Das, B

Srivastava, O N

Verma, G D

IACS Institutional Repository

d,«„y.P/'y^ ’^ «A(l).95-99 (2002)U P  Aan iniernational journalSynthesis and microstnictural characteristics of Tl-based high temperaturesuperconducting tapesB Das\ G D Verma^** and O N Srivasiava^*' Department of Solid Stale Physics and Electronics. Dr R M L Avadh University, Faizabad-224 001, Uttar Pradesh, India - School of Pure and Applied Physics. Guru Ghasidas University,Biliispur-495 009, Madhya Pradesh, India’ Dcparlmcnt of Physics, Banaras Hindu University. Varanasi-221 005, Uttar Pradesh, India E-mnil ■ ons^hanarns.crnct indistract The superconducting tapes of Tl-Ba-Cu-Cu-O HTSC system were synthesised through doctor blade tape casting process Their KuLiurul-inicrostruclural characteristics were explored through X-ray diffraction (XRD) and transmission electron microscopic (TEM) techniques. A ivei leaiurc ol the present synthesis route was that here in the same ihallialion process, tapes of two different HTSC phases possessing single and Tl-0 layers / e TIBa^CnCu.O, (1212) and Tl,Ba,CaCu,0^ (2212) or TIBa,Ca,Cu,0,^ (1223) and Tl,Ba,Cn,Cu,Oj„ (2223), could be synthesised he iinnsition temperatures (T \)  of the us synthesised tapes were found in the range of -  80 -  I15KU‘>Mfirds Tl-based H T S C  tapes, synthesis, inicro-slruciural characteristics•ACS Nos. 74 72 Fq, 85 25 .KxI. Introductioniince the discovery of supcrconduclivity at -  35K in the La-Ba- Tli-O sy,<iem by Bednorz and Muller [1], many other cuprate Lipciconductors such as Y-Ba-Cu-0, Bt-Sr-Ca-Cu-0, Tl-Ba-Ca- u () and Hg-Ba-Ca-Cu-012-5] with superconducting transition cmpciatures (T.^ y) above liquid nitrogen temperature, have been liscovcred. However, practical applications of these materials lave been hampered by two major difficulties : the low critical urrcnl density (7^  ) and the poor mechanical properties. These wo problems are indirectly associated with the granular nature »l ihese materials. The first requirement for large scale ipplications of these HTSC materials is that the materials be ivailablc in polycrystalline form which is not eleclromagnetically granular. Unfortunately, all the high 7  cuprate superconductors, 'xccpi Bi-based, are clectromagnelically granular in all fields. Hlowcver, Tl-based superconductors with monolayer of Tl-0 appear to have high current carrying capacity in high magnetic Ticlds due to comparatively closely spaced CuOj layers in these materials [6,7]. Thallium is also known to passivate the grain boundary and hence increases the intergrain critical current (7 ).^»rtcspond ing  A u th o r Prcsuiii a d d re s s  Departm ent of Roorkce-247 667 (U. A.), India.Physics. NT Roorkee,Another problem concerning with the brittleness of HTSC materials, can he overcome by fabricating mctal/superconductor composites, such as mctal-clad wires, tapes and multifilaments [8, 9]. Furthermore, the metal {e,g. silver) provides a means of thermal dissipation, thus stabilising the superconductor's environment.The doctor blade process (DBF) [lO], among the various methods to produce mctal/superconductor composites, has proved to be an attractive route for producing very long homogeneous superconducting lapcs/wires. However, despite the known facts regarding the superiorities of thallium based cuprate superconductors e.g. the occurrence of higher T^s in this system (7^  -  127K for T1:2223 phase [II]) and the fact that excess T1 can passivate the grain boundaries and thus minimise weak link effects, rather sparse studies have been made in the case of Tl-Ba-Ca-Cu-0 tapes/wires. Only some studies on T1 bearing cuprate HTSC tapes, employing the powder in tube (PIT) method, have been done so far [ 12-14], However, synthesis and formation of T l : HTSC tapes through the other well known technique -  the doctor blade process does not seem to have been carried out so far.Keeping these facts in view, we have employed the doctor blade pr(x:css for synthesis of Tl-bearing HTSC tapes in the©2002 lACS96 /i Das, G D Vernut and O N Srivastavaprcsenl investigations. Wc have also explored their superconducting and structural/ microstruclural characteristics. A novel feature of the present synthesis method relates to the fact thal here in the same lhallialion process, tapes of two different HTSC phases possessing single and double TI-0 layers1. e. TlBa^CaCu^O^ and TI^Ba^CaCu^O^ or TlBa^Ca^Cu^O^ and TI^Ba^Ca^Cu^Oj^j. could be .synthesised2. Experimental methodsIn the present investigation, the Tl-based cuprate tapes have been prepared by following a Ihrcc-slcps process. The salient features of this are described below.First of all, precursor oxide powder of nominal compositions Ba2CaCu2 0  ^and Ba^Ca^Cu^O, have been prepared by standard ceramic methfxJ [ 15,16]. In the second step, the slip was prepared by mixing thoroughly the precursor powder with fish oil and then stirring with an organic formulation consisting of a solvent (ethyl alcohol and trichloroethylene), binder (polyvinyl butyral) and plasticizer (polyethylene glycol + octyllhalatc). The resulting viscous fluid was finally cast under a doctor blade onto the carrier sheet (cellulose film), producing a green tape of 1 .(X) cm wide.The typical thickness of the as cast tape was about 2CK) pm. Small precursor tape (Ba-Ca-Cu-O) ol 10 mm long and 5 mm wide cut Irom the green tape was slowly heated (2‘’C/mm.) to 5(K)‘'C for 3h. and then cooled slowly (2'‘CVmin.) to remove the organic compounds from the precursor tape and to avoid the crack fonnation inside the tapes. Finally in the 3rd step, the dried precursor (Ba-Ca-Cu-O) tapes were lhalliated under TI^O  ^vapour m the two different configurations which are dc.scribed below.2./ Configuration-1 :In this configuration, appropriate amount of Tl.,0^ powder was taken in a platinum box and a precursor tape labeled as A oi A' (A / A') was kept above (- 2 mm) the Tl-,0^ powder asPrecursortapesB ^ C s Ba  ^Ca Cu^B C = Ba, Ca, Cu, 0 . Figure 1. Configurations of ihalhation of precursor (apes.shown in Figure 1(a). Here the precursor tape labeled  ^corresponded to com position Ba^CaCujO^ and A' (,, Ba^Ca^Cu^O^. The closed platinum box containing precursor tape was transferred into a silica tube attached wnf an oxygen flowing system. Finally, it was kept in a prehcincj programmable Heracus furnace at 9(X) ± I "C for about 12-15 inm in the flowing oxygen and allowed to cool at the rale of 2 T  mm uplo room temperature.2.2 Configuration-2 :In this configuration, two precursor tapes either B and C or  ^and C' were kept above the TI^O, powder as shown in Figun 1(b). Here, the precursor tapes H and C correspond i composition Ba,CaCu^O^; on the other hand B' and C' Ba.Ca.Cu^O^. fiic tapes B or B' i.e. (B /B ' ) were just abmi the TIjO, (- 2 mm) and C or C' {C/ C' ) above the tape /I//) as shown in Figure Kb). The closed platinum box coniainin;, 31,0^ and precursor tapes with above mentioned cgnfiguraiioi was kept inside the silica lube for thermal treatment , (riie Iheinia treatment was similar to configuration-1. \The gross phase identification of the as synlhesKcd HIS( tapes was carried out with a Philips PW-1710 diffi a^ctomcie having a wide angle goniometer filled with a graplm monochromator employing Cu-Ka radiation. The varialioii i resistance wilh temperature o\ the tapes was measured h slandard four probe method employing Ihe van der P.iii. technique. The current was supplied from a computer conlmllLi Kcilheley programmable constant current source (ModcF?'(i and the voltage was measured by a Kcilheley nanovoltniLii (Model-181). The sample was cooled by using a APD close cycle chiller.Since X-ray diffraction (XRD) reveals only the gros structures of the materials, the necessity of cairying out eicciio microscopic investigation for uncovering the strucliir;i microslructural characteristics at the microlcvel (nanoinciii dimensions) is evident. In order to achieve this goal. computeri.sed Philips electron micro.scope (EM CM-12) was um: in imaging and diffraction modes.3. Results and discussionAfter the lhalliation of the precursor tapes under tl configurations mentioned earlier, the lhalliated tapes we subjected to X-ray diffraction study for gross struciur characterisation and identification of HTSC phases present the as lhalliated tapes. The X-ray diffraction patterns ol tl lhalliated tapes A and A' are shown in Figure 2(a) and ( respectively. The analysis of the XRD peaks corresponding tape A [Figure 2(a)] revealed the presence of phase havii bodycentred tetragonal lattice structure wilh a = fc = 3.86 A ai c = 29.31 A. On the other hand analysis of XRD pea corresponding to tapes A' [Figure 2(b)] revealed the presen of phase having body-centred tetragonal lattice structure wi a = /? = 3.86Aandc = 35.95A.Synthesis and