Growth of large superconducting Bi2+xSr2-yCuO6+δ single crystals by travelling solvent floating zone method

As-grown superconducting Bi2+xSr2-yCuO6+beta (Bi-2201) single crystals as large as 28 x 6 x 2.5 mm(3) have been successfully grown under high oxygen pressures by the traveling solvent floating zone technique. It was shown that the crystal growth habit is more sensitively affected by the starting composition than by the growth rate and the oxygen pressure, p(O-2), applied during the growth. The X-ray rocking curves around the (0 0 8) reflection demonstrate the high quality of the Bi-2201 crystals with mosaicity less than 0.15 degrees. The X-ray diffraction studies indicate that the Bi-2201 crystals possess the pseudotetragonal structure. The c-axis lattice parameter is influenced by both the Bi/Sr ratio and the p(O-2). The as-grown crystals show superconductivity except for those grown from the starting compositions with x = y = 0, x = y = 0.1 and x = y = 0.3, respectively. The superconducting transition temperature, T-C determined from magnetic susceptibility measurements varies from 3.5 to 8.5 K upon the Bi/Sr ratio and the p(O-2) applied. Transitions are sharp with DeltaT(C) < 1.0-1.5 K. The starting compositions of Bi2.2Sr1.9Cu1.2O6+beta and Bi2.35Sr1.98CuO6+beta were found to be suitable to grow large and superconducting Bi-2201 single crystals. (C) 2001 Elsevier Science BN. All rights reserved.