Comparative study of Tl-2201 single crystals with T_c=30 and 110 K by means of X-ray structural analysis and NMR.

Abstract:
The crystal structure of a tetragonal single crystal of Tl-2201 with T_c=30 K has been determined by the X-ray diffraction technique (a = 3.8717(3), c = 23.224(3)  Angstrom, space group I4/mmm, Z = 2). The chemical composition is found to be Tl_1.90(1)Cu_0.10(1)Ba₂CuO_6.18(4). Displacements of Tl and O3 atoms from their symmetric sites have been observed. Structural parameters of Tl-2201 cuprates with various T_c have been compared. The superconducting transition temperature is shown to correlate most strongly with the parameter c, with the length of the bond between Cu and apical oxygen as well as with the distance between Ba²⁺ and the cuprate plane.