Structure and superconducting properties of the Tl1 –δ CaBa2Cu2O7 and Tl1 –δY1 –xCaxBa2Cu2O7 series
Superconducting Tl1 –δCaBa2Cu2O7 can be prepared without impurity from the corresponding two Tl–O layer cuprate only when some Tl deficiency is incorporated. The Tl1 –δCaBa2Cu2O7 and Tl1 –δY1 –xCaxBa2Cu2O7 series show maximum Tc at an optimal hole concentration. The Tc maximum occurs at a Cu—O distance of ca. 1.924 Å.