Diffusion path of oxide ions in an oxide ion conductor La0.64(Ti0.92Nb0.08)O2.99 with a double perovskite-type structure

Densities of coherent-scattering lengths in an oxide ion conductor La-0.64(Ti0.92Nb0.08)O-2.99 with a double perovskite-type structure (space group P4/mmm) are determined using neutron powder diffraction data by a whole-pattern fitting approach based on the maximum-entropy method. At temperatures of 496 degrees C, 1008 degrees C, and 1358 degrees C, oxide ions at the 4i site (1/2, 0, z) are largely distributed along the < 101 > directions near the stable positions. The spatial distribution of these oxide ions becomes larger with an increase of temperature. These oxide ions migrate to nearest-neighbor 4i sites along the [100] and [010] directions near the (004) planes at 1008 degrees C and 1358 degrees C, corresponding to the spatial dispersion of oxide ions from close to the 4i site onto a wide area of the (004) plane with increasing temperature. The two dimensionality of diffusion paths is attributable to the layered structure of the double perovskite-type La-0.64(Ti0.92Nb0.08)O-2.99 compound.