Oxygen diffusion and phase transformation in YBa2Cu3O7-x

Isothermal anneal experiments have been conducted over a wide temperature range from 300 to 900 degree C for polycrystalline YBa2Cu3O7-x samples in air. The phase transformation and oxygen contents of the annealed samples were studied and determined by x-ray diffraction and iodine titration. Oxygen diffusion coefficients at different temperatures were determined by a novel technique based on direct observation of the oxygen diffusion fronts by polarized light microscopy. The activation energy for the diffusion of oxygen in YBa2Cu3O7-x was obtained by an Arrhenius plot of the diffusion coefficients at different temperatures. The tetragonal-to-orthorhombic phase transformation controlled by oxygen diffusion is discussed