To date, the highest bulk lithium ion-conducting solid electrolyte is the perovskite (ABO3)-type lithium lanthanum titanate (LLT) Li3 x La(2/3)-x □(1/3) - 2 x TiO3 (0 < x < 0.16) and its related structure materials. The x ≈ 0.1 member exhibits conductivity of 1 × 10-3 S/cm at room temperature with an activation energy of 0.40 eV. The conductivity is comparable to that of commonly used polymer/liquid electrolytes. The ionic conductivity of LLT mainly depends on the size of the A-site ion cation (e.g., La or rare earth, alkali or alkaline earth), lithium and vacancy concentration, and the nature of the B−O bond. For example, replacement of La by other rare earth elements with smaller ionic radii than that of La decreases the lithium ion conductivity, while partial substitution of La by Sr (larger ionic radii than that of La) slightly increases the lithium ion conductivity. The high lithium ion conductivity of LLT is considered to be due to the large concentration of A-site vacancies, and the motion of lithium by a vacancy mechanism through the wide square planar bottleneck between the A sites. It is considered that BO6/TiO6 octahedra tilting facilitate the lithium ion mobility in the perovskite structure. The actual mechanism of lithium ion conduction is not yet clearly understood. In this paper, we review the structural properties, electrical conductivity, and electrochemical characterization of LLT and its related materials.

Inorganic chemistryInorganic chemistry Z 0100 Lithium Lanthanum Titanates: A Review -[155 refs.]. -(STRAMARE, S.; THANGADURAI*, V.; WEPPNER, W.; Chem. Mater. 15 (2003) 21, 3974-3990;

The inclusion compounds (ICs) of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) with several small molecules have been studied, for the first time, by 13C magic angle spinning NMR. The channel-type structure of TPP ICs (about 5 Å wide) provides an aromatic environment to trap some molecules such as benzene, tetrahydrofurane and p-xylene. 13C solid state NMR shows that the high symmetry of the adducts is consistent with an hexagonal crystal cell. The dynamic behaviour of the guest and host molecules has been studied by the measurement of 13C Ti relaxation times and compared with structures containing 10 Å diameter channels. The release of the guest molecules has been followed by differential scanning calorimetry and by solid state NMR. There exist two crystal structures of the guest-free TPP molecule: the former is monoclinic and the latter retains the channel-type structure and hexagonal packing. 13C CP MAS spectra and relaxation times of guest-free TPP structures demonstrate the existence of empty nanotubes stable up to 150 °C. These structures are easily available for uptaking guest molecules by a phenomenon which is quite unusual for molecular architectures. The peak multiplicity of 31P CP MAS spectra reflect the symmetry of the crystal cells together with residual dipolar coupling with 14N.

Abstract. Polycrystalline lithium lanthanum titanates, LixLayTiO 3 (0

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