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Rare-Earth-Containing Chalcohalides and Intermetallics
- Author / Creator
- Mumbaraddi, Dundappa
This thesis describes the synthesis, structures, and properties of two broad classes of inorganic solids, chalcohalides and intermetallics, with the common theme that they contain rare-earth (RE) elements, which belong to the set of critical minerals essential for many technological applications.
Quaternary rare-earth chalcohalides RE–M–Ch–X (M = d- or p-block metal or metalloid, Ch = chalcogen, X = halogen) represent a growing family of mixed-anion compounds, which remain relatively scarce compared to conventional “single-anion” compounds such as oxides, but offer the possibility of greater control over physical properties. Several series of compounds RE3Tt2Ch8I (RE = La, Ce, Pr; Tt = Si, Ge; Ch = S, Se) were prepared by direct combination of the elements at high temperatures. By gradual substitution of different proportions of Tt or Ch components in solid solutions of these semiconducting compounds, the band gap can be tuned within a range of 1.9 to 3.6 eV. The Ce-containing members exhibit blue luminescence, making them suitable candidates for applications in phosphor-converted white light emitting diodes. The emission behaviour can be controlled by changing the crystal field environment of Ch vs. I anions around the luminescent Ce3+ centres within these compounds.
Ternary rare-earth intermetallics RE–M–X (M = d-block metal; X = p-block metal or metalloid) have long been a rich source of quantum materials with exotic electrical and magnetic properties. Nevertheless, many aspects of their chemistry, including synthesis, phase stability, crystal structures, and chemical bonding remain poorly systematized and understood. Because reliable physical measurements depend on the availability of large single crystals or pure phase samples, efforts were made to apply flux methods for crystal growth of these compounds. In particular, ternary gallides RE−M−Ga (RE = La, Ce, Yb) were prepared in a gallium self-flux, and they were examined against a previously proposed stability diagram which predicts formation of ternary intermetallic phases. The new compound YbCu3Ga8 was discovered in this process, and the structure of YbNi3Ga9 was redetermined to resolve ambiguities in the literature. As examples of polar intermetallics, these compounds were confirmed by electronic structure calculations to exhibit multicenter covalent bonding within the anionic Ga networks. Similarly, crystal growth of ternary germanides REMGe (RE = Ce, Eu, Yb) was attempted in an indium flux to test a classification model. Crystals of RECo2Ge2 and CeIr2Ge2 were obtained, the latter exhibiting polymorphism with structures in two different space groups. The Yb-containing compounds Yb5Ir4Ge10 and Yb4Ir7Ge6 were also identified from the Yb−Ir−In−Ge reaction.
- Graduation date
- Fall 2023
- Type of Item
- Doctor of Philosophy
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.