Oxygen tracer diffusion in the YBa(2)Cu(3)Oy superconductor

The oxygen diffusion coefficient of YBa2Cu3Oy (YBCO) single crystals was de termined by secondary ion mass spectrometry in a wide temperature range fro m 628 to 1073 K. It was found that the slope of the Arrhenius plot of the d iffusion coefficient changes at the transition temperature from the orthorh ombic to the tetragonal phase (TP). The activation energies of oxygen in th e 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 coeff icients in the ab plane are larger than that in the c axis direction by mor e than three orders of magnitude. At higher temperatures of the TP, the slo pe of the Arrhenius plot in the c axis direction becomes larger and the dif fusion coefficient of the c axis becomes closer to that of the ab plane tow ards the incongruent melting point of YBCO compounds. (C) 2001 Elsevier Sci ence B.V. All rights reserved.