Growth and Annealing Effect on Resistive Anisotropy of Bi2Sr2CaCu2O8 Single Crystals

Abstract

High quality, large size Bi2Sr2CaCu2O8 (Bi-2212) single crystals have been grown by a self-flux method in a horizontal temperature gradient. We found that the presence of the horizontal temperature gradient is helpful for the crystal growing along the ab-plane direction. However, non-uniform distribution of temperature in the vertical direction in the furnace often causes imperfections along the c direction. This may be one of the critical reasons why crystals produced by flux method are very thin and easy to cleave along the ab-plane, compared with the crystals grown by the floating zone method. The influence of the growth conditions and post-heat treatment on the resistivity anisotropy of the crystals has been investigated. Crystals grown in the condition where the temperature is non-uniformly distributed along the vertical direction often have higher anisotropy in resistivity. In addition, the post-heat treatment in the nitrogen atmosphere reduces the anisotropy of the resistivity of the crystal. Possible mechanisms are discussed.