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

Abstract The electrochemical oxidation of YBa 2 Cu 3 O 7- δ high- T c superconductor (both films and ceramics) in a KNO 3 –NaNO 3 melt has been studied. Anodic polarization of nonsuperconducting oxygen-deficient films of about 2000 Athick at  T =360°C, i =50 mA cm −2 for t ≈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 is found to be 350°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 ≥350°C, the oxidation efficiency is equal to ∼1% for YBa 2 Cu 3 O 7- δ 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.