リチウムイオン伝導性酸化物における高速パーコレーション拡散(第60回日本セラミックス協会学術賞受賞研究総説)

概要

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Lithium ion-conducting perovskite-type oxides, e.g., La_<2/3-x>Li_<3x>TiO_3 show high ionic conductivities as high as 10^<-5>-10^<-3> Scm^<-1> at room temperature. Their high conductivities are attributed to the percolation-controlled diffusion of lithium ions via vacancies in the A-site-deficient perovskites (general formula of perovskite-type oxide: ABO_3). The strong correlation between structure and percolation-controlled diffusion in the perovskites is primarily referred to the arrangement of A-site ions, and the "bottleneck" square-surrounded by four oxygen ions. The bottleneck size, i.e., the repulsion for lithium ions by the electronic clouds of oxygen ions, is dependent on the distortion and tilt of the BO_6 octahedra, which relate to the difference of skeletal ions, A and B cations, i.e., tolerance factor and their chemical characters, and is the predominant factor of the activation energy for ion migration. These findings were confirmed by powder X-ray and neutron structural refinements, composition, temperature and hydrostatic pressure dependences of ionic conductivities, and molecular dynamics simulations.
2006-12-01