From RE-211 to RE-123. How to control the final microstructure of superconducting single-domains

This paper reviews the usual techniques for producining YBCO-type single-domains and the microstructure of the as-obtained samples. The problems of seed dissolution and parasite nucleations are discussed in detail. The formation of microstructural defects, such as pores and cracks, is examined. An important part of this review is devoted to the study of the influence of RE-211 particles (RE2BaCuO5 where RE denotes Y, Yb, Nd, Sin, Dy, Gd. Eu or a mixture of them. Generally Nd4Ba2Cu2O10 is preferred to Nd2BaCuO5) for the microstructure and properties of RE-Ba-Cu-O single-domains. Pushing/trapping theory is described in order to explain the spatial distribution of RE-211 particles in the RE-123 ((RE)Ba2Cu3O7-delta) monoliths. The formation of RE-211-free regions is discussed. Different ways to limit the RE-211 coarsening are reviewed. Microstructural defects in the RE- 123 matrix caused by the RE-211 particles are presented. It is also shown that RE-211 particles play a significant role in the mechanical properties of single-domain samples. We finish this review by discussing the infiltration and growth process as a good technique to control the microstructure.