Oxygen tracer diffusion in the YBa2Cu3Oy superconductor

The oxygen diffusion coefficient of YBa2Cu3Oy (YBCO) single crystals was determined by secondary ion mass spectrometry in a wide temperature range from 628 to 1073 K. It was found that the slope of the Arrhenius plot of the diffusion coefficient changes at the transition temperature from the orthorhombic to the tetragonal phase (TP). The activation energies of oxygen in the TP and the orthorhombic phase (OP) are 89.1 +/- 1.4 and 114.6 +/- 1 kJmol(-1) in the ab plane, and 284 +/- 2.8 and 126.9 +/- 0.5 kJmol(-1) in the c axis direction, respectively. In the OF, the activation energies in the ab plane and the c axis direction are almost the same, but the diffusion coefficients in the ab plane are larger than that in the c axis direction by more than three orders of magnitude. At higher temperatures of the TP, the slope of the Arrhenius plot in the c axis direction becomes larger and the diffusion coefficient of the c axis becomes closer to that of the ab plane towards the incongruent melting point of YBCO compounds. (C) 2001 Elsevier Science B.V. All rights reserved.