Stabilization of Ba₂YCu₃O7-δ by Surface Coating with Plasma Polymerized Fluorocarbon Film

High- T c superconducting Ba 2 YCu 3 O 7-δ pellets were coated with polyfluorocarbon thin films prepared by plasma polymerization of tetrafluoroethene (C 2 F 4 ). The polymer-coated Ba 2 YCu 3 O 7-δ preserved its high- T c superconductivity even after it had been kept standing in water at 60°C, whereas the superconductivity of noncoated pellets was completely destroyed under the same condition. The high hydrophobicity of the film originated from high fluorine content is considered to be primarily responsible for the protection of the superconductor from chemical deterioration by preventing the hydrolysis at the surface.