Fabrication of Bi2Sr2CaCu2O x and Bi2Sr2Ca2Cu3O x Superconductor Thick Films by Using Cu-Free Precursors on Ni Substrates

摘要

We studied the formation of Bi2Sr2CaCu2O x (Bi-2212) and Bi2Sr2Ca2Cu3O x (Bi-2223) thick films in a heat treatment process of the Ni-sheathed Bi-Sr-Ca-Cu-O (BSCCO) system. Cu was electrodeposited initially on the Ni substrates (Cu/Ni). Well-oriented Bi-2212 superconductor thick films were formed successfully on Ni tapes by liquid reaction between Cu-free precursors and Cu/Ni tapes. However, only a small amount of Bi-2223 was formed. Thick films were prepared by screen-printing with Bi2O3, SrCO3, and CaCO3 powders on Cu/Ni tapes and heat treating them. Heat treatment was performed in the temperature range of 750–850°C in a tube furnace for several minutes to hours. The phases and the microstructures of the high temperature superconductor thick films were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Electrical properties were examined by the standard four-probe method. At the heat treatment temperature, the specimens were in a partially molten state during reaction between the oxidized copper layer and the screen-printed precursors on the Cu/Ni tapes.