Crystal growth and superconductivity of heavily La-doped Bi-2201 single crystals

A number of La-doped Bi-2201 single crystals were prepared by self-flux met hod. The qualities of the crystals have been checked by X-ray diffraction p atterns (XRD) and electron diffraction patterns from transmission electron microscopy (TEM). The correlation between the actual composition of La dete rmined by Energy-Dispersive X-ray (EDX) analysis and the c-axis parameter d etermined from XRD shows a linear behavior, being consistent with previous reports. A new superconducting phase with T-c as high as 36 K has been disc overed for the first time in heavily La-doped Bi2Sr2-xLaxCuO6+y single crys tals (x greater than or equal to 0.8) in which one normally could not obser ve the superconductivity. Since our samples have been post-annealed in flow ing oxygen and heavily La-doped samples are normally in the region with an antiferromagnetic background, it is natural to attribute the appearance of the high T-c superconductivity to the electronic phase separation induced b y the cooperative interactions between the antiferromagnetic background and the mobile holes (given by excess oxygen). (C) 1998 Published by Elsevier Science B.V. All rights reserved.