niicrostructural characteristics of Tl-based high temperature etc 97These results suggest that the thalliation of the tape A / A' j to the formation of double T I-0  layers compoundfor double TI-0 layers (2212, 2223) HTSC tapes at 77 K and zero field. It was noticed that T of the tapes B/B^ (which wereFigure 2. X-ray diffraclioii patterns of (a) the thniliaied tape A showing the presence of dominantly TI,BQ2^aCu,C)^ HTSC phase and (b) the lhalliatcd tape A revealing the presence of dominantly TI,Ba,Ca,Cu,0,„ HTSC phase (* represents impurhy phases.),Bi^CaCu20jj /TIjBa^CajCu^Ojjj. Similarly based on the XRD su its , It was found that thalliation of the tape B IB '  which ltc just above (- 2mm) thatTKO^ powder [Figure l(b)|, led toclose to the TIjO^ powder at a distance of ~ 2mm) was higher than the tapes QIC' (which were some what away from Tl20^ powder).10 16 22 2B 34 40 46 52 58 6426 (degree)Figure 3. X-ray diffraction paltcms of (a) the lhalliatcd tape C revealing the presence of TIBa,CaCUjO, HTSC phase and (b) the lhalliatcd tape C , showing the presence of dominantly TIBa^Ca,Cii,6y HTSC phase. (* represents impurity pha.scs)ic (( r^malton of double TI-0 layers compounds (T1; 2212/2223). he XRD patterns of the thalliatcd tapes C and C' have been lown in Figure 3(a) and (b) respectively. The analysis of these itierns revealed that thalliation of the tape Cled to the formation I TIBa^CaCu^O  ^(a = fc = 3.85 A, r = 12.75 A) HTSC phase and uiiol C  toTIBa2Ca2Cu3 0 9 (fl = /? = 3.85 A an d r=  15.85 A).FromR - T monitoring, the transition temperatures (T ’.v) of tc as synthesised tapes were found to be in the range of 80 -  15 K. The R -T curves corresponding to Tl- bearing HTSC tapes tbelcd as A and A' have been shown in Figure 4. The T . (R = >)tortapei4 w a s - 102 K [Figure 4(a)] and for tape A' - I lO K  igurc 4(b)]. Similarly T^s (R = 0) for thalliatcd tapes B and B' 1‘fiespnnded to -  99 K and 107 K respectively; and for thalliatcd 1^^ "'' C and C' -  87 K and 105 K respectively.Transport critical current density (J^) was also measured forIts synthesised tapes following the criterion of I |xV/cm. The ypical values of y '^s for the as synthesised tapes were -7 x 1 0 ^  for monoTl-O layer (1212, 1223) and -  4 x 10  ^A/cm^Figure 4. Resistance v.v temperature curves of (a) the thalliated tape A and (b) the thalliatcd tape A '98 B Das, G D Verma ami O N SrivastavaTTic microstruclural characlenstics of the as lhallialed tapes under configurations I and 2 as described in Sections 2.1 and 2.2 were studied by a transmission electron microscope using its various modes such as imaging, selected aiea diffraction (SAD) and convergent beam electron diffraction (CBBD). Figure .S(a) shows a representative selected area election diflraction pattern bringing out reciprocal lattice net taken from the sample ol the ihalliated tape labekd as A I he analysis of ther i^ i in -  s. (,|) | |n i ( ) |  S \ | j  | \ i i iu n  i>l i Ik- ih.dli.iii-d  l;ipc A, ihclelraponul phase w iih  a -  t A aiul t - W) A eoiiesponding lo 2212  phase and (b) H K R M  ol Ihe lha llia led  lape A depieling ik>I |)lane.s the  Irin jie speeing ol 2 ‘  ^ 10 A eoiiesponds lo ( p e iio d iu ly  o f 2212  phasepattern revealed the presence ol tetragonal phase with o = 3.S6A and c = 29,30 A. The c-periodicity of 29 30 A was also subsiantialcd by the presence of lattice fringes of spacing 29.30 A in the high re.solution election micrograph [Figure 5(b)J depicting or;/planes taken from the specimen of the tape labeled as A These kiltice paianieleis ( (Mrespnnd in Tl ■3212 phaseF ig u re  6. HREM of Tl hearing IITSC tape cxhibiiing the presence of stacking faults The width of the fault is -  20 AThese findings arc in conformity with the X-ray diffraction results. Similarly, TEM explorations of the samples of thalliaied tapes A \ BIB' and C/C' revealed the same structural features as obtained through XRD investigations. The TEM explorations also revealed the presence of stacking faults in the as synthesised tapes. Figure 6 represents the illustrative exainpk of the observed stacking faults (marked by arrows). It may be noted that the typical width of stacking faults is around 20 k This is compatible with coherence length; therefore, these stacking faults may serve as llux- pinning centres.The above studies revealed that tapes of both single I'l () as well as double I ’l-O