CRYSTAL-STRUCTURE OF THE HIGH-TEMPERATURE SUPERCONDUCTOR TL2BA2CACU2O8

The authors present x-ray diffraction data for a single crystal of the newly identified superconducting phase, Tl//2Ba//2CaCu//2O//8, which has an onset temperature of approximately 112 K. The crystal structure, based on a body-centered tetragonal cell with a equals 3. 8550(6) A and c equals 29. 318(4) A (space group I4/mmm) is essentially the same as that of Bi//2Sr//3// minus //xCa//xCu//2O//8 and comprises double copper-oxygen sheets alternating with double thallium-oxygen layers. There are Ca**2** plus cations between adjacent Cu-O sheets and Ba**2** plus cations between the Cu-O and Tl-O layers. The copper-oxygen chains present in YBa//2Cu//3O//7 are absent in Tl//2Ba//2Cu//2O//8.