Crystal Growth of the High-T_c Superconductor in the Bi–Sr–Ca–Cu–O System

Abstract

Small disc-like grains of the low-T_c (80 K) phase in Bi-based superconductors grow to larger, plate-like crystals of the high-T_c (110 K) phase during heating at the temperature higher than 870°C. In the SEM images of polished sections some phases other than the superconductive ones are observed always in the process of the crystal growth. According to the EPMA measurement they are identified as following three; Ca₂CuO₃, in which about 8% of Ca are substituted by Sr, (Sr_1–z, Ca_z)₃Cu₅O_x (Z≅0.4), in which less than 2% of Bi is involved, and CuO. They show different colour under optical microscope. Based on the sequential change in their fraction it may be considered that Ca₂CuO₃ and/or (Sr_1–z, Ca_z)₃Cu₅O_x react with the matrix low-T_c phase to produce the high-T_c one.