Behaviour of Nb3Sn multifilamentary wire with H additions

Behaviour of NbsSn multifilamentary wire with H additions C. Ferdeghini, M. Ferretti*, F.C. Matacotta'l, C. Rizzuto-t- and A. Siri:l: G N S M / C I S M and Diparl.mento dl Fislca, Via Dodecaneso, 33 Genova, Italy *lstltuto di Chimica Fisica, Genova, Italy l"lst.tuto d. Metrologia 'G. Colonnettf, Tar.no, Ilaly t G N S M / C I S M and Istituto d~ Fislca di Ingegneria, Genova, Ilaly Received 4 June 1984 The presence of interstitial hydrogen in the A15 structure of Nb3Sn affects its superconducting properties. This Paper reports the effect ol Ihe addition of hydrogen on Ihe superconducting performance of a Nb3Sn multifilamentary wire. Thermodynamic properties (Ihermal conductivity and specilic heat) are also delermined in order to invesllgate the effect of the doping on the stability of the wire. Keywords: superconductors; multifilamentary superconductors; Nb3Sn; thermodynamic properties; hydrogen doping

The addim)n of small quantities ol a third elemenl (interstitial or substtluttonal) tn the AI'~ structure of NbjSn inhibits, in some cases, Ihe telragonal martensillc Iranslormalion which occurs al43 K in the bulk malenaP and affecls Ihe superconduclmg properhes ol Ihis malerial. Inlerslilial hydrogen is one of Ihe possible elemenls and il seems sutlable for superconduclor Irealmenl because hydrogen doping can be performed as a last slep of Ihe producllon of a superconduclmg (so) winding, wllhoul any olher change in the wire processing In a previous paper" the existence ol maxima m fhe T,. and J,: corresponding Io hydrogen concenlrallons below ().0S Ibrmula units (FU) ( 1.2 t a¢'A)),was polnled out In this Paper Ihe besl hydrogen concentrallon(in order Io maximize s c. perlbrmances) is delermmed and data un specific heat and thermal conducllvi .ty are presenled

Hydrogen doping Nb~Sn wire (Vacryllux NS~700, produced by Vacuumschmelze, Hanau) has been used In this work This is a ().~ mm diameler bronze wire with .~F7IN) filaments of onginally unreacled nll}b,urrl U shaped samples, 40 cm long, wrapped in lanlalunl foil were reacied under vacuum (P, Ill -~ loft) al a lemperalure of 'I(}()+Y'C lot 04 h, as prescribed by Ihe manufacturer. We tested two ways of introducing hydrogen into Ihe samples' I admlrting H~ gas m the furnace al '1(}()"C dunng Ihe reacllve Iormalton of Ihe AI5 phase, 2 admirhng Ht gas d u n n g an anneahng step al a lower lemperalure after the reactnon We Iound that the second method allows a better conlrol of Ihe doping process, the annealing, temperature being, ,~=,40()"C (a compromise between the besl Ihermodynamic conditions Ibr Nb~Sn hydrogenation and Ihe poor diffusion of hydrogen in bronze at lower letup O0 'I I -22 75/'85/(.)40208-(.34 $03 O0

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Cryogemcs 1 9 8 5 Vii 2 5 April

eralures) Keeping, Ihe Hz pressure at ()1 MPa Ihe hydrogen conlent in Nb,SnH, increases when the annealing lime is increased. The conlent ~ (expressed in formula units, FU) is determined by measuring lhe vanallon of lhe laLtice parameler, a, lhrough X-ray diffraction pallerns from powders extracted from the wire, following Ihe model proposed by Machlm 'l T'he variation of a and ~ versuslhe annealinghme is shown in Fig I (On Ihe left nrdmate the latlice parameter increase, ~ , on Ihe nghl one the hydrogen content are shown) Short annealing limes decrease Ihe reproducibilzLy of hydrogenali(m Thts is probably due to Ihe adsorption that takes place dunng the furnace coohng We were unable It}cool down al a speed ~'eater than R)'C rain -I. 'This lack of accuracy in Ihe low H concenlralion region could be avoided by reducing the annealing temperalure or fhe lime conslanl oflhe oven syslem. In the lirsl case (as can be seen from the poinl labelled 31)()"C in Flg I) the required annealing, Izmes are correspondingly longer We checked I m h)ng samples for homogeneity Ihe H concentramm is conslanl along Ihe wire excepl Ibr a small hwal~zed gradienl al Ihe ends of the samples.

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200

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Effect ot hydrogen on superconducting performance ot Nb:~Sn: C Ferdeghini el al The H diffusion m Ihe composile, Iherelk)re, takes place radially Ihrough Ihe bronze.

