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MM: Fachverband Metall- und Materialphysik

MM 30: Poster Session II

MM 30.23: Poster

Dienstag, 17. März 2020, 18:15–20:00, P4

Phase transformation in Li4+xTi5O12 probed optically — •Yug Joshi, Robert Lawitzki, and Guido Schmitz — Chair of Materials Physics, Institute of Materials Science, University of Stuttgart, Stuttgart, Germany

The mechanism and the kinetics of the phase transformation from spinel structured Li4Ti5O12 to rock-salt type Li7Ti5O12 is studied by utilizing the electrochromic properties of the material. Thin films of Li4Ti5O12 are deposited on platinum-coated substrates using rf-ion beam sputtering. In-situ and ex-situ optical spectroscopy (in reflectance geometry) is performed along with electrochemical characterization. In-situ measurements demonstrate the reversible electrochromic behavior of the deposited thin films and the effect of the change of lithium content on the reflectance spectrum. The kinetics of the phase transformation is examined by probing the lateral diffusion lengths of lithium, optically revealed by the drastic blue color of the lithium-rich rock salt phase. Ex-situ measurements quantify the optical constants of the thin films for different charge states, by modeling the reflectance spectrum with a Clausius-Mossotti relation. The concentration dependence of the derived dielectric constants points out a fast lithium ion transport through the grain boundaries, thereby segregating a conductive lithium-rich phase at the grain boundaries. This is further confirmed by the change in the lateral diffusion lengths (reveled optically) with the varying grain sizes.