Large single crystals of yttrium barium cuprate superconductors were grown using a molten salt flux consisting of an equimolar mixture of NaCl and KCl. As produced, the crystals have a large oxygen deficiency corresponding to δ=0.5. However, they are orthorhombic and show superconducting behavior. Oxygen annealing effects are visible in the unit cell parameters and in an increased sharpness of the onset of the superconducting transition observed by a.c. susceptibility measurements. The resistive and magnetic behaviors are consistent with a range of oxygen deficiencies in the samples, even after oxygen annealing.
