Yttrium Barium Copper Oxide High Temperature Superconductors: from Bulk Material to Superconductive Wire and Tapes.

The solid state reaction method or the "dry route" was used for the synthesis of superconductive Y Ba _2{rm Cu}_3{rm O}_{rm 7-x} bulk material. From a stoichiometric powder mixture (1/2 Y_2 {rm O}_3 + 2 BaCO _3 + 3 CuO), the superconductive Y Ba _2{rm Cu}_3{rm O}_{rm 7-x} phase is formed by an appropriate thermal treatment. The thermal treatment consists of two steps. During sintering, the BaCO_3 will be calcined and the mixture of oxides will react to form the 1-2-3 perovskite structure at high temperature (T > 900 ^circ{rm C}). A thermal treatment in oxygen (annealing) is necessary to transform the tetragonal Y Ba_2{ rm Cu}_3{rm O}_6 to the orthorhombic Y Ba_2{ rm Cu}_3{rm O}_ {rm 7-x} (x ~ 0) structure. The critical temperature of this material is about 90 K. A powder-in-binder technique followed by phase inversion was developed to make wires (by suspension spinning) and tapes (by the Doctor Blade method) from this ceramic material. The binder (the organic polymer: polysulfone) is removed by an adapted thermal treatment. The wire is then sintered and annealed to restore the superconductive phase. The superconducting properties (critical temperature and critical current) were determined by transport current and ac susceptibility measurements. A peritectic thermal treatment was developed to improve the microstructure of the samples. Better intergranular connections are formed by the partial melting of the Y Ba_2{rm Cu}_3{ rm O}_{rm 7-x}. With this peritectic thermal treatment the quality (especially the critical current density (J_{rm c})) of the samples and the reproducibility of the results are enhanced. ftn^2This research was sponsored by the European Community in the framework of a BRITE/EURAM programma (BE-0139).