The effects of oxygen on melt-processing Ag-sheathed Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>8</sub> conductors
W Zhang; E E Hellstrom; W Zhang; Appl. Superconductivity Center, Wisconsin Univ., Madison, WI, USA; E E Hellstrom; Appl. Superconductivity Center, Wisconsin Univ., Madison, WI, USA
Журнал:
Superconductor Science and Technology
Дата:
1995-06-01
Аннотация:
The phase assemblages that form when Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>8</sub> (2212) incongruently melts have been studied as a function of temperature and partial pressure of O<sub>2</sub> in the surrounding atmosphere. The critical phase assemblage for melt processing is the one present when 2212 begins to form from the melt on cooling. Between 0.001 and 0.01 atm O<sub>2</sub> the key phase in this assemblage is Bi<sub>2</sub>(Sr,Ca)<sub>3</sub>O<sub>3</sub>, from 0.075 to 0.30 atm O<sub>2</sub> it is (Sr,Ca)CuO<sub>2</sub>, and from 0.40 to 1 atm O<sub>2</sub> it is (Sr,Ca)<sub>14</sub>Cu<sub>24</sub>O<sub>x</sub>. The range from 0.40 to 1 atm O<sub>2</sub> is advantageous for melt processing as shown by the homogeneity of the microstructure of fully processed tape and the higher J<sub>c</sub> of tapes processed in 1 atm O<sub>2</sub>.
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