Zur chemischen Bindung in schichtartigen Chalkogeniden

  • On chemical bonding in layered chalcogenides

Konze, Philipp Maximilian; Dronskowski, Richard (Thesis advisor); Wuttig, Matthias (Thesis advisor)

Aachen (2019)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2019

Abstract

Within the scope of this thesis, different chalcogenides with layered structures were considered and investigated for their electronic structure, stability and chemical bonding. Furthermore, the nature and strength of the interactions between the layers in such compounds has been characterized to better understand the relationship between structures and properties. First, a detailed introduction to the orbital-based bonding analysis of solids has been provided and, based on this, previous results of the bonding analysis of phase change materials are summarized and an antibonding region below the Fermi level was identified as a possible fingerprint of such materials. Furthermore, it was shown how the strength of various bonds in complex solid-state structures can be evaluated by means of ab initio methods and how the bonding analysis helps to understand the unusual structures of certain chalcogenides. In the results section, the layered structure of Ge₄Se₃Te was introduced. The strength of the Ch-Ch contacts between the layers and Ge-Ge contacts within the layers was investigated by means of various thought experiments. Subsequently, the transition from the α-GeTe structure to the structure of Ge₄Se₃Te was investigated by chemical bonding analysis in the context of the crystal orbital Hamiltonian population analysis. Furthermore, the structural diversity of In₂Se₃ was examined. Of the six stable phases at ambient pressure, there are three stable at room temperature and three at elevated temperatures. The experimental findings on the dynamic stability of In₂Se₃ could be confirmed by the calculation of the phonon dispersion and the different coordination polyhedra of the structures were then investigated in the context of chemical bonding and Mulliken charge analysis. In the last chapter of this work, the structure-property relationships of different chalcogenides with layered structures were investigated, and the strength of inter-layer interactions was related to the properties of hypothetical structures with two-dimensional defects. In summary, the structures of diverse layered chalcogenides were investigated in this work. Many functional chalcogenides, which are being investigated for applications as data storage materials, thermoelectrics, solar cells, and more, contain unusual structural elements that have been investigated by orbital-based bonding analysis.

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