REACTION OF THE OXYGEN-DEFICIENT YBA2CU3O6 PHASE WITH WATER

The oxygen deficient high-T(c) material, YBa2Cu3O6, decomposes rapidly when in the presence of water solution or water vapor. Accordingly, upon reaction with water, it decomposes into Ba(OH)2, Cu2O, CuO, a metastable ''Y2BaCuO5'' phase and a series of unidentified amorphous compounds. Although the majority of the decomposition products are insoluble in water, Ba(OH)2 leaches away into solution where it subsequently reacts with atmospheric CO2 to form sparingly soluble BaCO3 Crystals. Interestingly, the ''Y2BaCuO5'' phase forms only in the initial stages of corrosion and disappears after long water exposure times. On the other hand, authentic Y2BaCuO5 Samples are very stable in the presence of water. Thus, the chemical reactivity of the ''Y2BaCuO5'' phase generated via decomposition of the high-T(c) material is different from that of the authentic phase. In addition, comparisons of the relative reactivity of YBa2Cu3O7 and YBa2Cu3O6 samples reveal that the oxygen deficient material is more reactive than the fully oxygenated compound. This unusual reactivity trend suggests that factors other than copper formal valence dominate the chemical reactivity of the high-T(c) phase.