INFLUENCE OF TA DOPING ON THE GROWTH AND SUPERCONDUCTING PROPERTIES OF YBA2CU3O6+DELTA CRYSTALS

Single crystals of YBa2Cu3O6+delta, completely separated from flux, me asuring up to 5-6 mm2 and 0.25-0.5 mm thick, were grown reproducibly f rom BaCuO2 solutions containing 0.8 wt% Ta2O5, by the top seeded solut ion growth technique. Addition of Ta increases the crystal size due to reduced nucleation. The crystals exhibit a broad superconducting tran sition at 80 K when annealed in air (a narrow transition at 86 K on ox ygen annealing), attributed to the incorporation of stoichiometric exc ess of oxygen in the presence of Ta, as supported by the EDX, thermogr avimetry and oxygen titration analysis.