Correlation of structure and properties in Ba-doped Bi-2201 phase

The characteristic feature of electronic structure of the Ba-doped 2201 phase was studied by electron diffraction XPS and UPS spectra. The study on its superconductivity shows that the appropriate substitution of Ba for Sr (x≤0.2) can raise the T_c of 2201 phase; but as x exceeds 0.3, T_c decreases sharply, simultaneously accompanied with the superconductor-insulator transition. Based on all these experimental results, the relation between incommensurate modulation structure, electronic structure and superconductivity for the Bi-2201 phase were discussed comprehensively. It was found that the replacement of Ba²⁺ for Sr²⁺ intensifies the mismatch between Bi-O layers and perovskite blocks and the enhancement of this mismatch finally leads to the variation of electronic state of Cu3d hence leads to the transition from superconducting to insulating phase.