Volume 133, number7,8 PHYSICSLETTERSA 28 November1988

THE EFFECT OF Pb ADDITION ON THE STRUCTURE AND THE STABILITYOF SUPERCONDUCTING PHASESIN Bi-Sr-Ca-Cu-O SUPERCONDUCTORS

Qing HE, Ding-An YU, Shi-An CHANG, Rui-Kun WANG and Hong ZHANGDepartment203, GeneralResearchInst ituteforNon-ferrousMetals,Beijing100088,PRChina

Received11 August 1988;acceptedfor publication5 September1988Communicatedby J.I. Budnick

A superconductorwith zeroresistivity temperature104 K hasbeen preparedby incorporatingPb into theBi—Sr—Ca—Cu—Osuperconductor.ThePb additiondoesnot changetheunit cellparametersofthesuperconductingphases,but it enhancesthehigh-temperaturestabilityaswell astheproportionof thehigh-T,phase.The chemicalcompositionsof low-7’~andhigh-T,phasesareapproximatelyBi

4Pb1Sr4Ca2Cu4O~andBi4Pb1Sr4Ca3Cu6O~,,respectively.

1. Introduction 2. Experimental

Following the discoveryof (La1_~Ba~)CuO4with Thesampleswere synthesizedby typicalsolid statea T~of 30 K [1] and the 90 K superconductor, reactions.SampleA hada nominalcompositionofYBa2Cu3O7_~[2,31, a newhigh-Taoxide supercon- Bi1Sr1Ca1Cu2O~.Appropriate amountsof Bi203,ductorwithout a rareearthelement,Bi—Sr—Ca—Cu— Sr(N03)7, CaCO3,all 3N pure, were thoroughly0, hasbeensynthesized[4,5].It is knownthat there mixed andgroundin an agatemortar.Themixtureare at leasttwo superconductingphaseswith a T~of washeatedin air to 1113 K for 24 h, regroundand110 and85 K respectivelyin the Bi—Sr—Ca—Cu—O pressedintopelletsat a pressureof 14.7kbar. Twice,superconductor.It hasnotyet beenpossibleto com- the pelletsweresinteredin air at a temperaturebe-pletely separatethe high-Taphasefrom the low-Ta tween1123 and 1153 K for 24 h, followed by an-one so that thereis usuallya residualresistancein nealingat 773 K for 24 h andthenfurnace-cooling.the Bi—Sr—Ca—Cu—Osuperconductoruntil the low- SampleB, with a nominalcompositionof Bi 1Pb0.18-T~phasebecomessuperconducting.Sunshineet al. SrlCalCu2O).,was preparedby mixing PbO (4Nreportedthata T~of 107 K wasobservedby mag- pure) with powderedBi1 Sr1Ca1Cu2O~,which hadnetic susceptibilitymeasurementin a Pb-substituted beenprefiredat 1113 K for 24 h, firing, pressingandBi—Sr—Ca—Cu—0sample[6]. sintering at 1123 K for 24 h followed by furnace-

We havedevelopeda two-stepprocessto synthe- cooling.size a superconductorwith a zero-resistivitytransi- Thephaseanalysiswasmadeby meansof X-raytion temperatureT~0 104 K by incorporatingPb andelectrondiffractionusinga RigakuD/MAX-RCinto the Bi—Sr—Ca—Cu—0compounds.Experiments X-ray diffractometerandJEM-2000FXtypeanalyt-were carriedoutto comparethe structureof the su- ical electronmicroscopeequippedwith anEDX sys-perconductorwith Pbandthatwithout Pb. It is found tern.The micrographsweretakenby usingaJSM-840that thePbdoesenterinto thelattice of the newsu- scanningelectronmicroscopewith anEDX system.perconductor,andenhancesthe stability and pro- TheTG andTDA measurementswerecarriedoutinportionof the high-Taphase. a Rigaku DPS-8150 thermogravimetricand differ-

entialthermalanalysisequipment.Theresistivityandacmagneticsusceptibilityweremeasuredby thetyp-ical four-probemethodandmutualinductancetech-

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Volume 133, number7,8 PHYSICSLETTERSA 28November1988

nique, respectively. High temperature X-raydiffraction analysesat every 50 degreesfrom room ‘ It~II ~Itemperatureup to 1163 K werecarriedoutby usinga Y2-type X-ray diffractometer.X-ray diffractionscans(30 minutes)weretakenat eachtemperature. • .

