Abstract
In order to synthesis the superconductive Bi-Sr-Ca-Cu-O ceramics, ultrafine powders were prepared by arc-melting, evaporation and deposition of Bi, Sr, Ca and Cu metals in the 50%Hz-Ar atmosphere at 0.1 MPa pressure ("hydrogen plasma-metal" reaction). Crystal structures of ultrafine powders obtained from Bi and Cu metals were found to be metallic phase of Bi and Cu. but in the case of Sr and Ca metals were found to be hydroxide compounds [Sr(OH)2 and Ca(OH)2] of Sr and Ca. The specific surface area of Bi, Sr(OH)2, Ca(OH)2 and Cu ultrafine powders determined by BET method were 2.1, 20.0, 25.5 and 7.8 m2/g, respectively.
The sintering and superconducting properties of Bi-Sr-Ca-Cu-O system (Bi:Sr:Ca:Cu = 4:3:3:6) were investigated by using a mixture of above ultrafine powders. DTA measurements indicated that the most favorable temperature range for solid-state sintering in air was between 830°C and 870°C, regardless of the mixed powders was calcined or not. When the mixed powder is sintered at the above temperature range for 3-5 h, a great amount of low Tc phase (80K) is formed in the sintered specimen, but sintering longer than about 20 h caused a decrease in low Tc phase and formation of a small amount of high Tc phase (110 K). It is found that high Tc phase is formed effectively by resintering of a compact prepared from the specimen including a great amount of low Tc phase.
