PROPERTIES OF Nb3Ge TAPE SUPERCONDUCTOR PREPARED BY CVD METHOD

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PROPERTIES OF Nb3Ge TAPE SUPERCONDUCTOR PREPARED BY CVD METHOD

V. Černuško, K. Fröhlich, M. Jergel, D. Machajdík, M. Tarnovská, V.

Fedorov, P. Cheremnykh

To cite this version:

V. Černuško, K. Fröhlich, M. Jergel, D. Machajdík, M. Tarnovská, et al.. PROPERTIES OF Nb3Ge TAPE SUPERCONDUCTOR PREPARED BY CVD METHOD. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-429-C1-432. �10.1051/jphyscol:1984188�. �jpa-00223744�

JOURNAL DE PHYSIQUE

Colloque C l , supplément au n° 1, Tome 45, janvier 19Sf page Cl-429

PROPERTIES OF Nk>3Ge TAPE SUPERCONDUCTOR PREPARED BY CVD METHOD

V. Cernusko, K. Frohlieh, M. J e r g c l , D. Machajdlk, M. Tarnovska, V.K. Fedorov*

and P.A. Chereranykh*

Electrotechnical Institute CEFR, Slovak Academy of Sciences, 842 3$ Bratislava, Czechoslovakia

*I.V. Kurchatov Institute of Atomic Energy, Moscow, U.S.S.R.

Résumé - Nous avons étudié las propriétés de rubans supracon- ducteurs de NboGe, préparés par la méthode de CVD, dans les ohamps magnétiques jusqu'à 19 T. L'analyse au rayonnement X a été utilisée pour déterminer les phases de la oouche supraoon- duotrice. Les propriétés de nos rubans sont oomparées avec les résultats obtenus ailleurs,

Abstract - The p r o p e r t i e s of tape Nb.Ge superconductor prepar- ed by CVD method i n magnetic f i e l d s dp t o 19 T were s t u d i e d and X-ray phase a n a l y s i s was performed. The p r o p e r t i e s of our oonductor are compared w i t h r e s u l t s obtained by other l a b o r a - t o r i e s .

I. INTRODUCTION

To produoe the Nb-Ge superconductor few methods are used in order to prepare short samples. For preparation of long continuous tape the well-known CVD method is used. The Nb~Ge conductor of lenght of about

lO m to 150 m was prepared by this method in various laboratories and also at our Institute p , 2\ , of course differences exist as far as the technological details are concerned. It is the purpose of this contribution to report on the properties of our Nb„Ge tape supercon- ductor prepared lately by CVD method at our Institute.

II. EXPERIMENTAL

1. Sample preparation

The apparatus used has already been described,in one of our previous papers Q Q . T o prepare the Nb and Ge chlorides, the niobium of 99« 95 wt./& purity, germanium of eleotronio grade, and gaseous chlorine of

technical purity have been used. As a substrate we used the Cr/fri- steel tape with dimensions 3 x 0.05 mm . The speed rate of the moving 2 tape was 20 m/hour. The following parameters were optimized: the rate of the reaotion mixture flow, the substrate temperature and, the Nb/

Ge ohlorides ratio. The reaotion ohamber-wall temperature during the deposition prooess was held at 450°C. 3 to 15 samples, 1 m in lenght each, were prepared during one experiment.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984188

CI-430 JOURNAL DE PHYSIQUE

2. Sample measurements

The critical ourrents were measured in transverse magnetic fields up to 19 T with the field veotor parallel and perpendioular to the broad side of samples. The oritioal temperatures were measured by the stan- dard four-point resistive method also in parallel and perpendicular magnetio field. The X-ray phase analysis was performed by the HZG-4 dif ractome ter.

111. RESULTS

The dependences of critioal ourrent lo and oritical ourrent density Jc upon magnetic field value B for one of our better samples are il- lustrated in Fig. l.

Ms. 1

-

-

Tfie dependenoe of critioal temperature Tc on ma-etic field for the same sample as in N g . 1 is plotted in Fig. 2. The dependence is li- near in whole range of magnetic fields.

