Formation and growth mechanisms of Bi₂Sr₂CaCu₂O_yon an Ag substrate in the partial melting method

Abstract

We investigated the phase changes of a Bi-Sr-Ca-Cu-O/Ag composite tape during cooling from a partially molten state using the high-temperature X-ray-diffraction and oil-quenching techniques. In the cooling process, (SrCa)CuO2 and Bi(SrCa)2Oy appeared at the areas where the (SrCa)2CuO3 phase disappeared. At around 860 degrees C, these solid phases melted into the liquid phase, and then Bi2Sr2CaCu2Oy (Bi-2212) grew rapidly at the surface. First, nucleation of Bi-2212 occurred at the surface of the liquid phase. With decreasing temperature the Bi-2212 crystal growth proceeded slowly from the surface to the inner area with the a-b plane almost parallel to the surface. During the growth of Bi-2212, excess Bi was ejected from Bi-2212 and a thin Bi-enriched layer was formed at the growth front of Bi-2212.