Electrochemical oxidation of Y-Ba-Cu-O high-Tc superconductors

The electrochemical oxidation of YBa2CU3O7-delta high-T-c, superconductor (both films and ceramics) in a KNO3-NaNO3 melt has been studied. Anodic polarization of nonsuperconducting oxygen-deficient films of about 2000 Angstrom thick at T = 360 degrees C, i = 50 mA cm(-2) for t approximate to 40 s leads to the appearance of superconductivity of the sample with T-c = 89 K. The estimation of temperature dependence of the oxidation efficiency is made and the optimum oxidation temperature it; found to be 350 degrees C. The efficiency of oxidation falls and anodic dissolution of the sample begins as the temperature decreases. For electrochemical oxidation in the melt at T greater than or equal to 350 degrees C, the oxidation efficiency is equal to similar to 1% for YBa2CU3O7-delta films and almost 100% for ceramics; This fact indicates an important role of the sample morphology and grain-boundary ionic transport in the process of electrochemical oxidation. (C) 1998 Elsevier Science Ltd. All rights reserved.