The validity of ICramervs scaling law has already been verified also for NbgGe samples prepared by CVD. Up to this model, the pinning for- ce density F may be written in case of a constant temperature as

P

and by rearrangin@;:

where b = B / B ~ ~ , Bc2 is the upper critioal field value, Ks is the flux line lattice shearing parameter, and A is the coefficient inde- pendent on B. The Bc2 (2) value obtained by this method refleots an a- verage property of the superconducting layers and nay reach lower value than the real upper critical nagnetio value

b,

3 ' 0

Bc2(T = 0)

=

=

(3) value calculated from eq. 3 characterizes thin superoonduc- B02

ting layer with the best properties. For series of five Nb Ge samples 3

the extrapolated Bo2 values for T P 4.2 I( lay in the regfon from 22.8 T to 28.4 T, the extrapolated

%h3)

05T2

for B,, orientation, (2.4 to 3.6)x109 ~ / m for BI orientation and, the value of JolST is (3.9 to 7.7)x10 8 ~ / m 2 for B,, orientation and (3.2 to 5.2)=10 8 A/m2 for the BL orientation.

The layer thiakness of the investigated samples is 4.5 p u to 7.0 )M.

The Nb3Ge pbase oontent has been found to be 60$ to 95% with the rest being hexagonal N b G e phase. It is of interest to notioe that this phase is not dispersed throughout the volume of deposited layer homo- geneously. The amount of the hexagonal phase is 5% to 1 0 $ closely to the substrate surface, rising to the value 25% to 3 6 towards surface of the deposited layer. Some samples have even 1 p m to 2 )un thiok pu- re hexagonal phase surface layer.

The ohemioal oomposition obtained by EDAX-analysis has shown that the Ge-oontent is inoreasing in the direction eubstrate+layer-surfaoe from about 16 wt.$ to 18 wt.$ at the substrate up to about 3 0 wt.$

at the deposited layer-surface with the rest being ZUb. The results of this element analysis have oonfirmed conclusions of the phase ana- lysis c o n c e ~ the nonuaiformly soattered hexagonal Nb-Ge phase throughout the deposited layer.

The lattice parameter of the investigated samples xas 0.5144 nm to 0.5148 nut. The I/;! width values of the 004 diffraotion sre from the interval (0.43 to 0.52) O2

8

C 1-432 J O U R N A L D E PHYSIQUE

thickness of the deposited Nb-Ge layer.

Properties of the Nb3Ge su-

M g . 3

-

rati is lava,

peroonduotor prepared by CVD by other produoers are compa- red i n Fig. 3. Also proper-

ties of already oommeroially produced teohnioal tape su- perconduotors Nb S n and V Oa

3 3

are inserted into this diag- ram. The Jo values for B

<

3 rial as that of diffusion- prooessed Nb S n tape produoed

3

cotllmeroially for instanoe i n

KbBU) Bratislava, but they are so far still lower than

the values for doped composi- te-prooessed V Oa tape [6].

3

IV. CONCLUSION

Properties of the Nb3Ge tape superoonductor prepared by oontinuous C M method are desoribed and compared with results obtained by other laboratories. The Jc values up to 7 . 7 ~ 1 0 ~ ii/rn2 in 1 5 T / 4 . 2 K a n d , t h e Bc2 values up to 35.4 T/O K were obtained. The layer thiohess of the deposited layer was 4.5 pm to 7.0 pm, the value of lattioe parameter was from 0.5144 nm to 0.5148 nm and, the content of the Nb Ge phase

3

was 60 w t . $ to 95 wt.5. $.e hexagonal N b - G e phase is nonuniformly dispersed within the deposited layer. Further improving in Jo is on the way.

Ref erenoe s

dEZWUSI(0 V., JERGEL M. and ~ A B E I ~ ( A D., Solid State Co~mn.

a

Magn. MAG-12 (1981) 2051

[3] THOMPSON J.D., W Y M.P., NEUKlRK L.R. and BdR1E1T R.J., J.*PP~.

Phys. (1979) 977

bl

,

,

[5] V I W E E W G R N.R., W A N D E. and HORE*NBERG P.C., m a . Rev.

&!

(1966) 295

[6I TACHM~WA K., TB;NAI(~ Y., YOSHIDA Y., ASNO T. and IYASA Y., IEEE Trans. Hagn. M A E 1 5 (1979) 391