Wet chemical techniques for passivation of YBa2Cu3O7−x

Wet chemical techniques are described for treatment of YBa2Cu3O7−x surfaces, resulting in the formation of native compounds with little or no reactivity to water. Promising native compounds include CuI, BaSO4, CuS, Cu2S, and the oxalates, all of which are either insoluble or have very low solubility in water. Treatment with dilute HI results in the formation of anative iodide film which is 80–90% CuI with small amounts of YI3 and BaI2. Treatment with dilute H2SO4 results in the formation of a film which is 95% BaSO4 and 5% Y2(SO4)3. Cu2S is formed on the surface with a dilute Na2S solution. An oxalate film with equal amounts of Y2(C2O4)3 and BaC2O4 results from treatment with dilute oxalic acid. X-ray photoelectron spectra show no significant changes when the sulfide, sulfate, or oxalate films are dipped in water, while the iodide film shows evidence of Cu(OH)2 formation.