Diffusion Path of Oxide Ions in La0.64(Ti0.92Nb0.08)O3

Quantum Beam Center, National Institute for Materials Science* Department of Materials Science and Engineering, Tokyo Institute of Technology, Japan**
○Roushown Ali* Masatomo Yashima** Fujio Izumi*

Solid oxides that exhibit high ionic conductivity have received special attention in recent years owing to their potential applications in both batteries and fuel cells. To develop and exploit better oxide-ion conductors, we need to understand the mechanism of diffusion of mobile ions at high temperature where the materials work efficiently. In this study, we have studied the crystal structure and pathway of oxide-ion conduction in an A-site deficient perovskite-type oxide, La0.64(Ti0.92Nb0.08)O3, at high temperature by neutron powder diffraction.
Densities of coherent-scattering lengths in La0.64(Ti0.92Nb0.08)O3 (P4/mmm) have been determined by whole-pattern fitting based on the maximum-entropy method (MPF) from neutron powder diffraction data measured at 496 ゚C, 1008 ゚C and 1358 ゚C. The combination of RIETAN-2000 and PRIMA were used for MPF. Oxide ions located at a 4i site are disordered along <100> and <010> directions. These oxide ions tend to be localized near the 4i site with decreasing temperature while they spread over a wide space near the (001) plane. The diffusion path of oxide ions was clearly visualized in a density map obtained for the (001) plane from the diffraction data measured at 1358 ゚C. The equi-density level of the position intermediate between the oxygen atoms was 0.1 fm Å-3 and 0.05 fm Å-3 at 1358 ゚C and 1008 ゚C, respectively, whereas it was practically null at 496 ゚C. The appreciable increases in nuclear densities between the oxide ions with increasing temperature shows that oxide ions responsible for ionic conduction migrate near lines connecting these oxide ions.