3. Resultsanddiscussion 3u0~,J~

Fig. 1 showsthecurvesof the ac susceptibilityaswell as resistivityversustemperaturefor samplesAand B. The magneticmeasurementsindicate thatthereareat leasttwo superconductingphasesinsam- 1123Kple A. Onehasa T~of 110 K andtheotherbecomes

~I02~Ksuperconductingat 80 K. Eventhoughthe resistivityof sampleA hasa sharpdecreasenear115 K, it doesnotreachzerountil the temperatureis loweredto 88K. It is obviousthat the high-Taphasein sampleAis not sufficient to makea continuouspercolatingpath.In sampleB, the zero resistanceis achievedat104 K. Susceptibilitymeasurementsshowthat thereare at leasttwo superconductingtransitionsat 107

723Kand 102 K, respectively.Comparingthe X-ray dif-fraction patternsat 300 K in figs. 2 and3, it is ev- 623 Kident that there is more high-Ta phasein the Pb

containingsamplethan in the Pb-freecompound.Phaseanalysisby X-ray andelectrondiffraction

was performed. The X-ray diffraction patternsof50 40 30 20samplesA andBat 300 K aredisplayedin figs. 2 and 20,( )

3. Theresultsshowthat therearetwo face-centeredorthorhombicphasesandCuOin bothsamples.The Fig. 2. High-temperatureX-raydiffraction patternsofsampleA.

unit cell parametersfor the two orthorhombicphases Closedcircles, low-T,, phase;crosses,high-T, phase; triangles,CuO; opencircles,Sr

09Bi1 O2~5;squares,CaO.insampleAare:0.541(0)x0.542(0)x3.07(8)nmand 0.540(6)xO.543(0)X3.66(7) nm, which cor-respond to the low-T0 and high-Ta phases,respec- tively [7]. In sampleB, the cells of the 1ow-T~and

high-Ta phases are: 0.539(9)xO.545(7)x3.07(7)

50K 07K nm and 0.540(1)x0.545(4)x3.66(9) nm, respec-tively. Moreover, we have indexedthe X-ray dif-0

fraction lines of both superconductingphasesin—l samplesA andB. The resultsare given in tables 1“C

2 and2.102K—2 1.0 ~ The electrondiffraction patternsshownin fig. 4

B alsodemonstratethat therearetwo different phases8

8K~~t,J in sampleB. The unit cell parametersof the two_____________________ 0.0 ~

50 75 100 125 ISO phasesas determinedby the electrondiffraction,T. K shownodifferencefrom thoseobtainedby theX-ray

Fig. 1. Resistivityandacsusceptibilityof samplesA andB asa experiment.Fig. 5 is an SEM pictureof sampleB.functionof temperature. EDX analysisindicatesthat,besidethe two super-

442

Volume 133, number7,8 PHYSICSLETTERSA 28 November1988

~The indexedX-raydiffraction lines for Iow-T~andhigh-T,phasesin sampleA.

MIOK • ~ Low-Taphase High-T.phase I/Ia

17.973 00 2 17It 15.492 00 2 37 C

5.133 006 004 14

~ll43~J~ 3741 11 3 100 C

3.247 Il 5 453.076 0010 0012 95

6 0014 18

2.599 20 4 18300K ~ • 2.558 0012 58

A 2.030 0210 0018 262.008 1113 181.914 22 0 22 0 26

50 40 30 ~o 1.893 22 2 1117 151.857 0212 15

20,(’) 1.803 1115 23

Fig. 3. High-temperatureX-ray diffraction patternsof sampleB. 1.706 20 14 2 2 10 12The symbolshavethesamemeaningasin fig. 2. 1.631 1117 2 2 10 15

