Effect of oxygen partial pressure and melting temperature on Ag sheathed Bi-2212 wires

Abstract

A serious problem for Ag-sheathed Bi-2212 wires produced by a partial melt process is oxygen release which causes effluence of the oxide materials from the Ag sheath. Higher oxygen partial pressure during the melt process cuts the oxygen release. We investigated the effect of the oxygen partial pressure, melting temperature, and cooling rate on superconducting properties of Ag-sheathed wires. It was found that (i) the formation of the Bi-2212 phase under a higher oxygen partial pressure of 1 atm is slower than that with a lower oxygen partial pressure of 0.2 or 0.5 atm; therefore, the cooling rate should be as slow as 0.25 °C/min to get homogeneity of the intragrain superconductivity as well as formation of the Bi-2212 phase, and (ii) melting temperature should be just above the incipient melting point; otherwise, Jc significantly decreases due to the formation and growth of voids together with degradation of superconductivity.