Fabrication of NdBCO single crystal oxide superconductor with enhanced superconductive properties
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Fabrication of NdBCO single crystal oxide superconductor with enhanced superconductive properties M. Kambara Department of Metallurgy, Graduate School of Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113, Japan
X. Yao, M. Nakamura, and Y. Shiohara Superconductivity Research Laboratory, ISTEC, 1-10-13 Shinonome, Koto-ku, Tokyo 135, Japan
T. Umeda Department of Metallurgy, Graduate School of Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113, Japan (Received 17 April 1997; accepted 22 July 1997)
Nd1+x Ba2–x Cu3 O6+d (Nd123) single crystals have been successfully grown by the top-seeded solution-growth method. Compositions of Nd123 could be controlled by applying two different methods: control of the oxygen partial pressure of the atmosphere and control of the liquid composition in air. The critical temperatures of Nd123 obtained by these two methods were 96 K (oxygen control) and 95 K (liquid composition control), respectively. The relationship between the peak effect in the Jc -H curve and heat treatment was investigated. The peak effect was found not to be an intrinsic property of Nd123; consequently it could be controlled by heat treatment.
I. INTRODUCTION
Since the discovery of RE1 Ba2 Cu3 O6+d [RE123 (RE: La, Nd, Sm, . . . )] oxide superconductors, much research has been carried out from both the fundamental and application points of view. RE123 superconductors have been expected to be applied to many kinds of future devices, as they have high superconducting transition temperatures sTc d. However, the RE123 superconductors containing light rare earths are solid solutions of RE1+x Ba2–x Cu3 O6+d and show relatively low Tc values because the RE ions easily substitute into Ba sites1–3 though no significant Ba site substitution occurs for RE’s heavier than Gd. Furthermore, it has been reported that they are no longer superconducting materials when the substitution ratio, x, is more than about 0.5.4–6 Therefore, it is essential to control and minimize the substitution ratio to synthesize RE123 superconductors with high Tc values (.90 K) and sharp superconductive transitions sDT d in dc magnetization measurements. Recently, Nd123 and Sm123 samples prepared by the oxygen-controlled melt-growth (OCMG) method were reported to have higher Tc values (96 K) and higher critical current density sJc d, especially under high magnetic fields, than those of melt processed Y123, due to the existence of the anomalous peak effect in the Jc -H curve.7–9 It was suggested that higher Tc values were due to the depression of the substitution, and the larger Jc in high magnetic fields was attributed to a slight chemical variation which was related to the substitution.7 However, only a few ternary phase diagrams were 2866
http://journals.cambridge.org
J. Mater. Res., Vol. 12, No. 11, Nov 1997
Downloaded: 15 Mar 2015
reported at the temperature range where the RE123 phase and the liquid were stable,2,10–13 which were not enough to fabricate R
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