The effect of oxygen partial pressure during heat treatment on the microstructure of dip-coated Bi-2212/Ag and Ag alloy tapes

The evolution of the microstructure during heat treatment was investigated for dip-coated Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/(Bi-2212)/Ag and Ag alloy tapes as a function of temperature and oxygen partial pressure (P(O/sub 2/)=0.01, 0.21 and 1 atm) using quenched and fully-processed tapes. The microstructures were essentially the same for Bi-2212 on pure Ag and on the Ag alloy, Although the melting temperature of Bi-2212 increased with increasing P(O/sub 2/), the solidification temperature (T/sub sol/) of Bi-2212 for P(O/sub 2/)=0.21 atm was higher than that for P(O/sub 2/)=1 atm. The volume fraction and grain alignment of Bi-2212 processed in P(O/sub 2/)=0.01 atm was smaller than in tapes processed in 0.21 and 1 atm, which were quite similar. HR-TEM studies on grain boundaries and AC susceptibility measurements suggest that the higher critical current density(J/sub c/) for tapes processed in P(O/sub 2/)=1 atm than that for 0.21 atm is due to improved coupling of the grains.