Superconducting behaviour of Bi1.7Pb0.2Sb0.1Ca2.0Sr2.0Cu2.8Ox

~

S o l i d State Communications, V o l . 71, No. 11, pp. 935-938, 1989.

P r l n t e d in Great B r l t a l n .

0038-i098/8953.00+.00 Pergamon Press p l c

SUPERCONDUCTING BEHAVIOUR OF Bil.TPb0.2~0.1Ca2.0Sr2.0Cu2.80x P.V.P.S.S. Sastry, J.V. Yakhml and R.M. lyer

Chemistry Division, Bhabha Atomic Research Centre, Trombay, Bombay-400085, India (Received

June 8 t h , ]989

BI Pb Sb Ca Sr m~t~x 01~ac~f~n ~ t h ' ~

by

P. Wachter)

Cu

O samplas prepared by s~d~ xa sharp drop In electrical resistance between 145K and 124K after partial m e l t l ~ and annealing for 50 hours. 1"he dc magnetic susceptibility shows evidence of a bulk superconducting phase at T c = 109K but the R(T) curve does not show zero-resistance at this temperature and depicts a foot below 124K. The ol~erved superconductl~ behaviour is stable upon thermal cycling between 77K and 300K.

1,2 It is now established that Incorporation of Pb In BI-Ca-Sr-Cu-O system promotes the growth of the 110K-superconductlng phase BigCaoSr~Cu30 L0 (BI-2223) and improves tts buTk dbnt'ent. P; number of reports have appeared In literature which deal with the Influence of different parameters such as ca~tlon-nonstoichiometry,3 oxygen partial pressure" and heat-treatment conditions5 on the synthesis of BI(Pb)-Ca-Sr-Cu-O superconductors. Silver, when used as an additive Is shown to sharpen the superconducting 6 transition temperature In Bi(Pb)-Ca-Sr-Cu-O. Particularly lnteresti~g results have been reported by Hongbao et al ~ on the Influence of Incorporation of Sb in raising the Tc of BI(Pb)-Ca-Sr-Cu-O to above 150K. AC-susceptiblllty measurements by these authors on ( B i . _ xPb ~ 0 l)Ca2Sr"Cu^"/3 ~O (where x = d.'~- an~ 0.3) prgvid~'R "~vi~ence for superconducting phases with Tc values between 155K and 170K which deteriorate upon thermal cycling although the zero-resistance temperature in the Initial measurements was only between 110K and 117K, except for the sample Bi. 7Pb^ ^Sb^. Ca^Sr^Cu^ .O which showed a 11~=,0U ~ a t ~ ' l a t Zl6~K. z ~ e Y same authors In an earlier paper 8 reported large drops in AC-susceptibillty of B I . ^ x P h Sh0 .Ca^Sr-Cu.O (x = 0.3 and 0.4) at 1 ~ , e~en "alfte~ r~pe~te~ thermal cyclings. We have recently observed9a stable zero resistance state at 120K in BI 1 6Pb^ .Ca^Sr^Cu_O samples synthesized using a " prUd(~urs~r z ~a~rlx method. Detailed experimentation in our laboratories on BI- and Tl-based oxide superconductors have shown that, in general, the samples synthesized by a quick reaction of a precurssor matrix (say, Ca^Sr^Cu30 with BI_O_+ Pb-acetate) Rossess lml~ro~ed sYuperconduct~ngJ characteristics. 9-13 In this paper p we report the synthesis and superconducting characteristics of B t . . P b ^ ^Sb^ .Ca..Sr^Cu^-O which was prepared wiLh' t~I~ tUd~hnl~ue', z ~1~ ~natrix, Ca.Sr~Cu 2 80./ for this purpose was prepared by ~cho~ou~ly

mixing the appropriate amounts of CaCO3, SrCO. and CuO, and heating the mixture in an alumln~ boat at 1240K for 72 hours with several intermediate grlndlngs. Stoichlometric amounts of (matrix + BlgO3+Pl>-acetate+SbgOq) were mixed well, pelletls4~d and heated a f 1"200K In air f o r - , 5 - 1 0 minutes t i l l the mass turned black. The preduct was cooled, ground well, repelletlsed "and slnterecl at I I40K for 7 days with several Intermediate grlndings. "['his bulk sample was in the form of discs of 12 mm. dia and I0 ram. thickness, and Is hereafter referred to as sample @I. This sample, although metallic In nature, was not superconducting down to 77K. This behavlour is In sharp contrast to that of B i . . P b ^ .Ca-Sr^Cu.O , prepared using exactly

ldJa~ica~'4he;t-t~eati~J;t protocol as abo,e, which gave Tc(R=0) = 104K (sample A in reference 9). A portion of sample ~ 1 was ground and repressed Into thin pellets ( N 12ram. diameter x 2ram thick) and heated In air at I I 9 0 K for 3-5 minutes only, during which It became soft and warped visibly. At this point, these pollets were withdrawn from the furnace and annealed at I I40K for (i) 50 hours; (ii) 100 hours; and (iil) 150 hours, and furnace cooled. These samples are hereafter referred to as @2, ~ 3 , and4tt4, respectively. X-ray powder diffraction patterns were recorded with Nl-flltered C u - K ~ radiation on a Phillps PW 1050 wide angle goniometer. Electrical resistivity measurements were made using a standard DC four probe method with sample dimensions ~ l m m x l m m x l 0 m m In the temperature range 77K to 300K. Fine copper wires applle~! with sliver paint served as electrical leads and constant DC currents of 1 or 10 mA were passed through the sample during measurements. The voltage across the sample was measured using a Datron Autocal multimeter medel 1 0 7 1 with a resolution of 0.1 ~ V. Temperature was measured with calibrated copper-constantan thermocouple and the error 935

