The authors have in situ grown Bi-Ca-Sr-Cu-O films by ac sputtering. The substrates were heated to 630-670 degrees C during ac sputtering. The sputtering was first carried out in a mixture of Ar(70%) and O2(30%) at a pressure of 0.2 mbar. Then the mixture of Ar(70%) and O2(30%) was replaced by pure O2 and the sputtering was kept for another one hour. Superconducting Bi2CaSr2Cu2Oy (2122) films with zero resistance at 70-75 K can be reproduced. The critical fields of the as grown films parallel to c-axis and ab-plane has been measured. The estimated zero temperature coherence lengths are zeta c=3.3 AA and zeta ab=36.1 AA respectively for the (2122) phase.
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