¹⁹⁷Au Mössbauer study of a gold-doped YBa₂Cu₃O_7-σ high-temperature superconductor

Abstract

A high temperature superconductor with the composition YBa₂Cu_2.9Au_0.1O_7−δ was studied by Mössbauer spectroscopy with the 77 keV gamma rays of¹⁹⁷Au, by X-ray diffraction, and by magnetization measurements. The main component in the Mössbauer spectrum, a quadrupole doublet with an isomer shift of +3.29 mm/s with respect to metallic gold and a quadrupole splitting of 3.61 mm/s, can be attributed to Au³⁺ in a square planar oxygen coordination, as is expected for gold replacing Cu(1). A further, weak doublet becomes dominant upon reduction of the specimen, and has an isomer shift of +3.46 mm/s and a quadrupole splitting of 7.12 mm/s. This component may be Au⁺ or Au³⁺ in an unusual coordination. Only a small fraction of the gold was found to be metallic in both the oxidized and the reduced state.