Correlation between oxygen excess density and critical transition temperature in superconducting Bi-2201, Bi-2212 and Bi-2223

It is suggested that oxygen excess in undoped material of the high temperature superconducting bismuth family creates periodic two-dimensional Cu3+Cu3+-ion patches in the copper–oxygen planes. These nanostructures have a size of 3.6nm square and show a strong linear relationship to their critical transition temperatures TcTc.