Effect of high oxygen partial pressure heat treatment on the superconducting properties of Bi2Sr2CaCu2Ox/Ag tapes

Abstract

We investigated the effect of oxygen partial pressure pO 2 during melt-and-solidification heat treatment on the superconducting properties of grain oriented Bi-2212 thick films. T c and c-axis parameter decreased with increasing pO 2 , indicating the samples were in the over-doped state. The heat treatment temperature which gave highest J c increased with increasing pO 2 . This was explained by the increase of the solidification temperature of Bi-2212 with pO 2 . Both the resistive J c and intergrain J c estimated from the dc magnetization increased with increasing pO 2 when the samples were melt-solidified under an optimum condition for each pO 2 . Amplitude dependence of ac susceptibility suggested that the coupling of Bi-2212 grains was improved with increasing pO 2 . Irreversibility field B irr below ϳ60 K was also enhanced with increasing pO 2 . Low temperature annealing under high pO 2 after the melt-solidification also increased the oxygen content in Bi-2212 and hence B irr . However, the annealing did not change the amplitude dependence of ac susceptibility, and transport J c at 4.2 K was almost independent of the annealing. The results indicate that the increase of J c at 4.2 K with increasing pO 2 during melt-solidification is primarily attributed to the improvement of the grain couplings.

Bubble formation within filaments of melt-processed Bi2212 wires and its strongly negative effect on the critical current density

“…• C. Manipulation of the overall Bi2212 composition and changing the cooling rate are some ways to raise J c [7][8][9][10], but really much is still unknown about what controls J c in wires. Recently we compared the separate contributions of superconducting connectivity and flux pinning to J c by varying the cooling rate [11] through the Bi2212 phase nucleation in a through-process quench study.…”

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

“…and 885 "C for P02=0.01,0.21 and 1 atm, respectively [3]. The tapes were held at TmaX for 5 minutes, then cooled down at 10 K/hr for 5 hrs, and finally furnace-cooled to room temperature.…”

“…It was reported that the J, was influenced by oxygen partial pressure (Poz) during processing [3]-[SI. We reported that the J, values of Bi-2212/Ag tapes were 0.5, 1.2 and 2x105 Ncm2 (4.2 K,10 T) when processed in P02=0.01, 0.21 and 1 atm, respectively [3].…”

Development of high critical current density in multifilamentary round-wire Bi2Sr2CaCu2O8+δ by strong overdoping

“…Much discussion on improving conductor J c deals with manipulating the melt phase assemblages. 11 Here, we concentrate on the final portion of the heat treatment, which occurs after forming the Bi-2212 network, where we enhance the superconducting connectivity by slow cooling in an O 2 -rich atmosphere.…”