A SERIES OF CRYSTAL STRUCTURES OF SUPERCONDUCTING PHASES IN TI-Ba-Ca-Cu-O SYSTEM

摘要

A series of superconducting phases has been synthesized by powder sintering in T1-Ba-Ca-Cu-O system and the crystal structures of these superconducting phases have been determined with the X-ray powder diffraction method. All of these superconducting phases belong to the tetragonal symmetry. They have the same lattice constant α but a different lattice constant c. The crystal structures of these superconducting phases are composed of two units, i. e. intercalation （single T1-Olayer or double T1-O layers） and oxygen deficient pseudo-perovskite unit Ba₂Ca_n-1Cu_nO_2n+1 （n is an integer）. These superconducting phases can be divided into two types. Type Ⅰcontains only one single T1-O layer as an intercalation with primary tetragonal lattice and space group P4/mmm. Type Ⅱ contains two T1-O layers in an intercalation with a body-centered tetragonal lattice and space group I4/mmm. The chemical formulas of Type Ⅰand Type Ⅱcan be generalized as TIBa₂ Ca_n-1 Cu_nO_2n+2.5 （n=1, 2, 3, 4） and T1₂Ba₂