Synthesis of Unidirectionally Solidified Y-Ba-Cu-0 Bulk Superconductors with High Critical Current Densities
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SYNTHESIS OF UNIDIRECTIONALLY SOLIDIFIED Y-Ba-Cu-O BULK SUPERCONDUCTORS WITH HIGH CRITICAL CURRENT DENSITIES E. YANAGISAWA, S. KONDOH, J. SHIMOYAMA, J. KASE, T. MATSUBARA AND T. MORIMOTO Research Center, Asahi Glass Co. Ltd., 1150 Hazawa, Kanagawa, Yokohama 221, Japan
ABSTRACT (Y,Ho)-Ba-Cu-O superconductors with the high critical current densities (Jc) in an applied magnetic field have been synthesized by a unidirectional melt solidification method. Melt solidified bulk materials are composed of large plate-shape (YHo)Ba 2 Cu3Oy crystals which contain small (-5 pm) particles of (Y,Ho) 2 BaCuO 5 . The Jc value of the melt solidified (Y,Ho)-Ba-Cu-O sample is 1I0000 A/cm2 at 77K, H = IT and this value is much higher than the value of 4200 A/cm2 of the melt solidified YBa-Cu-O sample.
INTRODUCTION Since the discovery of high-Tc superconductors [1-3], tremendous efforts have been made to apply these materials to practical uses such as wires for superconducting magnets. However, the Jc values of polycrystalline bulk materials are low because of weak coupling between superconducting regions at the grain boundaries. This effect reduces the Jc values especially in a magnetic field. Although it was reported that 2 the Jc value at 77K of Ag-sheathed Bi-Pb-Sr-Ca-Cu-0 wire was •17400 A/cm in zero magnetic field, the Jc value decreased-drastically by two orders of magnitude at H = IT [4]. Jin et al. applied the melting and solidification method (MTG-method) to the Y-Ba-Cu-O system in order to synthesize bulk materials with single crystal-like microstructure which suppresses the reduction of Jc in a magnetic field [5]. Murakami et al. applied the quench and melt growth technique (QMG-method) to the synthesis of Y-Ba-Cu-O specimens [6]. In this technique, a multiphase material was prepared by quenching a Y-Ba-Cu-O melt. This material was partially remelted and unidirectionally solidified. The microstructure of this specimen was single crystal-like as the sample of Jin et al., but the YBa 2 Cu3Oy crystals contained small Y2 BaCuO5 crystals. In addition, the Jc value of this specimen in a magnetic field was higher than that of Jin et al.[6]. In our previous study [7], we synthesized unidirectionally solidified Y-Ba-Cu-O bulk materials with single crystal-like microstructure by applying the
Mat. Res. Soc. Symp. Proc. Vol. 169. ©1990 Materials Research Society
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peritectic melting nature of YBa 2 Cu3Oy-Y 2BaCuO5 [8,9]. We determined the optimum initial mixing ratio of YBa 2 Cu3Oy and Y2 BaCuO5 powders as 7:3. 2 The maximum Jc values are 12000 A/cm2 and 4600 A/cm at 77K, H = 0.2T and The magnitude of the reduction of Jc in a magnetic IT, respectively. field is much smaller than that of the Bi-Pb-Sr-Ca-Cu-0 system mentioned In the present study, we investigated the effect of lanthanide above. atom doping in the unidirectionally solidified Y-Ba-Cu-O system on the Jc, microstructure and the remanent magnetization relaxation.
EXPERIMENTAL PROCEDURES
Powders of LnBa 2Cu3Oy and Ln 2BaCuO5 were synthesized by solid state reaction of
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