Correlation between Cu valence, hole density and Tc of Bi2201, Bi2212 and Bi2223 superconductors

For the Bi2201 phase, by comparing the correlation between them with the Mott-Hubbard split model, it was found that while the correlation deviates from the Mott-Hubbard model for air-sintered samples, the correlation agree well with the Mott-Hubbard model for.Ar-annealed samples. The deviation is believed to come from the destruction of the Mott-Hubbard character. For the air-annealed samples of Bi2212 phase, hole concentration,,p scales very well with v, and the p-v line passes through the origin of the coordinates. However, the proportional constant is about two. The simplest explanation of the double proportional constant is to assume the coexistence of a hole of CuO2 character and BiO character. For the Bi2223 phase, only an Ar-annealed sample lied on the p = v line, suggesting that it has a Mott-Hubbard like electronic structure. However, the air-sintered and oxygen-annealed samples deviated unexpectedly far from the p = vline, indicating charge balance in the sample is drastically changed in the system. We made an accurate Tc vs v and Tc vs p diagrams for the Bi-based superconductors. While the Tc vs v diagram for the Bi2201 and 2212 superconductors showed a bell-shape, the Tc vs p diagram for those superconductors had a wide plateau on the rep. The puzzling shape of Tc vs p diagrams is also explained by the two hole model. Around the plateau, mainly the number of hole of the BiO character is changed. (C) 1998 Elsevier Science Ltd. All rights reserved.