THE STRUCTURE OF TLBA2CA3CU4O11

The structure of the four cuprate layer superconducting oxide T1Ba2Ca3 Cu4O11 has been determined for the first time; a multiphase profile me thod was used to refine powder X-ray diffraction data collected from a sample containing 1234 as the only superconducting phase. Separations of the four cuprate layers are 3.174 (X2) and 3.200 Angstrom. As in o ther single thallium layer materials from the T1Ba2Can-1CunO2n+3 homol ogous series the TlO6 layers show a disordering of the thallium ions, giving rise to strongly distorted T106 octahedra, and a small level of substitution of thallium at the calcium sites is implied. The layer s eparations in 1234 and the average copper oxidation state indicate tha t the as-prepared material is close to optimised in terms of its struc ture for obtaining a high T-c.