OXYGEN STOICHIOMETRY AND THE STRUCTURE OF TL2BA2CA2CU3O10-Y - A HIGH-RESOLUTION POWDER NEUTRON-DIFFRACTION STUDY

Samples of Tl2Ba2Ca2Cu3O10-y have been prepared with three different oxygen stoichiometries by reaction under various oxygen gas partial pressures. Powder neutron diffraction studies on these materials show that for y > 0 oxygen vacancies exist in the thallium-oxygen layer; filling this site results in a contraction of the lattice with concomitant reduction in the apical Cu-O bond length but with an expansion of the copper-oxygen interlayer distance. These structural changes which occur as a function of oxygen content are discussed in terms of the superconducting properties of these materials.