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Influence of the spacing of Cu-O2 sheets on the superconducting transition temperature

Relationships between Tc and crystal structures of copper-oxide superconductors are examined from the view point of the interaction between Cu-O2 sheets. The Tc correlates with the Cu-Cu distance between the different Cu-O2 sheets, and there is a critical length around 4-6 AA. For longer distances, the Tc are less than 50 K. For shorter distances, on the other hand, the Tc are distributed from 50 to 125 K. In the latter case, Tc seems to linearly decrease with the Cu-Cu distance.