Abstract
New melt textured REBa 2Cu 3O 7/RE ′ 2 BaCuO 5 composites, have been obtained by top seeding melt-texturing growth. Two different starting mixtures of REBa 2Cu 3O 7 superconducting powders and insulating Y 2BaCuO 5 phase were used. On one hand RE is a natural mixture of heavy rare earth elements (Y, Yb, Lu, Er, Dy, Tm, Ho) extracted from the Brazilian mineral “Xenotime”, and on the other hand, RE is thulium. In both cases melt textured REBa 2Cu 3O 7/RE ′ 2 BaCuO 5 composites have been obtained where RE and RE ′ are different mixtures of heavy rare earth/yttrium and Tm/yttrium. The composition analysis shows different areas within the RE ′ 2 BaCuO 5 as a consequence of an inhomogeneous RE distribution, due to the differential solubility of each rare earth in the high temperature semisolid state. During the crystallization process a profound inversion of the rare earth composition between the superconducting matrix and the insulating precipitates occurs. Yttrium is selectively located in the 123 matrix and RE in the 211 particles. Heavy RE ions can substitute yttrium in MTG REBCO without degradation of the superconducting properties. A model for the crystallization process is proposed.
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