INFLUENCE OF TA ON THE MORPHOLOGY AND SUPERCONDUCTING PROPERTIES OF YBA2CU3O6+DELTA SINGLE-CRYSTALS

Single crystals of YBa2Cu3O6+delta doped with Ta2O5 have been grown by the top seeded solution growth (TSSG) technique in re-crystallized alumina crucibles using BaCuO2 as the solvent and oriented sapphire rod as a substrate to nucleate a seed. Single crystal plates, completely separated from flux, measuring up to 5-6 mm square and 0.5 mm thick were grown with sufficient reproducibility. Addition of Ta helps in modifying the crystal habit by increasing the thickness and size of the crystals along the c-axis. Gradient transport has been employed to improve the diffusion of YBa2Cu3O6+delta towards the growing crystal. The crystals are not twinned and exhibit a superconducting transition at 80 K after annealing in air at 350-degrees-C for 10 hours. Improved superconducting behavior is attributed to the incorporation and stabilization of stoichiometric excess of oxygen in the presence of pentavalent Tantalum, which is confirmed by the thermogravimetric measurements and oxygen titration analysis.