AU-197 MOSSBAUER STUDY OF A GOLD-DOPED YBA2CU3O7-DELTA HIGH-TEMPERATURE SUPERCONDUCTOR

A high temperature superconductor with the composition YBa2Cu2.9Au0.1O 7-delta was studied by Mossbauer spectroscopy with the 77 keV gamma ra ys of Au-197, by X-ray diffraction, and by magnetization measurements. The main component in the Mossbauer spectrum, a quadrupole doublet wi th an isomer shift of +3.29 mm/s with respect to metallic gold and a q uadrupole splitting of 3.61 mm/s, can be attributed to Au3+ in a squar e planar oxygen coordination, as is expected for gold replacing Cu(1). A further, weak doublet becomes dominant upon reduction of the specim en, and has an isomer shift of +3.46 mm/s and a quadrupole splitting o f 7.12 mm/s. This component may be Au+ or Au3+ in an unusual coordinat ion. Only a small fraction of the gold was found to be metallic in bot h the oxidized and the reduced state.