A growth and annealing experiment concerning large crystals of Bi2Sr2CaCu2Oy with only a single domain

Annealing experiments in air have been performed on large crystals of Bi2Sr2CaCu2Oy with only a single domain, which were grown by a directional solidification method and are free from intergrowth defects, twins and, more importantly, showed sufficiently small mosaicity, it is found that after annealing at 450-650 degrees C, the Bi2Sr2CaCu2Oy crystals showed a very narrow diamagnetic transition width Delta T-c (< 1.5 K). Above this annealing temperature range, the annealed crystals, just like the as-grown crystals, showed a much broader diamagnetic transition. To explain these typical changes of Delta T-c with the annealing temperature, a selected crystal was progressively annealed in air at 500 and 750 degrees C for 4 and 8 h and full structural characterization by x-ray diffraction of the crystal as grown and after each annealing was conducted. Apart from variations in the cell parameters, it is evident that the crystal becomes highly oriented, corresponding to the extreme narrowness of Delta T-c.