Y-BA-CU PEROVSKITES AS INTRINSIC ELECTROCHEMICAL REDOX-ELECTRODES

Ternary copper oxides YBa2Cu3O6,5+δ(1), which play an important role in the recent development of high temperature superconductors, were investigated in 1 M NaOH at pellet electrodes. Two cathodic peaks at 650 and 40 mV vs she can be reproducibly measured voltammetrically after anodic saturation of the electrode. The charge ratio is 1 : 3. This is tentatively explained in terms of intrinsic redox processes Cu( 3 2) and Cu( 2 1), respectively. It is only one of three Cu-ions, which can adopt the tervalent state under these conditions (δ=0.5). The positive redox process is reversible within the potential range of this peak, while the negative process degenerates upon cycling, especially, if a negative potential of scan reversal is attained. This is due to the irreversible formation of Cuo. Starting the first scan in negative direction, a diminished positive peak is observed, according to δ=0.2. This corresponds to the value after thermal preparation, which was measured formerly by chemical redox-titration. A simple method for the rapid determination of δ is provided therefore. © 1990.