Effect of Dopant, Crystal Orientation, and Space Charge Layer on Oxygen Diffusion in Bi₄Ti₃O₁₂ Ceramics

We studied oxygen diffusion in non- and Nb₂O₅-doped Bi₄Ti₃O₁₂ (BIT) ceramics by two-dimensional isotope mapping. In non-doped BIT, the grain boundary acted as a barrier to oxygen diffusion, reflecting the presence of a space charge layer at the grain boundary. In Nb₂O₅-doped BIT, a textured morphology was found by bulk and grain-boundary diffusion of oxygen. Diffusion coefficients were determined from the individual grains and grain boundaries. The difference in diffusion paths resulted from the decrease in oxygen-defect concentration owing to the addition of Nb₂O₅. The bulk-diffusion coefficient along the ab-plane was about one order of magnitude larger than that in the direction of the c-axis. The grain-boundary-diffusion coefficients varied by about two orders of magnitude. The bulk and grain-boundary diffusion of oxygen depended significantly on the crystal orientation.