Preparation and Chemical Composition of Superconducting Oxide Tl₂Ba₂Ca_n-1Cu_nO_2n+4 with n=1, 2 and 3

Superconducting oxides of Tl 2 Ba 2 Ca n -1 Cu n O 2 n +4 with n =1, 2 and 3 were synthesized, and their structure and chemical composition were examined by X-ray powder diffraction, EPMA, Rietveld analysis and electron microscopy. Partial substitution of Tl with Ca was confirmed, but the production of holes in Cu layers expected from this substitution was rather small for a 120 K superconductor. Charge transfer of Tl 3-δ -Cu 2+δ would provide both the hole in the Cu-O bond required for high T c and s-like electron of Tl atoms for stabilization of layered structures.