n s i d e r e d t o b e due t o t h e l a r g e Ginzburg -Landau parameter / 2 3 / . These r e s u l t s i n d i c a t e t h a t

t h e p r e s e n t amorphous a l l o y s can b e c l a s s i f i e d a s t y p e

I1

s u p e r c o n d u c t o r s .

The c r i t i c a l c u r r e n t d e n s i t y

Jc

was measured a t e x t e r n a l a p p l i e d magnetic f i e l d ( H ) i n a l i q u i d h e l i - um b a t h . F i g u r e 6 shows t h e c r i t i c a l c u r r e n t densi- t y

Jc

a s a f u n c t i o n of

H

f o r Ti55Nb3oSil~B3 and Ti45 Nb40Sil2B3 amorphous a l l o y s . For H=O,

Jc

i s found t o b e about 450-480 ~ / c m ~ . For

H>O,

Jc i s observed t o f a l l v e r y r a p i d l y w i t h i n c r e a s i n g H . For exam- p l e , a t H=3.2

x

106 A/m(40 kOe),

Jc

i s of t h e o r d e r 220 ~ / c m ~ . Such s m a l l v a l u e s of

Jc

i n d i c a t e t h a t f l u x pinning f o r c e s i n t h e s e m a t e r i a l s a r e compara- t i v e l y weak.

H

(kOe)

10 20 30 40 50 6D 70 80

Hc2 (onset )

,

20

.- 8

.. t

O 0 1 2 3 4 5 7

Magnetic field. H (Alrn) ^''06

Fig. 6 C r i t i c a l c u r r e n t d e n s i t y ( J c ) of Ti55Nb30

Si12B-j and Ti45Nb40Si1.2B3 amorphous a l l o y s a s a f u n c t i o n of magnetic f i e l d a p p l i e d normal t o t h e d i r e c t i o n of c u r r e n t flow.

The superconducting p r o p e r t i e s ( T c and Hcp) of t h e amorphous a l l o y s c h a r a c t e r i z e d i n t h e p r e s e n t i n v e s t i g a t i o n a r e , w i t h i n t h e a u t h o r s ' knowledge, t h e h i g h e s t f o r d u c t i l e amorphous a l l o y s showing complete bending, b u t a r e

s t i l l

i n s u f f i c i e n t f o r p r a c t i c a l u s e . From t h e t e c h n o l o g i c a l p o i n t of view, however, liquid-quenching makes t h e p r o c e s s i n g of superconducting m a t e r i a l s much s i m p i e r . Espe- c i a l l y , t h e e x i s t e n c e of a r e a d i l y o b t a i n a b l e amor- phous phase i n t h e Ti-Nb-Si and Ti-Nb-Si-B systems and t h e r e s u l t /7/ t h a t t h e superconducting proper- t i e s of t h e s e amorphous a l l o y s improve remarkably on c r y s t a l l i z a t i o n o f f e r a l t e r n a t i v e means of f a b r i c a t - i n g superconducting t a p e s o r w i r e s . I n f a c t , Ti-Nb- Si-B a l l o y s c o n s i s t i n g of a duplex s t r u c t u r e of amorphous and c r y s t a l l i n e phases show superconduct-

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i n g p r o p e r t i e s much s u p e r i o r t o t h o s e of ' c o m p l e t ~ l y

amorphous a l l o y s w i t h o u t a d e t e c t a b l e l o s s of duc-

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