Transmission-electron-microscopy study of high-temperature superconducting phases in the Tl-Ba-Ca-Cu-O system

Two phases have been identified by convergent-beam electron diffraction in multiphase compounds of ${\mathrm{TlBaCaCu}}_3$ ${\mathrm{O}}_{6.5}$ with a superconductivity temperature of 114 K. They are subsequently found to be superconducting at 120.3 and 90.0 K. These phases are tetragonal with point group 4/mmm and lattice parameters of a=0.547 nm; c=3.61 nm and a=0.547 nm, c=2.97 nm, respectively. We have found by high-resolution lattice imaging that the 3.61 and 2.97 nm phases form coherent intergrowths. Both ordered and disordered intergrowths have been observed.