Room-temperature electrochemical reduction of YBa2Cu3O7 –x. Solid-state and solution chemical results

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Abstract
The oxygen content of polycrystalline samples of YBa2Cu3O7 –x can be reduced quantitatively, in a controlled fashion, by electrochemical techniques at room temperature in propylene carbonate. Upon reduction, the propylene carbonate undergoes an unusual reaction at the YBa2Cu3O7 –x cathode to produce propanal, apparently because of the production of an active oxygen species on the surface. The reduced materials have been characterized by X-ray powder diffraction, electrical resistivity and magnetic susceptibility. The large-grained, reduced pellets are found to be inhomogeneous with respect to x. The reduced materials exhibit a broadened transition to the superconducting state. This effect is ascribed to the formation of metastable phases formed during reduction. After a low-temperature anneal, 80, 60 and 20 K transition temperatures are observed. These results indicate that Tc is a continuous function of oxygen content, but a discontinuous function of oxygen ordering.