The oxygen in- and out-diffusion behavior in melt-textured YBCO measured by thermogravimetry

Abstract

The chemical oxygen in- and out-diffusion in melt-textured YBa2Cu 3O7-δ（YBCO）is investigated by thermogravimetry. The weight relaxations resulting from the sudden change of temperature at a fixed oxygen partial pressure of 033×１０5Pa are recorded. By fitting the isothermal curves, the chemical diffusion coefficients at 375—600℃ are determined. It is found that the resultant numerical values for melt-textured YBCO are larger than that of crushed single crystal YBCO obtained in our previous study by about 50%, whereas all of them are of the order of 10-10cm2s-1 . The activation energies for both samples are estimated as ～1eV. It is believed that those values represent the nature of the lattice diffusion. The oxygen diffusion in me lt-textured-grown-YBCO is attributed to the YBCO matrix and the micro-cracks are responsible for the huge diffusion coefficients. Moreover, the same kinetics o f in- and out-diffusion is confirmed to be intrinsic, and it suggests that the d ifferent in- and out-diffusion coefficients measured in other works are controll ed by the large concentration gradient and the shell effect.