COMPARATIVE-STUDY OF OXYGEN DIFFUSION IN RARE-EARTH REBA2CU3O7-DELTA SINGLE-CRYSTALS (RE = Y, ER, DY) WITH DIFFERENT IMPURITY LEVELS

We report on measurements of the chemical diffusion coefficients of ra re earth cuprate single crystals REBa2Cu3O7-delta (RE = Y, Er, Dy) gro wn in crucibles made of Y2O3-stabilized ZrO2 and BaZrO3. The diffusion coefficients have been determined by in situ measurement of the elect rical conductivity using a four point method during the oxygenation at various oxygen partial pressures and in the temperature range of 390 degrees C-550 degrees C. In this range the diffusion coefficient was d etermined between 3.7 X 10(-9) cm(2)/s and 6.6 X 10(-8) cm(2)/s indepe ndent of the rare earth atom or of the different impurity levels. For all crystals we show that the in- and out-diffusion process can be des cribed with the same time constant at each annealing temperature. With in the accuracy of +/-5% we measure for both processes the same value for the diffusion coefficient. The temperature dependence of the diffu sion coefficient obeys an Arrhenius-law for all crystals, proving that the oxygen diffusion in the rare earth RE 123 superconductors is a pu rely thermally activated process. The values for the activation energy show a scattering up to 30% and vary from 0.76 to 1.09 eV. There is n either a dependence of the activation energy on the central rare earth atom nor on different impurity levels. (C) 1998 Elsevier Science B.V. All rights reserved.