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SUPERCONDUCTIVITY OF Bi 1 . 6 Pbo. 4 Sr 2 Ca2 (Cul.xAgx) 3 0y AND Bi 1 .6Pb

0

.4Sr

2 Ca2 Cu30y

+ wt% Ag

CHONGDE VEI, CHIN LIN. QINGRONG FENG, ZUNXIAO LIU, JIAN LAN, YUNXI SUN, GUOZHONG LI, KE VU. LIXIN XUE. ZIZHAO GAN Department of Physics, Peking University, Beijing, China ABSTRACT Both

interstitially Ag-doped Bi 1 . 6 Pb0 . 4 Sr 2 Ca2 Cu3 Oy÷ x(wtZ)

Ag

0.5, 1.0, 5.0, 10.0, 15.0, and substitutionally Bi 1 .6Pb. 4Sr 2 Ca2 (Cu with x = 0.025, 0.05, 0.10, 0.20, 0.40 1 -x Agx)0y

with x doped systems

were studied. Magnetic susceptibility measurements indicate that both the interstitial and substitutional Ag-doping yield much higher diamagnetic signal for ZFC in a field of 60 Oe at 5 K. At 80 K, -47CH/H was also enhanced by Ag-doping for H(200 Oe. Substitutionally Ag-doping also enhances the magnetic critical current for x e 0.2. Possible explanation vas discussed. INTRODUCTION Since superconductivity with onset temperature 100 K in BiSrCaCuO system was discovered[l], it was one of the most challenging task to single out the 110 K phase. Among the efforts it has been reported that partial substitution of Pb for Bi increases the superconducting volume fraction of the 110 K phase. We have measured the magnetic properties of Bi 1 .6Pb 0 .4Sr 2 Ca2 Cu3 0y [2]. The hysteresis observed in the magnetization versus field curve is much smaller in this compound than that in YBa 2 Cu3 07 -6 at high temperature. Lue at al have investigated the effect of Ag-doping

on

the

critical

current

density

of

YBa 2 Cu3 07 -6

superconductor[3], indicating that the interstitial Ag-doping yields higher diamagnetic signal and enhances the critical current. In this paper we report the effects of Ag-doping on the superconducting properties of Bi 1 . 6 Pb0 .4Sr 2Ca2 Cu3Oy. EXPERIMENTAL In this experiment, both interstitial and substitutional doping samples were prepared by solid state reaction. The composition and other parameters are listed in table 1. Magnetic measurements were carried out on a noncommercial magnetometer, which was made by Neel Laboratory, CNRS, France, and a vibrating sample magnetometer of model 9500, LDJ, with a sensitivity of 2*10-5 emu. Samples of No.1 to No.9 have the structure of 2223 phase and are essentially single phase. Samples of No.10 and No.11 are mixture of 2223 phase and 2212 phase. These results indicate that the addition of Ag to the Bi 1 .6Pb 0 .4Sr 2 Ca2 (Cu1 x Ag x) 3 0y is unfavorable to the formation of

Mat. Res. Soc. Symp. Proc. Vol. 169. ©1990 Materials Research Society

1090

J?23 ghase for x:- 0.2. isSEMinhomogeneous. semi-quantitative analysis withn atomsthat..tbe fInd Agshows We can istri ution of Ag atoms but the Ag content is different at grains and in the grain boundaries, different plase. The screening (ZFC) and exclusion of magnetic flux (FC) were measured in a field H of 60 Oe from T=1.5 K to 120 K. Fig. 1 is the M-T curves of It shows that the interstitial Ag-doping yields sample 1 and sample 4. rather larger diamagnetic signal. The superconducting volume fraction was i.e. -47