Diffusion pathway of mobile ions and crystal structure of ionic and mixed conductors - A brief review

A brief review on the field of Solid State Ionics, including the diffusion pathway of mobile ions, crystal structure and materials, is presented. In the fluorite-structured ionic conductors such as ceria solid solution Ce0.93Y0.07O1.96, bismuth oxide solid solution δ-Bi1.4Yb0.6O3 and copper iodide CuI, a similar curved diffusion pathway along the <100> directions is observed. In the ionic and mixed conductors with the cubic ABO3 perovskite-type structure such as lanthanum gallate and lanthanum cobaltite solid solutions, the mobile ions diffuse along a curved line keeping the interatomic distance between the B cation and O2- anion to some degree. The structure and diffusion path of double-perovskite-type La0.64Ti0.92Nb0.08O2.99, K2NiF4-type (Pr0.9La0.1)2(Ni0.74Cu0.21Ga0.05)O4+δ , and apatite-type La9.69(Si5.70Mg0.30)O26.24 are described. The diffusion paths of Li+ ions in La0.62Li0.16TiO3 and Li0.6FePO4 are two- and one-dimensional, respectively.