Direct observation of gold valence change as a function of oxygen stoichiometry in YBa2Cu3−yAuyO7−δ
- 12 April 1993
- journal article
- research article
- Published by AIP Publishing in Applied Physics Letters
- Vol. 62 (15) , 1827-1829
- https://doi.org/10.1063/1.109562
Abstract
A study of the Au197 Mössbauer resonance is reported as a function of oxygen stoichiometry for gold‐doped YBa2Cu3O7−δ. Three separate Mössbauer features are identified and correspond respectively to gold metal particles, Au3+ in a square‐planar Cu(1) site, and Au+ in a two‐ligand c‐axis coordinated Cu(1) site. All the gold successfully incorporated into the 123‐structure is trivalent at full oxygenation (O7.02) but is reduced as a function of decreasing oxygen content until only monovalent gold remains at the orthorhombic to tetragonal transition (≊O6.4). A significant fraction of the Au3+ in the oxygenated sample resides near grain boundaries and is precipitated as gold particles upon reduction. The observation of monovalent gold in the reduced sample is the first report of the existence of Au+ with uniquely oxygen coordination for any material.Keywords
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