Oxygen diffusion and phase transformation in YBa2Cu3O7−x

Abstract
Isothermal anneal experiments have been conducted over a wide temperature range from 300 to 900 °C for polycrystalline YBa2 Cu3 O7−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 YBa2 Cu3 O7−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.