Unexpected effects of gold on the structure, superconductivity, and normal state of YBa2Cu3O7

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Abstract
Using high‐resolution x‐ray and neutron diffraction measurements, we have shown that gold can be doped into YBa2Cu3O7 (1:2:3) up to 10% per formula unit, exclusively at the Cu(1) sites. Au doping causes a larger uniaxial expansion along the c axis, accompanying an increase in the Cu(1)—O(1) bond length and a decrease in the Cu(2)—O(1) bond length. The superconducting transition temperature (Tc) is enhanced upon Au doping and the normal‐state transport properties are altered even for small levels of Au doping. The widely held belief in the inert nature of Au with regard to high Tc superconductors is therefore invalid. These findings also raise questions concerning results using single crystals grown from gold crucibles.