In-situ resistivity measurements during the oxygenation of YBa 2Cu 3O 7−δ and Gd 0.8Y 0.2Ba 2Cu 3O 7−δ single crystals

Abstract

We report on measurements of the electrical resistivity during the oxygenation of single crystals of YBa 2Cu 3O 7−δ and Gd 0.8Y 0.2Ba 2Cu 3O 7−δ. Real four-point probe resistivity measurements were performed between room temperature and 650°C in pure oxygen atmosphere. The crystals were kept at each temperature as long as they reached an equilibrium state with no further changes in the resistivity. From the R( t) curves we were able to calculate the chemical diffusion coefficient for various temperatures between 380 and 600°C. In contrast to some literature the diffusion coefficients for oxygen in- and out diffusion were found to have the same value. The values of the diffusion coefficient for the different temperatures obey an Arrhenius law, thus allowing a determination to be made of the activation energy for oxygen diffusion. For Gd 0.8Y 0.2Ba 2Cu 3O 7−δ crystals D 0 was determined to be 4.94 × 10 −5 cm 2/s. The activation energy ΔE was found to be 0.52 eV. For YBa 2Cu 3O 7−δ crystals the activation energy ΔE was determined to be about 0.8 eV. The very low values compared to the results of other authors, which we obtained for the diffusion coefficient of oxygen in our crystals are in good agreement with the small impurity content we found in these crystals and with the observed long time, which is required for a full oxygenation.