Crystal structure and superconductivity of Bi-2223

The crystal structure of the Bi₂Sr₂Ca₂Cu₃O_{10 + x} high-temperature superconductor is investigated by the X-ray Rietveld method. The results obtained are used to analyze the structural features of the bismuth high-temperature superconductors in respect to their superconducting properties. The refinement of the structure of the Bi-2223 compound in the four-dimensional space group A2aa (a00) 000 (Z = 4) with the vector q ～ 0.21a* does not reveal any indication of a modulated structure of the Bi-2212 type. The lattice parameters are 5.411(3), 5.409(1), and 37.082(1) Å. The agreement factors are R _wp = 8.10% and R _p = 5.49%. The results obtained are consistent with the notion that bismuth high-temperature superconductors are supercon-ductors with a more distorted crystal structure as compared to other representatives of high-temperature superconductors with critical temperatures T _c > 100 K. These distortions primarily manifest themselves in the segregation of the Bi and O ions of the “charge block” with the formation of zigzag chains that are characteristic of the structure of Bi₂O₃ and are stimulated in particular by defects in the calcium layer.