EFFECT OF FLUX COMPOSITION ON CRUCIBLE CORROSION AND ALUMINUM DISTRIBUTION COEFFICIENT IN YBCO SINGLE-CRYSTALS

Crucible corrosion and the aluminum contamination effects in large single crystals of YBCO grown by long-duration flux-growth experiments were studied. It was found that the BaO/CuO ratio in the flux influences the corrosion: a minimum of aluminum is present in fluxes whose composition is near the BaO-CuO eutectic, and the corrosion increases at increasing concentration of either CuO or BaO with respect to the eutectic. In addition, at BaO concentration higher than the eutectic one, the distribution coefficient of aluminum between the crystals and the solution decreases. Crystals containing < 3% Al/Cu have been reproducibly grown: they exhibit T(c) greater-than-or-equal-to 90 K and DELTA-T(c) < 1 K.