1.592 3 1 7 Il 21 151.541 0020 16

conductingphasesand CuO, thereis a minorphase 1.524 3 1 9 13with a compositionclose to (Sr06Ca04)Cu17503,which hasbeenpreviouslyreported [81. Thereareno PbOlines in theX-ray diffraction patternof sam- the peaksof the high-To phaseincreasewith tem-ple B, andno PbOinclusionswere foundby SEM- peratureandthat the optimum temperaturerangeEDX. TEM-EDX analysisof sampleB revealsthat for the formation of the high-Taphasein theBi—Sr—the chemical compositions are approximately Ca—Cu—Osystemis between623 and 773 K. FromBi4Pb1Sr4Ca3Cu6O,in the high-Tv phase and 823 to 923 K, the peaksof the high-Ta phasede-Bi4PbSr4Ca2Cu4O,,in the low-To phase,which in- creaseslowly andthis is accompaniedby anincreasedicatethat the ratios of Cu/Bi andCa/Bi are both in the diffraction from the CuObyproductandthehigherin the high-i’. phasethan thosein the low-Ta appearanceof some new phases,which we havephase.There is no doubt that Pb entersinto the identified asCaOandSr09Bi110255.Thelatteris te-structuresof the superconductingphases.Compar- tragonalwitha = 1.332(9)nmandc=0.425(7)nm.ing the unit cell parametersof the superconducting It is probablethat the high-Ta phasebegins to de-phasesfor the two samples,it can be seenthat Pb composeintoCaO,CuOandSr09Bi1102.55above823additiondoesnot changethec axis,but increasesthe K. From 1023 to 1123 K, the diffraction intensitiesratio b/a slightly for bothphases. of thesethreephasesdecreasewith increasingtern-

The high-temperatureX-ray diffraction patterns perature. CaO and Sr09Bi1 .102.55 disappearcom-for the Pb-freesampleA are presentedin fig. 2. It pletelyat 1123 K. It is believedthatCuO, CaOandcanbe seenthat from room temperatureto 773 K Sr09Bi11O255aretransformedinto the low-Ta phase

443

Volume 133. number7,8 PHYSICSLETTERSA 28 November1988

Table 2 oxygensothat theunknownhigh-temperaturephaseThe indexedX-raydiffraction lines for low-T, andhigh-T.phases mayhavea structurewithan oxygendeficiency.Thein sampe B. lost weight is partly regained by decreasing the tern-

DOb, Low-T,phase High-T,phase iji~ peraturefrom above1123 K to room temperature.(A) Only the diffraction from the low-Ta phasecan be

h k I h k I observedin theX-ray diffraction patternof thesam-

18.167 00 2 28 pIe which hasbeenannealedat 1163 K.15.278 0 0 2 26 Fig. 3 showsthe X-ray diffraction patternsof the5.029 0 0 6 17 Pb-containingsample from room temperatureto3.837 00 8 73 1163K. Thesepatternsrecordedattemperaturesbe-3.707 II 3 38 .

3.573 11 3 low 1123 K do not differ much. It is interestingto3.401 1 1 5 29 observethat the diffraction from the high-T. phase3.240 11 5 82 evenincreasesat 1143 K. It is obviousthat thehigh-3.074 00 10 00 12 100 T~phasein the Pb-containingsampleis a stableone2.8 78 11 ~ at hightemperature.We haveverified this by heating2.808 Il 9 452701 20 0 20 0 87 a Pb-containingsamplewith a T0 of 103 K at 111321652 2 0 2 45 K for 24 h followedby rapidcooling. It wasobserved2.616 00 14 26 that this samplehada T~0of 101 K. It canbe seen2.593 20 4 26 from fig. 3 that at a temperaturebetween1143 and2.5 60 0 0 12 79 1163 K thesuperconductingphasesaretransformed2.532 2 0 ~ into a new phase,which is similarto that foundin

2.018 20 10 41 sampleA at 1163 K. Whenthe sampleis cooledto2.006 1113 32 room temperaturefrom 1163 K, only the low-To1.9 19 22 0 39 phasecan be observedin the X-ray diffraction pat-1.908 22 2 54 tern. Exceptfor somedetailsabove1123 K, the TG1.891 2014 371 873 02 12 30 andDTA behaviorsof the samplesA andB are also1.803 1115 57 quite similar.1.631 1117 0218 391.621 2210 341.602 13 ‘~ 30 4. Conclusions1.595 11 21 291.589 13 9 371.580 3 1 9 30 (1) Pb canbe incorporatedinto the structureof1.553 2 0 16 2 2 14 27 the Bi—Sr--Ca—Cu—0superconductorsby a two-step1.535 1 3 9 42 sinteringprocess.Theadditiondoesnotsignificantly1.526 2 2 12 40 changethe unit cell parametersof the supercon-

ducting phaseswith the exceptionof increasingtheratio of b/a by aboutonepercent.

