Synthesis of Lithium Silicides, Germanides and Stannides with Ion Exchange Materials

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For two reasons binary lithium compounds of the elements Si, Ge and Sn are interesting materials for renewable energy sources, i. e. they can serve as anode materials and as precursor materials for semiconducting Si and Ge allotropes with interesting optoelectronical properties. In preliminary experimental and theoretical studies the applicant has shown that nine-atom clusters E9 can be oxidatively coupled in solution, and that new metastable allotropes of the elements can be obtained from lithium-containing precursors. The stability of allotropes of the elements which contain nine-atom clusters has also been indicated by theoretical investigations. Materials with direct band gaps significantly increase the efficiency of solar cells. Within this project the class of lithium-containing Zintl phases with nine-atom clusters E9, which are not directly accessible so far, are to be developed systematically, starting from the heavier, better-accessible homologues by using ion exchange techniques. The successful synthesis of Li4Sn9 from K4Sn9 via this novel synthetic route for this kind of compounds by ion exchange in liquid ammonia in the course of preliminary studies serves as a proof of principle. In the following, the lithium in the resulting products should be removed oxidatively by using established methods developed in our laboratory for the delithiation of other lithium-containing compounds (e. g. Li7Ge12). This should in best-case lead to new modifications of the elements which still contain the nine atom clusters and possess direct band gaps.