Growth of multi-millimeter wide single crystal platelets of YBCO and variation of their properties under thermal annealing in oxygen

Single crystals of the high temperature superconductor "YBCO" (YBa2Cu3O7-x), sized up to about 4×2.5×0.1 mm3, and therefore suitable for a large number of experimental investigations, have been grown by "flux" method, both in oxygen atmosphere and in air, using as a solvent the eutectic of two of the constituent oxides, namely Cu072%-1bBa028%. These crystals have been characterized by X-ray diffraction, d.c. resistivity and by a.c. susceptibility measurements both in the as-grown state and after various annealing cycles in oxygen atmosphere. the critical temperature Tc in the as-grown state ranges between 50 and 70 K, being on the average about 10 K higher for the crystals grown in oxygen atmosphere. Very sharp resistive transitions at 92 K were obtained after suitable annealing tratments in oxygen. The final oxygen contents per formula unit of YBCO were deduced from the values of the c lattice parameter. The dependence of Tc on the oxygen content resulted similar to the polycrystalline case.