layers compounds could be synthesised through the precursor tapes suitably exposed, in a single thallialion process. Both single Tl-O layer and double TI-0 layers compounds have their own merits in regard to their application potentiality. The double TTO layers compounds generally show higher 7’ as compaicd lo their corresponding (having same number ol CiiO^ layers) single TFO layer compounds. One mam advantage ol the double layers HTSC system such as B i: 2212 and 2223 is that the double layers ol HTSC phases correspond to van dcr Wall plaicicl like solid, where we have aligned and eleciromagnelically connected gram morphology leading to high grain lo gram J value On the other hand, singin Tl-0 layei compounds appeal tt; have higher current carryingyapacily m high magnetic fields due to comparatively closely spW'cd C uO, layers m lhc.se materials. ^4. ConclusionsIn ihe present invesiigations we have successfully synthesised the tapes of HTSC phases of TTBa-Ca-Cu O system llmuigh doctor blade process and the synthesis was so tailored ilrni based (m the same thallialion process, both the double and single Tl-O bearing HTSC phases corresponding lo either 2212 and 1212 or 2223 and 1223 could be synthesised. The R -1 monitoring of the tapes ihalliated under different configurations showed T \  in the range of 80 -1 I5K. The rcprcscnlatiu liansporl critical current density for the tapes synthesised m the present investigation was ~ 7 x lO*^ A/cnr for mono TI-O layer (1212 and 1223) and ~ 4 x 10** A/cnr for double TI-0 layci s (2212 and 2223) HTSC tapes Based on both the XRD and TFM studies it has been found that the lhalliation of the prccursoi tapes labeled as A/A 'and B/B which were in close proximity ol the TUO^ powder (at a height of ~ 2 mm) lead lo the formation ol double Tl-O layer compound of Tl-Da-Ca-Cu-0 system, namely Tl;2212 and 2223. On the other hand, the thallialion of the lapt^  labeled as C/C'which were some what farther (at a height of -4 mm) Irom TI^O  ^powder leads to the formation of single TTO layer compounds of Tl-Ba-Ca-Cu-O HTSC system, namely Tl 12l2and 1223.AcknowledgmentsThe authors arc grateful lo Prof. A. R. Verma. Prof. R. P. Rasiogi and Prof Yash Pal for encouragement. Extensive discussions with Prof, V. G. Bhide, Dr. A. V Narlikar, Prof. T  V. Ramakrishnan,Synthesis and microstructural characteristics of TUbased hi^h temperature etc 99prof. R, K, Singh and Dr. B. A. D asannacharya are gratefully acknowledged. The present w ork was financially  supported by ihc University Grants Com m ission and N.S.T.B. (the Department of Science & Technology).Kefercnccs11 1  J G Bednonr. and K A Muller Z Phys B64 188 (1986)12] M K Wu. J R Ashuburn, C J Tomg, P H Hor, R L Mciig, L Gao, Z J Huang, Y Q Wang and C W Chu PIm Rev. Uti. 58 908 (1987)13 ] H Macda. Y Tanaka. M Kukulomi and A Asano Jpn J AppI Phys 27 209 (1988)[4 ] Z Z Sheng and A M Hermann Nature 332 138 (1988)[31 S N Pulilin, E V Antipov, 0  Chmaisscn and M Marc^io Natiue 362 226 (1993)pi I D H Kim, K E Gray, R T Kainpwirih, J C Smith. D S Richeson, T J Mark, J H Kang, J TalvacLhic and M Eddy Phy\ira C 177 4^1 (1991)[7] R S Liu, D N Zheng. L W Lorain, K A Mirza, A M Cambell and P P Edwards Supercomiuctinff Ne\%s 6 Jan. I (1992)[8] T Hikala, T Nichikuwa, H Mukai, K Sato and Hiotsuyaiiayi J Appi Phys 28 288 (1989)19] S X Dou, H K Liu, J Wang, M H Appcrcly, C C Sorrell, S J Guo, B l.obcrg and K E Easterling Physua C 172 63 (1990)[lOJ K Togano, H Kuinakuru, H Macda, E Yanagi.sawa, N Irisawa, Shornoynwa and T Morimoio ,/pn J Appi. Phys. 28 L95 (1990)H 11 T Kaneko, H Yamauchi and S Tanaka Phy.sica C 178 377 (1991)fl2 ] B A Glowncki and S P Ashworth Plmico C 200 140 (1992)113] J G Hu, n  J Miller, K ( ' Gorella and R B Pocppcl IEEE Tron.sactarns an Applied Superionductivity 3 121.S (1993)II4J P J Kung, P G Wahlbcck. M E McHenry, M P Maley and D E Peierson Physira C 220 310 (1994)I l!ij IK  Gopulaknshnan, PVPSS Sastry, K Gangadharan, G M Phntak, J V Yakhmi and R M Iyer Appi Phys Lett 53 414 (1988)116J C D  Vcrina, K Ramaknshna and () N Snvasiava Ph\suu C 202 327 (1992)

Synthesis and Microstructural Characteristics of Tl-based High Temperature Superconducting Tapes

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Synthesis and Microstructural Characteristics of Tl-based High Temperature Superconducting Tapes

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