Modulated Structures in Superconductor Tl-Ba-Ca-Cu-O Oxides: Crystal Structure of Tl2Ba2CuO6+x Phase

Abstract

A crystal structure of Tl₂Ba₂CuO_6+x oxide, which was not a superconductor, was studied by an electron microscope. The unit cell parameters are a=b=3.85 Å and c=23.02 Å. The crystal was found to be one of a series of compounds expressed by Tl₂Ba₂Ca _n Cu _n+1O_2(3+n)+n in Tl-Ba-Ca-Cu-O (TBCCO) oxide systems. The crystal has an incommensurate superstructure modulation in the (100) planes, whose occurrence is different from the (110) plane modulation found in Bi-Sr-Ca-Cu-O (BSCCO) systems. The modulation takes place in the BaO-TlO-TlO-BaO slabs with a period 6.6×a along the [100] direction.