Passivation of high temperature superconductors

This patent describes a method of passivating the surface of a metal cuprate high temperature superconductor material. It comprises: reacting the native metals on the surface of the superconductor material with an aqueous solution of a reagent that does not degrade the superconducting properties of the material, the reagent being reactive with the native metal ions and being selected form compounds of the formula: M3X where M3 is selected from H, ammonium and Group I metal ions, and X is an anion selected from halide, sulfide, sulfate and oxalate; and forming a passivating layer on the surface of the material, the layer consisting essentially of a salt of the anion of the reagent and at least one of the native metal ions, the layer having a solubility in water of no more than 10-3M