Structure Analysis of the Bi2(Sr, Ca)3Cu2O8.2 Superconducting Crystal Based on the Computer Simulation of HRTEM Images

Abstract
The crystal structure of the high-T c superconducter, Bi2(Sr, Ca)3Cu2O8.2, is analyzed based on HRTEM images with help of the computer simulation. The structural modulation is approximated by the combination of supercells with different sizes. For the major supercell with lattice parameters, a=5.4 Å, b=5b s=27.0 Å and c=30.8 Å (Amma, orthorhombic), the coordinates and the occupational probability of cations are determined. In the Bi-deficient bands of Bi2O2 sheets, about 40% sites of Bi are statistically substituted by Sr. In the perovskite-like layer, Sr are partly replaced by Bi near the Bi-concentrated bands, while wholly by Ca near the Bi-deficient bands. In the Ca plane about 30% sites of Ca are replaced by Sr.