Superconductivity in the Bi2(Ca, Sr)n+1CunO2n+4 (n=1, 2, or 3) series: Synthesis, characterization and mechanism

The n=1, 2 and 3 members of the Bi2(Ca, Sr)n+1CunO2n+4 series of superconductors have been synthesized and characterized by a variety of techniques including electrical resistivity, magnetic susceptibility and non-resonant microwave absorption. Based on studies with a number of compositions, the T c ranges for the n=1, 2 and 3 members are suggested to be 60±20 K, 82±8 K, and 107±3 K, the rather broad ranges arising from differences in sample stoichiometry and homogeneity. Electron spectroscopic studies show that Cu is mainly in the 2 + and 1 + states suggesting the importance of oxygen holes.