Nh w,l.mHI ) ( I ', ~(.)()

Critical current m e a s u r e m e n t s Reacled and doped samples are inser'led ,n a C)FHL" copper sample-holder equipped w,lh a res~sl,ve healer and a carbon glass Ihermomeler. The shape of Ih,s holder ,s tdenltcal to Ihal used Ior Ihe reacl,on and hvdr~ genalton h.) mtntmtze stress effecls Eleclncal tnsulaliun and Ihermal conlacl are provided by (..iF. '711~,1 varntsh and stl,cone grease respeclwely The sample-holder ,s mounled ,nside a vacuum cryoslal in Ihe bore ~1' a 12 'T' magnet The heal mpul due Io current leads and Ihe restslwe dJsstpal,on are dumped inlo Ihe exlernal4He bath Ihrough a low pressure '~He almosphere ma,nl.atned m Ihe cryoslal. 1'he sample h(dder temperature can be eonlndled w]lhin a lew lenlhs ol Kelvin by sell,ng Ihe healer currenL The carbon glass Ihermomeler sh~)ws slahle behavlour in Ihe rnagnellc f'=eld Electneal leads fur w.)llage deleclton are soldered on Ihe sample solhal Ihe porl~on ol mon,lored w=re( ~: 4 cm) ts nearly perpend,cular to Ihe field. The appearance of '~ y.V between these leads ts laken as the Iransilton p~qnt Th,s c o r r e s p o n d s Io defining a Iransiliun when Ihe s a m p l e res,sl,vi .ty b e c o m e s II) - ~ - I0 - ~ Elm d e p e n d m g ~n Ihe I value. 'The overall c n l i c a l currenl d e n s , v ,s m e a s u r e d m Ihe ranges 4.2-10 IC ~-12 'T and h)r hydrogen c~m. c e n l r a l i o n s ranging up lu ILl 14 FI.J. 'The overall cnllcal currenl denstltes versus hydrogen conlenL al vanous lemperalures and al a field ()1 12 T, are shown tn F~g 2 A prunounced maxtmum ,)l J, =s observed al all lemperalures Ior an hydrogen conlenl ol 0.()3 F'LI For increasmg hydn)gen eonlenls Ihe values olJ,. fall below those of the 'blank' s a m p l e s 'T'h,s hehavu.~ur Is ma,nlamed al any field in the observed range

,.+ I~)(1 o_

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t'l8 I shows Ihe relat,ve varlalton ~)1 Ihe cnllcal currenl ~)1 Ihe Nb~,.'Sn I~j,j sample relaltve h.) Ihat ~bl Ihe u n hydrogenaled sam pie, as a fu ncl,~)n of lem peral u re, h Dr a fieldB = 12 T The increase In perlormance~)l'lhe wtre,s more pronounced al h,gher lemperalures wtlh a J,. gain ~1 up Io 21 ",% al I() K 'T'hls behaviour ,s ,mp()rlanl Ior wire slahlhl3' constderal,ons, because II c~)mpensales Ihe lower heal Iransporl capab,l,ry ,n +,.'ase~1 ao.'tdenlal healtng ~1 the wire ']'he simtlar hehavil)ur ()1 Ihe cntwul lemperalure TI ,~) is shown m FLt; 4

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Three methods are t.'ommonlv used h~,r spectl'le heal measuremenls I adiahalic ~r semtadiahal,c measutemenls 4, '~ ,Jlh1111Ull ~I' a slnus~),dul e x c l l a [ l ( ) l l ver',;us Irequeru.3,~, ~i tnd,rect melh~)ds (measuremenls ol c~mdueltvtl~ and dtllus,vil3')* The firsl two) melhods need lhermal equ,l,hr,um c()n dimms and are hesl sutled lor hulk samples, ,flhe samples are h)ng Ihm w,res ~)la c'omp()slte material, Ihe Ihlrd melhod seems Io he Ihe hesl approach Thermal conducl tvJlV and dtflustvt .ly have Ihereh)re been measured and Ihe

CryogenJt:s 1985 Vo125 Aprd

209

Effect o/hvdrogen on superconductmg performance ot Nb:jSn: C. Ferdeghin/ el am Seen hydrug.enaled al dil'l'erenl coneenlrations 'These curves show a 'llal' Nh,Sn superconducUng Iransmlm()n al 4 ,%1

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'.-)(2

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C/T versus f 2 curve Ior a sample ol non-reacled wire

