GROWTH OF BI2SR2CACU2O8+X SINGLE-CRYSTALS AT DIFFERENT OXYGEN AMBIENT PRESSURES

Bi-2212 superconducting single crystals were grown by the travelling solvent floating zone method at different oxygen ambient pressures. Electron probe micro-analysis showed a systematic increase of the Sr/Ca ratio in the as-grown crystals with increasing oxygen ambient pressure and a maximal superconducting transition temperature of T(c-onset) = 95 K, and DELTAT(c), = 1.5 K was obtained for crystals grown at an oxygen ambient pressure of 200 kPa. Thermogravimetric and post-annealing experiments in air at 500 and 800-degrees-C have shown that the oxygen content and the T(c-onset) values in the crystal do not depend only on the annealing temperature, but also on its chemical composition. The in-field current density J(c) measured at 5 K on crystals grown al 200 kPa oxygen ambient pressure was considerably smaller than that of crystals grown in air.