Water interaction with the superconducting YBa2Cu3O7 phase

We show that the superconducting YBa2Cu3O7 phase is highly sensitive to water and water vapor. This is probably due to the presence of nonequilibrium Cu3+ ions in this compound. In particular, the YBa2Cu3O7 phase decomposes in water to CuO, Ba(OH)2 and Y2BaCuO5 and evolves oxygen. Samples with a reduced oxygen content, e.g., YBa2Cu3O6.0, also decompose in an aqueous ambient. The superconductivity of YBa2Cu3O7 samples is greatly degraded by the interaction with water and humid air. This effect should not preclude practical application of these materials since it should be possible to protect them with coatings of metal, glass, or plastic.