936 in

SUPERCONDUCTING BEHAVIO~ OF Bi i.7Pb0.2Sb0. iCa2.0Sr2.0Cu2.80x measurement of

temperature did not exceed

+_0.5K. Flg. I shows the reslstlvity behaviour as a function of temperature for samples ~2, # 3 and ~ 4 . A sharp drop In resistance was observed for s a m p l e ~ 2 from 145K upto ,-.124K. However, the resistance did not fall to zero upon cooling even down to 77K, and a foot appeared In the resistivity plot after which the resistance dropped

again

upon

cooling to

a

R(77K)/R(300K) = 0.02, existence of a second

rather

low

value,

Indicating the possible superconducting phase.

This is a case similar to the observations of two superc.~)nductlng phases by Maeda et al for BI-I112.14 The magnitudes of the sharp R-drop between '145K and 124K, however, reduced substantially" upon additional 50 hr~

heat-treatment, as seen

for sample ~ 3 in Fig. I, although the shape of the resistivity plot remained essentially similar. Further heat treatment of 50 hrs ( # 4 ) gave rise to a semlconducting behavlour between 220K and 145K before a drop in resistance occurred upon cooling the sample upto 120K. But the fractional resistance for sample ~:4 is high i.e` 1.2

I.O ,, ...,.. ,. ,, ...."~"""'""'"'"'"

0.8 v O O IO

~O.6

0.4

Vol. 71, No. 1i

Indicating a substantial deterioration of the sample, These observations are in sharp contrast to our result for BI .Pb 0 .Ca2Sr^Cu.O which continued to yield a IRP=0 ~ a t e a~ 1~01~ (curve C In fig.l) despite successive heat treatment of upto 170 Hours at II40K. In fact, Identical results (R-0 at 120K) have been obtained for the sample B I - . P b ^ - C a ^ S r ^ C u . O too, under heat-treatment pr~t~co~'~de~tl~ai ~oYthat for sample # 4 above. Our results therefore Indicate that Sb-doplng In BI(Pb)--Ca-Sr-Cu-O does not lead to any Improvement in superconducting characteristics. On the contrary, BI 1 7Pbn oSbn ICa~SroCu9 R O displays merely a sharp " R - d ~ Ir~'tthe"tefflpef~[fur~ range 145K-124K, which extrapolates to an R=0 state of NIIOK, although it Is not reallsed in practice. The existence of such a superconducting phase (Tc ~ I IOK) Is proved from the dc-susceptlbillty data (Fig. 2) showing a sharp diamagnetic onset at 108.51~ The volume fraction of this superconducting phase has been estimated to be 31%. Despite this, the sample not exhibiting a zero resistance at ~ I I O K is quite Intriguing, and points to a lack of connectivity between the grains containing this phase. It is likely that the hlgher-Tc phase(Tc~ I IOK) in our samples Is located in the core of the grains, the shell of which may be comprising the lower-Tc phase. One could then obtain a foot In the resistivity curve. An Identical situation has been observed for the j'~sistlvlty behaviour of BI.Ca.Sr.Cu~O samples~V where a sharp drop w~as 4obtained Ybetween I ISK and 105K, but a foot In resistivity curve appeared upon further cooling and resistance became zero at 80K only. Our own Bi~CaASrACURO" samples, prepared using the matrlx-reaEtidn fne~hod, gave improved superconducting behaviour to the extent that the drop In resistance was sharper (,~80%) and It shifted to higher temperatures i.e, between 122K and II4K (Curve D in Fig.l). But the foot In resistivity curve remained and an R-0 state was obtained at 80K only. XRD patterns for "samples ~ 2, ~ 4 and Sb-free sample BII~Pb^ .Ca..Sr^Cu~O (Tc = 120K) are given in ~'~ig.Vj~. A~I ~be~e Ysamples contain lines due to-151~2223 phase as well as BI-2122. BI-2223 phase appears to be reasonably well-developed R(77K)/R(300K) ~ 0.72

#3/"/ i

,

BIl. 7 Pbo.2 Sbo.l C ° 2 . 0 Sr2.0 C u 2 . 8 0 x

C

0.2

.....jo/ 0.0

I

0

50

/,--5" I00

Fig. 1. Normalized versus

t 1

150 T (K)

,

,

200

250

resistance,

temperature(K)

sample

R(T)IR(300K) plots for

Bl5Ca4Sr4Cu8Oy : sample D.