,,.,pecll~c heal is g,wen by the rallo between Ihese two quanlHle,s Our mea,sunng melh~)d i,s based on Ihe observed relal.~mship belween Ihe F'~mrler Iranslorms ol the mea,sured lemperalure c)n Ihree eqmdislanl pl)inls along Ihe ,,;ample ,sublecled h) ,', pen(~d..' eXcllal..m and has heen reporled mn dcla,I in u prev..~us paper" Sample.'`; ol sull'wienl secl.m are i)blamed by usm~, Iour parallel pmeces ol wire '~ cm long and '.,~)ldenng, h)tJ,elher Ihe=r ends by dipping .n a liquid lin balh A manganine heater(R = .",(X)~)is atlached by (..;E varnish al one end ol Ihe bundle 'T'hree ddl'erenl.al Iherm~) o)uples are Ihermally connecled al a distance o i l cm Irom each olher ahmg Ihe bundle, the Ihermal conlacl be=ng, provided by GE 7()tl varn.sh 'The accuracy ol specmllc heal measurements ms belier than l"/,, F'tg i shows lhe (./T versus '/~ curve fur a sample ol non-reacted w,re 'The specd'=c heal should be, m l~rsl apprux,mali~m, a Welghled average oI" lhe specd~c heals of lhe components ol lhe wire(i e. Nb and Cu 11.h wt% Sn) A.n analvsls ol the phomm and eleclron contnbulions conl~rms, al least for 'r ' 'l"~, Ihls hypolhes~s ~Jso Ihe dmsc()nlmnuiW o1' Ihe specil'w heat al Ihe Irans,l,m ol Nb has Ihe expected value. F'Hling. Ihe dala Io a T ~ behav,our gwes Debye lemperalure value.'`; of 0 D = 27", K and ~r~ = 2N0 K respecl,vely For Nb and CuSn 'The ratiu be~een the C/T d,scunl~nuHy al T~. Ibr Ihis mullifilamenlary cable relalive lu Ihal ol a pure Nb sample is equal to ()2h, ,n good agreement with Ihe w)lume rat,o ol Nb ,n the cable An an~)malous behaviour ~s, inslead., observed when Ihe ,nlercepl ol' Ihe high lemperalure L~T' values exlrapolaled Io zen) lemperature ,s considered IIs value is too high Io be .'`;imply atlnhuled Io Ihe sum Ior Ihe Nb and Sn 7 values Also the enlrupy in Ihe supcrconducUng slale, evalualed up h~ 'r,, is lower Ihan Ihal exlrapolaled I'r~)m Ihe normal stale data 'The dashed curved ,n Frg i gives equal enlrupies lor lhe superconduclm[-~, and nurmal stares at '/'( and conlemporarily t-',,vesa value ol 1' for lhe mulu61amenlary wire wh,ch at~',rees w~th a weighled average ~)I"I' for the constltuent.s 'Thms behav.mr IS smm~lar h~ Ihal reporled in IHerature4 lot Ihe AI~ slruclures, bul ~n Ihls case Is found lot a non reacled Nh A possible explanallon of Ihls behavlour c()uld be reierred Io a Iowermn~ ol the sound veh)cml~, assocmaled Io Ihe compressmon ol Nb I',laments F~g h shows c / r versus 'r ~ h.)r #our reacled Nb~Sn sample.,,, ~# whmch three have

210

Cryogenics 1 9 8 5 Vol 25 April

[ "" 17.h K. 'T'h,s Iransilion shape Is an agreemenl with the Iileralure 7 'T'wo more IransHions show up One, al aboul ~-~ K.. msdue to the unreacled nl~htLIm mn Ihe core of Ihe I'flamenl,s ( = h w1%), while Ihe other, al ~: II K (reported als~ in uther papers ~) has still Io be completely explained Fig 7, where Ihe lemperature scale is expanded hi belier sh~lw the low lemperalure behavlour, shows evmdence Ior ()lher IranslllOns. Not all experimenlal pomnls are rep~)rled., Ii) alh)w a clearer vmew, in Ftg,,,: h and 7 The (/T',sh)pe oblamed in Fl~ 7 Ior the vanous .'`;ample.'`;Ior Ihe h)we,sl lemperalures ( ': 2 K), which should represent Ihe phi)non conlnbutmon It)C. IS hi~,her than thai observed al hmgher lemperatures From the expermmenlal dala we can therelore summarize Ihe h.dlow=nF, erlccts caused by Ihe addition uf H I an important .,,;hill ol Or)(the Debye lemperarure) It)wards hmL:,her value.'`; which gmves lor Nb~Snl-~, ,,, a specidc heal reduced Io I/2 ol thai lot n(mhvdrogenaled w,re, ab~we I1) k. In parlicular Ihe,8.,....,ll (7" ~coel'f'..'ienl mJ cm -~ K -'=) vanes hetween 0()1()5 for Ihe ram-hydrogenated wire to ()(HI",() ior NbjSnl-~ ~,~ 'T'his large ellecl is due Io Ihe higher packing of Ihe aloml¢ [alllce due Io Ihe presence o1" H

