  This paper reviews the usual techniques for producing YBCO-type
single-domains and the microstructure of the as-obtained samples. The problems
of seed dissolution and parasite nucleations are discussed in details.
Formation of microstructural defects, such as pores and cracks, are 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, Sm, Dy, Gd, Eu or a
mixture of them. Generally Nd4Ba2Cu2O10 is preferred to Nd2BaCuO5] on the
microstructure and properties of RE-Ba-Cu-O single-domains. Trapping/Pushing
theory is described in order to explain the spatial distribution of RE-211
particles in the RE-123 [(RE)Ba2Cu3O7-d] monoliths. 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 on 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.