at that temperatureso that the diffraction from the (2) Thehigh-Taphasein theBi—Sr--Ca—Cu—0sys-1ow-T~phaseis much strongerthan that from the tern is not stableabove823 K, while that in thePb-high-Ta one. That is why the Bi—Sr-.Ca.-Cu—0su- substitutedBi—Sr—Ca—Cu—0 systemis stableup toperconductorpreparedby rapid cooling from the 1143K. The additionof Pb enhancesthe high-tern-temperaturesnear 1123 K is a single low-To phase peraturestabilityaswell astheproportionofthehigh-with T,~0 85 K. Thereis a phasetransformationoc- T~phase.curring above 1123 K. We havenot identified the (3) The optimum temperaturerange for forma-new high-temperaturephaseyet. The phasetrans- tion ofthehigh-Tophasein theBi—Sr—Ca—Cu—0sys-formationcanalso be seenfrom the TG andDTA tern is between623 and773 K.curvesshown in fig. 6. Theweight lossabove1123 (4) In the Pb-containingBi—Sr—Ca—Cu—Osuper-K on theTG curve maycorrespondto the releaseof conductors,thechemicalcompositionsoflow-Taand

444

00

a

000

000 000

a.Fig. 4. Electrondiffraction patternsof Iow-T, phase((a) and(c)) andhigh-1~phase((b) and (dl) in sampleB. The patternsof(a)and(b) arein the[001] orientation,whilethatof (c) and(d) arein the [130] orientation.

100 ~ 100�t-

___________ 96 ~I1iK 96

273 473 673 873 1073 1273Fig. 5. The SEM micrographshowing the different phasesin 1. Ksample B. (a)—(d) indicate the high-T. phase, CuO,(Sr

06Ca04)Cu17503,andthelow-T, phase,respectively. Fig.6. TG andDTA curvesof samplesA andB.

Volume 133, number7,8 PHYSICSLETTERSA 28 November1988

high-Tv phases are approximately: Bi4Pb1Sr4- [21 M.K. Wuetal.,Phys.Rev. Lett. 58 (1987)908.Ca,Cu40,and Bi4Pb1Sr4Ca3Cu6O~,respectively. [3] Z.X. Zhaoetal., KexueTongbao(1987)421.

[4] H. Maeda,Y. Tanaka,M. FukutomiandT. Asano,Japan.J.AppI. Phys.27 (1988)L209.

[5] C.W. Chu, J. Bechtold,L. Gao, P.H. Hor, Z.J. Huang,R.L.Acknowledgement Meng,Y.Y. Sun,Y.Q. WangandY.Y. Xue, preprint, Phys.

Rev.Lett.,to bepublished.

The authors would like to expresstheir apprecia- [61S.A.Sunshine,T. Siegrist,L.F. Schneemeyer,D.W. Murphy,tion to Mr. Guo-XunLi forhis help in carryingout Ri. Cava,B. Batlogg,R.B. vanDover, R.M. fleming, S.H.

Glarum, S. Nakabara, R. Farrow, J.J. Krajewski, S.M.the TG and DTA experiments. They also want to Zaburak,J.V. Waszczak,J.H.Marshall,P.Marsh,L.W. Ruppthank Mr. Pei-WenHua for the T~measurements, Jr.andW.F. Peck,Phys.Rev.B 38 (1988)893.

Ms. Xu Sunfor theXDA experimentsandMr. Feng- [7] H. Maeda,Y. Tanaka,M. Fukutomi,T. Asano,K. Togano,

ShanBu for his technicalassistance. H. Kumakura,M. Uehara,S. Ikeda,K. Ogawa,S. Horiuchi,Y. MatsuiandH. lchinose,preprint.

[8] R.M. Hazen,C.T. Prewitt, R.J. Angel, N.L. Ross, L.W.FingerandC.G. Hadidiacos,preprint.

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