Application of the van der Pauw method to conductivity relaxation experiments on YBa2Cu3O6+δ

The van der Pauw method has been applied to conductivity relaxation experiments on YBa2CU3O6+delta at 600 degreesC in order to determine the chemical diffusion coefficient as a function of the oxygen partial pressure in the surrounding atmosphere ( 10(0) > p(O2) /bar > 10(-3)). It is shown that the van der Pauw technique is suitable for monitoring the conductivity relaxation when the oxygen diffusion is perpendicular to the direct current flowing through the sample in accordance with the van der Pauw geometry using thin tablets as samples. The oxygen partial pressure is changed stepwise (generally Delta logp(O2) less than or equal to 0.5) by employing appropriate gas mixtures as well as an electrochemical oxygen pump device. An evaluation formula is given for the determination of the chemical diffusion coefficient neglecting slow surface processes. In addition, the electronic conductivity of YBa2CU3O6-delta has been measured at 600 degreesC as a function of oxygen partial pressure of the ambient atmosphere (10(0) > p(O2)/bar > 10(-5)) by means of the van der Pauw method applying the same experimental set-up. Typical values of the chemical diffusion coefficient are in the range of 10(-6)cm(2 .) s(-1); the results of the conductivity measurements are interpreted in terms of an appropriate defect model.