Isotopic Effects, Jump Correlation and Diffusion Paths in Li-containing Oxide Glasses

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The subproject focuses on systematic investigation of the chemical diffusion and self-diffusion of lithium in amorphous and crystal oxide phases. Diffusion couple experiments will be used to study lithium diffusion in chemically homogenous materials and in systems with a chemical potential gradient. The elemental and isotopic diffusion profiles will be measured using mass spectroscopy coupled with laser ablation (both MC-ICP-MS and Sektorfeld-MS) and then mathematically processed using diffusion equations. Li-migration mechanisms are insufficiently understood in oxide glasses and thus such materials stand in the core of this study. The comparison between single crystals and glasses, as well as other structural modifications yields insight into the impact of short- and long-range order on Li-diffusion. The results of our studies of silicates and aluminosilicates in the first project period shall be expanded by incorporating investigations on other oxide systems with the high content of covalent bonding, namely borates and phosphates. Structural variations in glasses can be induced by varying the cooling rate. Lower densities will be achieved through rapid quenching at ambient pressure, e.g. using a Roller-Quenching technique, while the higher densities can be achieved by slow cooling at high pressures. The results obtained by impedance spectroscopy combined with the diffusion experiments allow precisely characterizing the correlation factors affecting Li-mobility. The correlation coefficient in solid state materials is determined by defects and by the potential landscape. The interpretation of experimentally obtained correlation coefficients in amorphous systems is challenging. In this respect theoretical modelling will help in identifying the dominant mechanisms of Li-diffusion. Solid state quantum chemical and classical calculations will be performed on simple model systems with a periodical supercell representing structural features of glasses. One of the principal goals of this project is to develop theories to predict the diffusion properties in function of the composition and the local structure of the materials. Firstly, models will be to describe the diffusion behaviour in systems studied in the first project period (silicates and aluminosilicates). Afterwards, the modelling concept will be applied to other systems to identify fundamental constraints on Li-mobility. Subsequently, the modelling concepts will be experimentally tested to elaborate possibilities for prediction of diffusion behaviour of Li-bearing glasses.