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MATERIALS RESEARCH

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Effect of sintering periods on the microstructure and electrical transport properties of high-Tc superconducting Bi–(Pb)–Sr–Ca–Cu–O tapes N. V. Vo, H. K. Liu, and S. X. Dou Center For Superconducting and Electronic Materials, University of Wollongong, Northfields Ave., Wollongong, New South Wales 2522, Australia (Received 16 May 1995; accepted 27 October 1995)

The effect of sintering periods for monocore (Bi, Pb)2 Sr2 Ca2 Cu3 O101x (Bi-2223) tapes on microstructure and critical current density sJc d have been studied. The results show that long sintering periods (of duration >100 h) give better grain growth, but greater misalignment. Prolonged sintering also necessitates the increase in porosity of the core due to random grain growth, increasing the chance of penetrating into the silver matrix and oxide core interface. Critical currents for long sintering periods are found to be lower in comparison with those obtained for slightly shorter sintering periods. The increase in frequency of intermediate cold uniaxial pressing between sintering periods assists grain alignment. However, when the sintering period is further reduced by increasing the frequency of intermediate deformation, it is found that microcracks are unable to heal as there is not enough time for grain regrowth. The tapes made using “three-to-four-sinter-period” (each period ,60 h) show superior electrical transport properties which are attributable to the fact that their oxide core is more dense and better aligned relative to the “two-sinter-period” (each period >100 h) tapes and contain less cracks relative to the “five-to-six-sinter-period” (each period ,40 h) tapes.

I. INTRODUCTION

Unlike Bi-2212 tapes, the fabrication of long length Bi-2223 high temperature superconducting (HTSC) tapes normally involve more than one sintering process, with an intermediate mechanical deformation step between each sintering period. This increases the chance of damaging the tape by accidental breakage of the superconducting core due to repeated processes. It is therefore desirable to determine the best least number of sintering periods in order to minimize the frequency of handling on these tapes. To achieve this, three differently processed precursor powders all having the same stoichiometric composition of Bi : Pb : Sr : Ca : Cu ­ 1.84 : 0.35 : 1.91 : 2.05 : 3.05 were used to fabricate monocore short tapes. This paper sets out to show the effect of different sintering periods on the microstructure and final electrical transport properties of high-Tc superconducting Bi–(Pb)–Sr–Ca –Cu– O tapes.

II. EXPERIMENTAL DETAILS

The monocore HTSC tapes were fabricated as follows. A silver tube of 99.99% Ag purity, one meter long having inner and outer diameters of 4.5 and 6.5 mm, respectively, was burnished, heated at about 600 ±C to eliminate organic contaminants, then cut into shorter sections of length 100 m. One of the ends from each J. Mater. Res., Vol. 11, No. 5, May 1996

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