FIXED TRIANGLE IN Bi_2-XPb_XSr₂CaCu₂O_8+Y AND Bi_2-XPb_XSr₂Ca₂Cu₃O_10+Y SYSTEMS

Abstract

The structural characteristics of Bi 2-x Pb x Sr 2 CaCu 2 O 8+y ( Bi -2212) and Bi 2-x Pb x Sr 2 Ca 2 Cu 3 O 10+y ( Bi -2223) with x changing from 0 to 0.8 were studied by X-ray diffraction and Rietveld refinement. By careful calculation of chemical bond lengths and angles, it is found that there exists a fixed triangle on the Cu–O planes in the two systems, and then makes the Cu–O planes stable. The fluctuations of this fixed triangle were investigated, and it is found that there is a close relationship between it and T c 's. In addition, we discussed the origin of this special local structure. It may be caused by the interaction between the perovskite block and the rock salt block in a unit cell, which may play an important role in the mechanism of high temperature superconductivity.