Annealing experiment on high- superconductor Bi-2212 single crystals

Two different types of as-grown Bi 2 Sr 2 Ca 1 Cu 2 O 8+δ (Bi-2212) single crystals grown by a directional solidification and floating zone methods have been annealed in air and 1 atm of flowing oxygen at 500-800°C for 72 h followed by different cooling processes. Experimental results show that there are no change in composition or phase segregation caused by the annealing. Annealing of the single crystals grown by the directional solidification method increases the superconducting transition temperature T c from 70 K (as grown) to 83 K (annealed), with the superconducting transition width ΔT c (5-95% of complete superconducting transition) decreasing from 36 K to 12 K. Annealing of the single crystals grown by the floating zone method depresses T c from 91 K (as grown) to 83 K (annealed), with ΔT c increasing from 4 K to 7 K. Further, the annealing of the as-grown crystals results in increase of the superconducting volume fraction. The results show that oxygen content and distribution in the crystals play a key role in the superconductivity of these crystals. The quality of the as-grown crystals also affects the results of the annealing experiments.