CORRELATION BETWEEN CU VALENCE, HOLE DENSITY AND TC OF BI2201, BI2212AND BI2223 SUPERCONDUCTORS

For the Bi2201 phase, by comparing the correlation between them with t he Mott-Hubbard split model, it was found that while the correlation d eviates from the Mott-Hubbard model for air-sintered samples, the corr elation agree well with the Mott-Hubbard model for.Ar-annealed samples . The deviation is believed to come from the destruction of the Mott-H ubbard character. For the air-annealed samples of Bi2212 phase, hole c oncentration,,p scales very well with v, and the p-v line passes throu gh the origin of the coordinates. However, the proportional constant i s about two. The simplest explanation of the double proportional const ant is to assume the coexistence of a hole of CuO2 character and BiO c haracter. For the Bi2223 phase, only an Ar-annealed sample lied on the p = v line, suggesting that it has a Mott-Hubbard like electronic str ucture. 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 v s v and Tc vs p diagrams for the Bi-based superconductors. While the T c vs v diagram for the Bi2201 and 2212 superconductors showed a bell-s hape, 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 o f the BiO character is changed. (C) 1998 Elsevier Science Ltd. All rig hts reserved.