A substrate for supporting a ceramic superconductor comprises a metallic base member precoated with an yttrium oxide, rare earth oxide, or zirconium oxide layer and having a constituent oxide former which establishes an oxide layer with the yttrium oxide, rear earth oxide, or zirconium oxide on the surface of the substrate. A layer of ceramic superconducting material covers the substrate with the oxide layer between the metallic base member and the ceramic superconductor layer to inhibit the interdiffusion of respective constituent elements between the metallic base member and the ceramic layer. For applications requiring the transmission of electrical current through the ceramic layer over relatively extensive distances, the substrate can be formed as a wire or ribbon.