Short-range ordering due to displacements of thallium and oxygen atoms in superconducting Tl₂Ba₂CaCu₂O₈ observed by pulsed-neutron scattering

Abstract

The atomic positional correlations in superconducting Tl₂Ba₂CaCu₂O₈ were studied by pair-distribution-function analysis of the pulsed-neutron scattering data. The results show for the first time strongly correlated local displacements of both thallium and oxygen atoms in the Tl-O plane from the high-symmetry crystallographic sites. As a consequence of the displacements Tl atoms form chains or pairs accompanied by displacement of nearby oxygen atoms, resulting in locally orthorhombic order. The ordering, however, remains very much short range and does not alter the average symmetry. The implications of these results with regard to the superconductivity of these oxides are discussed.