Molecular Level Synthesis of High Entropy Oxides and Sulfides from Metal Alkoxides and Thiolates

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This dissertation describes the synthesis, processing, and fundamental insights into chemical processing of high-entropy oxides (HEOs) and high-entropy sulfides (HESs) using metal alkoxides and thiolates. One of the aims was to systematically investigate how different precursor chemistries influence the formation of entropy-stabilized phases. The central focus of the dissertation is based on the multi-source precursor-based synthesis of high entropy materials. Part of this is the polymer-assisted electrospinning of high entropy oxide fibers using PVP as viscous matrix, obtaining continuous (MnFeNiCoZn)3O4 nanofibers. A systematic investigation of alkoxide-based high-entropy oxides allowed control over hydrolysis and condensation reactions to precisely achieve different M:O stoichiometries, including MO2, M2O3, and mixed-valence systems of the type (MIV3MIIIMV)O2. This precursor-based approach allowed clear correlations between precursor reactivity, oxidation state compatibility, and phase formation. Particularly noteworthy is the successful stabilization of mixed-valent HEOs that go beyond classical equimolar systems. Within this work, even HEO thin films were successfully prepared by employing a mixture of molecular alkoxides in a commercial vaporizer. This technical system enables the controlled injection of multi-metallic precursor solutions and bridges the gap between solution-based chemistry and plasma-assisted thin film deposition. Finally, the precursor concept for high entropy materials was extended to chalcogenides through the synthesis of tetravalent metal thiolates and their use in thiol-based sol-gel routes to obtain high entropy sulfides. The work reported in this dissertation illustrates that high-entropy materials are not formed by purely thermodynamic driven phenomenon and precursor chemistry, reaction kinetics, and process control are decisive factors for their successful synthesis

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Ziyaad Aytuna

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Precursor Chemistry Materials Chemistry Mulitmetallic Ceramics

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