Phase Relations and Homogeneity Region of the HighTemperature Superconducting Phase (Bi,Pb)_2Sr_2Ca_2Cu_3O_(10+d)

摘要

For the nominal composition of Bi_(2.27-x)Pb_xSr_2Ca_2Cu_3O_(10+d), the lead content was varied from x = 0.05 to 0.45. The compositions were examined between 800 and 890℃ which is supposed to be the temperatue range over which the so-called 2223 phase (Bi_2Sr_2Ca_2Cu_3O_(10+d)) is stable. Only compositions between x = 0.18 to 0.36 could be synthezised in a single phase state. For x > 0.36, a lead-containing phase with a stoichiometry of Pb_4(Sr,Ca)_5CuO_d with a small solubiliy of Bi is formed, for x < 0.18 mainly Bi_2Sr_2CaCu_2O_(8+d) and cuprates are the equilibrium phases. The temperature range for the 2223 phase was found to be 800 to 890℃ but the 2223 phase has extremely varying cation ratios over this temperaure range. Former single phase 2223 samples turn to multiphase samples when annealed at slightly higher or lower temperaures. A decrease in the Pb solubility with increasing as well as decreasing temperature with a maximum at about 850℃ was found for the 2223 phase.