Effect of pressure on transport properties of granular lithium ion conductors

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A central issue of TP is the synthesis of new amorphous Li-bearing solids and the investigation of the change in lithium mobility upon high pressure - high temperature treatment. A primary goal of the project is to determine experimentally the relationships between transport properties and the following parameters: - composition and structure type - state of ordering - degree of compaction - local environment of lithium In the first period we have focussed on the synthesis, compaction and characterization of amorphous compounds in the system Li2O-Al2O3-SiO2. Lithium mobility was determined using impedance spectroscopy and NMR. Following this approach we want to study the influence of composition structural state and particle size on the transport of lithium for selected systems in situ during pressure/temperature treatment of amorphous powders. We choose two model systems representing more ionic (e.g., LiTaO3 und LiNbO3) and more covalent materials (e.g., LiFePO4 or LiMgPO4, the latter one has the advantage that Mg has a single oxidation state), respectively. The aim of the project is to separate effects of volume and grain boundary diffusion on Li-transport in granular single phase systems and to investigate the change of theses transport properties during compaction. For doing so, we want to apply the new piston cylinder apparatus which was developed during the first period of the project. The method allows direct measurement of impedance spectra and volume changes during compaction in function of temperature and pressure. Using an atmosphere with controlled humidity and oxygen partial pressure, the powders can be pre-conditioned at run temperature before starting compression. We expect in particular that H2O has major impact on compaction kinetics and in turn on lithium mobility. Microanalytical and spectroscopic methods will give insights to structural and topological modifications upon compaction. NMR measurements and, if possible, mechanical relaxation spectroscopy will provide information about lithium mobility in starting materials and post-experimental samples.