Relationship Between Crystal Structure and Li + -Conductivity in La 0.5 Li 0.5 TiO 3 Perovskite

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RELATIONSHIP BETWEEN CRYSTAL STRUCTURE AND Li+-CONDUCTIVITY IN La0•LioTiO 3 PEROVSKITE J.A. Alonso*. J. Ibarra, M.A. Paris, J. Sanz*, J. Santamaria**, C. Le6n**, A. Vdrezý, M.T. FermAndezj, *Inst. Ciencia de Materiales de Madrid, CSIC, Cantoblanco, E-28049 Madrid. Spain,.** F. C. Fisicas, Univ. Compl. Madrid, E-28040 Madrid. Spain.tE.P.S., Univ. Carlos III, E-28911 Legands. Spain.jInst. Laue-Langevin, BP 156. F-38045 Grenoble Cedex 9. France ABSTRACT For the first time Li+ cations have been localized within the perovskite structure of the fast Liconductor La0 5Li 05TiO 3 from neutron powder diffraction data. Li cations are fourfold oxygen coordinated, located in the middle of the almost square windows determined by every four TiO 6 octahedra, far away from the 12-fold coordinated La vacancy sites that, nevertheless, take part of the path for Li motion across the solid. The large multiplicity of the sites where Li reside (1/6 occupied) accounts for the huge ionic conductivity of this promising Li-conducting material. INTRODUCTION Interest in lithium ion-conducting solids is increasing considerably in the last years because of their potential application in lithium rechargeable batteries. In particular, ionic conductivity of LiLa 2/3 ._TiO3 perovskites is one of the highest reported values in lithium crystalline conductors [1,2] (= 10-3 a'cm' at T= 300K), making these compounds good candidates for solid electrolytes in lithium batteries. The conductivities in the Pr and Nd perovskites are 2 and 3 orders of magnitude lower than their La analogues [2]. Perovskite structure (general formula ABO 3) can be regarded as a 3-dimensional framework built up by vertex-sharing B0 6 octahedra with a large A cation in the 12-coordinated cavities of the framework. If the radius of A cations is too small, the void is reduced in size by tilting of the B0 6 octahedra. The effect of tilting, widely extended, is a predominant feature which determines the overall space-group symmetry of a particular perovskite. In the solid solution LiLa3_. 3 TiO3 (0

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