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C F e r d e g h m t el al

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200

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We have shown a simple and qulh: repealable methitd lilt NblSn mullll'ilumenlarv wire hvdrogenalilm The inlet p r e l a l l o n ()1 Ihe resulls ciblalned in Ihe hghl ul p~lsslble

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apphl.'ali~lns is eqtiiw..'al II is, ii1 lack possible hi raise Ihe critical c u r r e n l ~fl' Ihe wires bul Ihe useful I h e r m a l p n l p e r i i e s (heal capacil~, and I h e r m a l cllnducllvll~/) are reduced s ~ ) I h a l Ihe hydrogenated wire has a h)wer

~.1%h

11 I~ll

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I

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1

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I0

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20

slablhly 'T'hm drawback could be cornpensalcd by inserling addllu.lnal slahlllzallcm in wires, hl lake advantage ol the very high J, values al higher lemperalures

r(KI Fig. 6 Thermal conducl.vily versus lemperalure unreacled, reacted and hydrogenaled samples

Ior

the

2 a reduction el Ihe specific heal j u m p al the Nb~Sn Iransilions. A rough eslimale gives AC/T, "-" "t2 n'LI g a l - I K -~ Ior NbiSn and AC/7":--- 12 ror NhiSnl-le ll4 This may ind,cale a lower 7 = L'n/'T value t a slight, bul imporlant, shill ol'T~ wh,:h increases h.lr low hydrogen ccincenlralions in a g r e e m e n l w l l h the reSlSllVe IransillOns (ll F~j~ 4 In Fig ,~ we report Ihe b e h a w o u r o l ' l h e I h e r m a l o m d u c l w i l y K as a f u n e l l o n el l e m p e r a l u r e Some aspects hJ be remarked el these curves are Ihe hllh.lwlng I Ihe unreal:led wire ( N b + t ' u - 1 3 '~",,, Sn) .shows u p r o n o u n c e d Ilex the tlllihlLIITi conlribulmn hi K is Iherelore d o m l n a n l

Ihe Ihermal c~lnduchvlty ill Ihe reacled wires is nearly linear Ihe d o m i n a n t lerrn is Iherel'clre I'rom Ihe bronze (which has a lower lin ccinlenl because o1' Ihe AI'~ h.lrmailtm) while the NbiSn cry. sial stale is rich in delecls.

Acknowledgments We wish IO t h a n k A. Del 'T'urco (SISR.AM) hir i i a v i n g kindly supplied Ihe superconduch.lr and Pr(ffessur (.; Bruz, zone for helplul advice. F'undlng Ibr Ibis research has been oblained Ihrough Ihe G r u p p o N a z m n a l e dl Slrullura della Malerla o I ' C N R ( G N S M ) and by Ihe Mmlslr'y ol Pubhc Inslrucllon I h r o u g h Ihe C'enlro I n l e r u n i v e r s i l a n q l di S l r u l l u r a della Maleria (CISM)

References I

F'lukller, R..4dr ~ rl,r,g t',g l lq~?) 28 tu'-)

2

and Bruttone, (., I / / # Tram ,4/u,t;. i IqX tl MAG- Iq Nq7 Machlin, E',.S. ,4ct. ,Ih'tllq74) 2Z qil Junod. A., Jarlborg, '[' and Muller, J Phr~ Rm' llqNll B !? I "ltiX ,.Nlewart, C; R. Rl,i, ,.%'l'lI#l.~lrm.ii (IqNt) ~ i ~ln, A., 5 i ~ l , (.;., Vlli'calone, R., FernandeL, P. and ~aho, 1.' /'~ocll t ~ 7, IP(. bi.ieril'e ,irid 'IL'L luu,lilI,y Pre~,,., I_;ulh.lhlid I_lK (lU7H) F'lukl~er, I1., 8ehauer, W, Specking, W. and (Jdd~ L ,4dr ~ mJ~r

t 4 ', tp 7

Malat'oila., l'.(.'., I;'erdeghinl, C., Ferreflt, M

# .g (IqN2) ,!8 'i61

Corrigendum Effects i)l Iranslenl heal transler hi liquid helium on steady pr=~pagalmn veloc=ty ol m)rmal zones ~n super conducllng wires, K. F'unaku F' Ine, M 'T'akeo, U. RupperL K L.uders and (3 Khpping Crl,ogemcv (IqN'~) 25 I lq- 1.4'~ Equalliul (Ill) shctuld read

(=')l(#)

-- - ~1',

it I'

~,= u '

r%

it'r exp[-i ,'~/4u,(/-.l') I ds ] it,~-T " () - s)'/'

Cryogenms

l

1985

Veil 2 5 A p r i l

p: 0

211