Synthesis of superconducting Bi2Sr2CaCu2O8+δ single crystals using alumina crucibles with different purities

A self‐flux method is the simplest technique for synthesizing Bi₂Sr₂CaCu₂O_8+δ (Bi‐2212) superconducting single crystals. However, the crystals are inevitably contaminated because of the Bi‐2212 stoichiometric melt reacting with the crucible material. In this paper, we investigate the nonsuperconducting subproduct that forms during heating in the self‐flux method for synthesizing Bi‐2212. This subproduct was identified as BiSr₂CaAl₃O₉ by X‐ray diffraction. Bi‐2212 crystal growth was performed using A1₂O₃ crucibles with three different purities (nominally 97, 99.7, and 99.9%). For both the 97 and 99.7% purity crucibles, the subproduct was observed in all five samples out of five, whereas for the 99.9% purity crucible, it was observed in only two samples out of five. Furthermore, the 99.9% purity crucible gave a much lower subproduct volume than the 97% purity crucible. The average superconducting critical temperature (T_c,zero) varied depending on the crucible purity; it was 89.6, 90.8, and 91.8 K for the 97, 99.7, and 99.9% purity crucibles, respectively. Finally, we fabricated Bi‐2212 stacked devices with intrinsic Josephson junctions (Bi‐2212 stack) using as‐grown crystals from the 97 and 99.9% purity crucibles. The Bi‐2212 stacks exhibited a highly hysteretic current–voltage characteristic even at liquid N₂ temperature and they had identical quality parameters for Josephson junctions (i.e., I_r/I_c and voltage jump V_j). We conclude that the subproduct formation has little effect on the electrical characteristics of a Josephson junction device at 77 K. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.