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MM: Fachverband Metall- und Materialphysik

MM 27: Transport I - Materials/Methods

MM 27.4: Talk

Tuesday, April 1, 2014, 12:30–12:45, IFW B

Conductivity and Dielectric Properties of Li_xNa_2−xTi₆O₁₃ (x = 0 ... 2) — •Kai Volgmann and Paul Heitjans — Leibniz Universität Hannover, Inst. f. Phys. Chemie u. Elektrochemie, Callinstraße 3 - 3a, D-30167 Hannover

Titanate systems attract much attention as anode material for secondary Li ion batteries due to advantages compared to graphite. TiO₂ is a prominent example within the system Li₂O - TiO₂. In the present work, Li_xNa_2−xTi₆O₁₃ (space group C2/m) has been chosen as a model system because of its channel-like crystal structure. The alkali atoms are solely located inside the channels. The samples with different Li/Na ratios were characterized by powder x-ray diffraction and inductively coupled plasma optical emission spectroscopy (ICP-OES). Impedance spectroscopy measurements were performed over a wide temperature range (200-1000 K). Thin films of graphite or Pt were used as electrodes. The frequency dependent conductivity data yielded activation energies E_A which partly depend on the Li/Na ratio. Whereas E_A values calculated from the DC plateau are essentially independent of x, the AC contribution has a maximum E_A value for x = 0.33. Cole-Cole plots of the complex impedance show a depressed semicircle. Thus no separation of bulk and grain boundary contributions is visible. Plotting the complex modulus vs. frequency shows different relaxation modes corresponding to different bulk processes. Comparison of the various representations gives information on the diffusivity of the alkali ions on macroscopic and microscopic scales.