Water interaction with the superconducting YBa sub 2 Cu sub 3 O sub 7 phase.

We show that the superconducting YBa sub 2 Cu sub 3 O sub 7 phase is highly sensitive to water and water vapor. This is probably due to the presence of nonequilibrium Cu sup (3+) ions in this compound. In particular, the YBa sub 2 Cu sub 3 O sub 7 phase decomposes in water to CuO, Ba(OH) sub 2 and Y sub 2 BaCuO sub 5 and evolves oxygen. Samples with a reduced oxygen content, e.g., YBa sub 2 Cu sub 3 O sub (6.0), also decomposes in an aqueous ambient. The superconductivity of YBa sub 2 Cu sub 3 O sub 7 samples is also 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 then with coatings of metal, glass or plastic.