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

在这个项目中，我们研究了金属间化合物前驱体的氧化作为一种制备14族元素亚稳态金属间化合物相和同素异形体的方法。在第一个供资期间，进一步发展了实验方法，并提供了新类型的化合物。在下一个供资期间，我们计划重点研究以下主题：根据我们先前获得的结果，将调查第13族元素的氧化。不同的氧化方法将适用于新的体系，如碳化物或含有稀土元素的前驱体。通过氧化制备的硅和锗的同素异形体将被研究关于金属和非金属客体成分的吸收。通过这种方式，我们计划获得一类新的亚稳态笼状化合物。到目前为止，氧化产物的物理性质测量一直受到非晶态和纳米晶副产物的存在以及晶界绝缘的阻碍。对氧化产物的详细研究将通过电子显微镜进行，实验工作将通过数值模拟进行支持。在计划的理论研究的第一部分，将模拟金属间化合物前体的氧化降解，以了解重要但在实验上难以获得的反应机理细节。因此，我们将采用上一次筹资期间开发的方法。在第二部分中，我们将用从头算方法探索亚稳态相。应用分子动力学，我们将寻找碳、硅和锗的新同素异形体。将确定合适的前体，并建议将其作为实验的起始材料。根据关于镓的新的实验结果，将详细研究元素Ga的相图，以寻找合成新的亚稳态Ga同素异形体的可能性。

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.