Structural Study of Superconducting Tl-Ba-Ca-Cu-O System

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Abstract
A crystal structure of Tl-Ba-Ca-Cu-O system with a superconducting onset transition temperature higher than 100 K which is systematically characterized by electron probe microanalysis and electron diffraction is determined by single crystal X-ray diffraction. The unit cell is described by a body-centered tetragonal lattice with space group I4/mmm. The structural unit consists of the seven oxide layers, -Ca-Cu-Ba-Tl-Tl-Ba-Cu-, stacked along the c-direction. The expected chemical formula is Tl1.95Ba2Ca0.85Cu2.18O8, which is slightly deviated from the stoichiometric composition Tl2Ba2CaCu2O8. It is suggested that the hole carrier of this system may be given by the nonstoichiometric composition of the cation.