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，我们研究了金属间前体的氧化作为制备亚稳金属间相和14族元素的同素异形体的方法。在第一个资助期内，进一步发展了实验方法，并获得了新型化合物。在下一个资助期内，我们计划重点关注以下主题：基于我们之前获得的结果，我们将研究第13族元素的氧化。不同的氧化方法将适应新的体系，如碳化物或含有稀土元素的前体。通过氧化制备的Si和Ge的同素异形体将研究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包合物。到目前为止，氧化产物的物理性质测量受到非晶和纳米晶副产物的存在以及绝缘晶界的阻碍。对氧化产物的详细研究将通过电子显微镜进行。实验工作将得到数值模拟的支持。在计划的理论研究的第一部分中，将模拟金属间前体的氧化降解，以了解反应机制的重要但实验上难以获得的细节。因此，我们将采用在上一个资助期间开发的方法。在第二部分，我们将用从头算方法探讨亚稳相。应用分子动力学，我们将寻找碳、硅和锗的新同素异形体。将确定并建议合适的前体作为实验的起始材料。结合新的实验结果，我们将对元素镓的相图进行详细的研究，以寻找合成新的亚稳态镓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.