Investigations on formation mechanisms and preparation of metastable allotropes and compounds of group 13 and 14 elements by oxidation of intermetallic phases

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In this project, we have investigated the oxidation of intermetallic precursors as a method for the preparation of metastable intermetallic phases and allotropes of group 14 elements. In the first funding period, the experimental methods were further developed and new types of compounds were made accessible. In the next funding period we plan to focus on the following topics: Based on the results which we have previously obtained the oxidation of group 13 elements will be investigated. Different oxidation methods will be adapted to new systems like carbides or precursors containing rare earth elements. Allotropes of Si and Ge prepared by oxidation will be investigated with respect to an uptake of metallic and nonmetallic guest components. In this way we plan to access a new class of metastable clathrates. So far, the physical property measurements of oxidation products have been hindered by the presence of amorphous and nanocrystalline byproducts and by insulating grain boundaries. Detailed investigations on the oxidation products will be performed by electron microscopy.The experimental works will be supported by numerical simulations. In the first part of the planned theoretical studies, the oxidative degradation of intermetallic precursors will be simulated in order to understand important but experimentally hardly accessible details of the reaction mechanisms. Therefor we will apply the method which was developed in the last funding period. In the second part, we will explore metastable phases by ab-initio methods. Applying molecular dynamics we will seek for new allotropes of carbon, silicon and germanium. Suitable precursors will be identified and suggested as starting materials for experiments. With respect to the new experimental results on gallides, the phase diagram of elemental Ga will be investigated in detail to find possibilities for the synthesis of a new metastable Ga allotrope.