C,

. s e ~'

300

BI 1.7Pb0.2Sb0. I Ca2.0Sr2.0Cu2.gOx samples ~I~2, ~t3 and 4t4; Bil.6Pb0. 4Ca2Sr2Cu3Oy:

O-

and

• ,e• 80

I 90

./ I I00 "r(K)

I I10

Fig.2. dc magnetic susceptibility vs. temperature (K) for Bll.7Pb0.2Sb0.1Ca2.0Sr2.0Cu2.80x (Sample ~2).

120

Vol. 71, No. 11

SUPERCONDUCTING BEPAVIOUR OF Bil.7Pbo.2Sb0.1Ca2.0Sr2.0Cu2.80x X I

(C)

Indicating the adverse effect of prolonged heating on ~ 4 . There was a need to assess, therefore, whether any preferential loss of Sb or Pb has occurred in sample ~/t4. A chemical analysis conducted on this sample showed that none of these elements has been lost significantly. All these results point to the conclusion that Pb-lncorporatlon In BI--Ca-Sr-Cu-O does help In raising the R~0 state to higher temperatures 9bY actually removing the foot In the c u r v e . On the contrary, Incorporation of Sb In BI(Pb)-Ca-Sr--Cu-O system does not appear to have any beneficial effect and only leads to the reappearance of a foot In the R(T) curve. It Is likely that the higher-~'~ Phase ( ~ 130K) reported by Hongbao et al ' ' v is a transient phase of filamentary nature, which possibly gets killed by passing substantial currents (say, : ~ 5 ) ~ . ~ or by thermal cycling. Chert Zuyao et al 6 too, have found a pronounced dependence of the resistive transitions on measuring current in BI(Pb,Sb)-Ca-Sr-Cu-O samples. For Instance the Tc (R=0) for Bl_--Pb- _Sb_ .Sr2Ca^Cu^O was 130K, l lBK and ~b~ ~ e n U ' ~ e m~asu~ln~ current was IO~A, IOOjM.A and lmA. 7&n Important observation made by Hongbao et al was that the very high Tc (Rffi0 at 164K) state in (Bl I ^ PbxSb0 I) Ca^Sr^Cu 2 ^O sample was stable "~l~y If "t~e ~ m ~ l e "~a~( cycled between 77K and 200K, and, it, quickly deteriorated to 122K (R=0) when the sample was cycled to room temperature. Other samples, too, showed a marked dependence upon thermal cycling. The Initial R=0 state at 132K for Bi. 9 xPhxSh0 .Ca.Sr^Cu-O (x=0.3 amd 0.4) c a h E down t~ fi21~ (~ ~3) and 106K (x=0.4) upon cycling between 77K and room-temperature . However, in the case of R(T) data reported in Fig. 1 by us for B I - P b ^Sb0 .Ca^Sr^Cu^ ^ O , all measurements we~ ~e ~de~ r ~ e a ~ l n ~ currents of lOmA and the resistance behavlour of 4~2, @ 3 and ~4 was stable upon thermal cycling between 77K and 300K.

I

Z )rr

~4

t~

m e~

,

X

I.z w p. z H

x

,/~2

x

I

30 2e (DEGREES)

40 Fig.3. X-ray at ~4

room

diffraction

patterns

temperature

for

937

20 recorded sample # 2 ,

and C. Lines marked with X belong

to BI-2223 phase. l n ~ 2 and In BII.6Pb^ 4Ca2Sr^Cu30 , but the XRD peaks corresl~ndl~]~ to t~ts phase become we~ak in ~ 4 . In particular, the peak at 2 0 = 24~ (hkl = 1 0 3 ) has completely disappeared

A very recent paper by Dou et a117 essentially supports our conclusion that the doping of Sb in BI(Pb)-Ca-Sr-Cu-O depresses Tc(R=0) apart from stabllising another weak superconducting phase (T = 108K) which shows up only as a sharp dro~ In electrical resistance.

Acknowledgements The authors are thankful to Prof. R. Srinlvasan of I.LT., Madras for providing the magnetic susceptibility data presented in Figure 2.

References l. 2. 3. 4.

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SUPERCONDUCTING BEHAVIOUR OF Bi I .7Pb0.2Sb0. |Ca2.0Sr2.0Cu2.8Ox

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L209(1988). 15. T. KaJitani, M. Hirabayashl, M. Kikuchi, K. Kusaba, Y. Syono, N. Kobayashi, H. Iwasaki and Y. Muto, Jap. J. Appi. Phys. L1453(1988). 16. Z. Chen, W. Zhang, X. Mao, L. Zhou, Z. Mao, Qulan, L Can, Z. Chen and Y. Shang, Submitted to BeiJing Inst. Workshop on Hlgh-Tc Supercond., Sept. 4-8, 1989, Preprint. 17. S.X. Dou, H.K. Llu, N.X. Tan, Y.J. Sheng and W.K. Jones, Physica C 158, 97(1989).