Effect of Silver on the Sintering Characteristics of High T Ceramic Superconductors

Abstract

A detailed investigation on the densification behaviour of Y-Ba-Cu-oxide (YBCO)-AgX and Bi-Pb-Sr-Ca-Cu-oxide (BPSCCO)-AgX composite powder synthesised by a chemical pyrophoric decomposition technique is made. It has been observed that Ag plays a significant role on the lowering of sintering temperatures and melting points of these superconductors. In YBCO-AgX, for 0< x<_0.6 the rate of densification increases and for 0.6<x<1.2 the rate of densification decreases. The densification behaviour is due to oxygen absorption at the interface of YBCO and Ag grains and a low temperature eutectic Ag,,OX formed which promotes liquid phase sintering. Studies on the sintering characteristics under inert atmosphere indicate increased densification with the silver addition. The removal of oxygen from Ag,OX to the inert sintering atmosphere enhances the densification rates . This is also confirmed from the weight loss of the pellets observed in the TG experiments. Sintering studies of BPSCCO-AgX composites show decrease of densification with the Ag content in the matrix. The degradation of superconducting properties is attributed to the change of chemical compositions of the composites. The evaporation loss of Bi, Pb, Sr and Cu during sintering is observed to be the cause of degradation. The evaporation losses are increased with x.