Wet chemical passivation of YBa2Cu3O7-x

Wet chemical techniques are described for treatment of YBa2Cu2O7-x surfaces, which result in the formation of native compounds known to have little or no reactivity to water. Suitable native compounds include CuI, BaSO4, CuS, Cu2S, YF3, and the oxalates. Formation of surface layers in which these nonreactive native compounds are major constituents is verified with XPS measurements on YBa2Cu3O7-x films treated with dilute solutions of HI, H2SO4, Na2S, HF, or H2C2O4. No significant changes are observed in the XPS spectra when the sulphide, sulphate, or oxalate films are dipped in water, while the iodide and fluoride films show evidence of reaction with water. X-ray diffraction measurements show that the superconducting phase is absent in the sulphide film, but is unaffected by the oxalate and sulphate treatments. 32 refs.