FORMATION OF SUPERCONDUCTOR PHASES IN THE SOLIDIFICATION OF Bi-Sr-Ca-Cu-O MELT

摘要

Bi_2Sr_2Ca_2Cu_3O_x (2223) phase is not formed but Bi_2Sr_2Ca_2Cu_3O_x (2212) and Bi_2Sr_2CuO_x (2201) phases are observed during continuous cooling processes with the rates of 0.001 - 10 deg C/s. The time-temperature-transformation (Tm diagram in the solidification of the melt is proposed based on X-ray diffraction (XRD) analysis. The high-Tc superconductor phase 2223 is formed through isothermal treatments at 850 deg C for over 150 ks. The results of XRD and scanning electron micrograph with energy dispersive X-ray microanalysis for the isothermal treatment show that 2201 needles are crystallized at the interface between the (Ca, Sr)_2CuO_3 crystal and the retaking super cooled liquid, and then a part of the 2201 phases transforms to 2212 and 2223 phases by the diffusion of Ca, Sr, and Cu ions.