Crystal Structure and Ion-Diffusion Pathway of Inorganic Materials through Neutron Diffraction

Abstract

The present brief review describes the application of neutron powder diffractometry and maximum-entropy method to the studies of crystal structure and diffusional pathways of mobile ions in ionic conducting ceramic materials. La_0.62Li_0.16TiO₃ and Li_0.6FePO₄ exhibit two- and one-dimensional networks of Li cation diffusional pathways, respectively. In the fluorite-structured ionic conductors such as ceria solid solution Ce_0.93Y_0.07O_1.96, bismuth oxide solid solution δ-Bi_1.4Yb_0.6O₃ and copper iodide CuI, a similar curved diffusion pathway along the ‹100› directions is observed. In the cubic ABO₃ perovskite-type ionic conductor, lanthanum gallate solid solution, the mobile ions diffuse along a curved line keeping the interatomic distance between the B cation and O^2- anion. We have experimentally confirmed that the anisotropic thermal motions of the apex O2 atom and the interstitial O3 atoms are essential for the high oxygen permeability of the K₂NiF₄-type mixed conductor. Diffusion paths of proton are visualized along c axis in hexagonal hydroxyapatite.