An X-ray and neutron diffraction study of cation substituted TlSr 2CuO 5

Abstract

The structures of TlSr (2− x) La x CuO (5+δ), with x=0.5, 0.75 and 1, and Tl .5Pb 0.5Sr 2CuO (5+δ) have been examined with X-ray and neutron powder Rietveld refinement. They are isostructural (P4/mmm) with the corresponding thallium-barium cuprate having one Cu-O layer with Cu 3+ ions in octahedral coordination with oxygen (structure type 1201). The influence of cation substitution and disorder on the structure and superconducting properties of these phases have been investigated. La 3+ substitution for Sr 2+ stabilises the structure and reduces Cu 3+, permitting superconductivity, while Pb 2+ substitution for Tl 3+ only stabilises the structure, without reducing Cu 3+.