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We have discovered a new high- T c oxide superconductor of the Bi-Sr-Ca-Cu-O system without any rare earth element. The oxide BiSrCaCu 2 O x has T c of about 105 K, higher than that of YBa 2 Cu 3 O 7 by more than 10 K. In this oxide, the coexistence of Sr and Ca is necessary to obtain high T c .
Maeda et al. (Mon,) studied this question.