FACTORS AFFECTING THE GROWTH OF SINGLE-CRYSTAL FIBERS OF THE SUPERCONDUCTOR BI2SR2CACU2O8

While short sections of single crystal fibers of the 85 K bismuth compound superconductor can be produced by the miniaturized laser-heated float zone process, it is much more difficult to produce extended lengths without the introduction of additional grains. Part of the problem is related to the peritectic nature of the material. Detailed studies have been performed to determine the influence of growth rate, seeding, and laser power (melt temperature) fluctuations on grain structure and second phase inclusions in fibers grown from a Bi2.1Sr1.8Ca1.1Cu2O(x) starting material. It was found that as the fiber diameter decreases, the maximum allowable growth rate increases due to an increase in the axial temperature gradient. Thermal fluctuations were shown to introduce CaO inclusions. Grain structure is not altered unless the fluctuations produce a large amplitude diameter variation. Several seeding techniques are discussed.