Formation of BaCeO 3 and its influence on microstructure of sintered/melt-textured Y-Ba-Cu-O oxides with CeO 2 addition
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Hong-Chul Moon and Dong-Soo Suhr Department of Materials Science and Engineering, Choongnam National University, Daeduk Science Town, Daejon, 301-764, Korea
S. H. Lai and P. J. McGinn Center for Materials Science and Engineering, Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (Received 13 December 1993; accepted 16 March 1994)
The formation of BaCeO 3 and its effects on microstructure were studied in sintered/melt-textured Y - B a - C u - 0 oxides containing 5 wt. % CeO2 and various amounts of Y 2 Ba 1 Cu 1 0 5 . The added CeO 2 was converted to fine particles of BaCeO 3 near 930 °C, which is the conventional sintering temperature for Y - B a - C u - O . Y 2 BaiCui0 5 and CuO are formed as by-products of the reaction between CeO 2 and Y1Ba2Cu307_3, phase. The CeO 2 addition reduced the particle size of Y 2 BaiCui0 5 which was trapped in the YiBa 2 Cu 3 0 7 - y matrix after the melt-texture growth. During the peritectic decomposition stage of Y 1 Ba 2 Cu 3 0 7 - ) , phase into Y 2 Ba 1 Cu 1 0 5 and liquid phase, the morphology of the decomposed Y 2 BaiCui0 5 was changed from a blocky shape in the undoped sample to an acicular shape of high anisotropy in the CeO2-added sample. The formation of the highly anisotropic Y 2 BajCui05 particles appears to be responsible for the refinement of Y 2 BaiCui0 5 particle after the melt-texture processing.
I. INTRODUCTION A number of studies have been carried out for the microstructural modification of high-Tc YiBa 2 Cu 3 0 7 _ > , (1-2-3) superconductor because the current-carrying properties highly depend on the characteristics of its microstructure. For example, grain alignment to the direction of current path showed high critical current density (/ c ) exceeding 104 A/cm 2 at high magnetic fields.1"3 The weak link property of the grain boundary, which is a main barrier for the current transport, can be eliminated through the alignment of superconducting grains normal to the c-axes of the crystal. With the aligned microstructure, the addition of second impurity phases, such as Y 2 Ba!Cui0 5 , 4 BaSnO3s,3 and its influence on microstructure
The present paper is aimed toward understanding microstructural changes in the Y - B a - C u - O system when CeO2 is added. We report the formation of BaCeO 3 and its influence on microstructure, especially on the particle shape and size of 2-1-1, of the Y - B a - C u - O superconductors prepared by the melt-texture processing. II. EXPERIMENTAL PROCEDURE The 1-2-3 powder used in these experiments was prepared by the conventional solid-state reaction method using Y 2 O 3 , BaCO 3 , and CuO powders of 99.9% purity. For uniform mixing, the powder mixture of 1-2-3 composition was ball-milled in ethanol solution for 10 h. The ball-milled powder was dried and calcined at 920 °C for 24 h in air and then air-cooled. The crushing step followed by calcination was repeated to enhance the formation of the 1-2-3 phase. The 2-1-1 powder was prepared in the same way as that for the 1-2-3 powder and calcined at
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