Graduation Semester and Year
Fall 2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Chemistry
Department
Chemistry and Biochemistry
First Advisor
Robin T. Macaluso
Abstract
Heteroanionic materials, where more than one anionic species is present in the material, have emerged as a distinct class of solid-state compounds for targeting new materials and tuning desirable physical properties. Greater structural diversity afforded by the expanded compositional phase space presents an opportunity for materials discovery. The broad range of anion characteristics can be advantageously combined and often results in interesting features otherwise inaccessible through a conventional heterocationic approach or homoanionic systems. Among heteroanionic compounds, oxychalcogenides, which contain an oxygen and at least one chalcogen species (i.e. sulfur, selenium, tellurium), are exciting materials with many promising technological applications including transparent semiconductors, solid-state electrolytes, thermoelectrics, and optoelectronics. However, oxychalcogenides are relatively understudied and the advancement of these materials is impeded by a lack of mechanistic understanding of reaction pathways. This work contributes to the continued development of oxychalcogenides by systematically following product formation of rare-earth oxychalcogenides prepared by traditional solid-state routes and by gas-assisted reaction routes. A survey of ternary and quaternary rare-earth oxychalcogenides is presented in Chapter 2, with a focus on the structural diversity and unique synthetic approaches which enable them. Investigations of the heteroanionic rare-earth oxytelluride Ln2O2Te (Ln = La – Pr) reveal a reversible phase transition to the tellurate Ln2TeO6 and highlight the outstanding versatility of tellurium in terms of its structures, properties, and reactivities. Detailed synthetic conditions showcase the broad range of Te oxidation states from 2− to 6+ which can be accessed by heating in the appropriate reducing/oxidizing atmosphere. A comparison of two different synthetic routes demonstrates the effects of synthetic parameters on the structure & properties of lanthanum oxytellurides. A combination of ex situ techniques is used to elucidate distinct characteristics between the bulk structures and monitor product formation to gain insight into growth mechanisms as well as the conditions that favor crystal formation of the oxytelluride. Differences in optical properties at the macroscopic scale are examined and fall in the semiconducting range. Exploration of reaction pathways and phase transitions using powerful in situ X-ray and neutron diffraction techniques unveil a structural intermediate phase between Ln2O2Te and Ln2TeO6. Finally, the reversible thermochromic behavior of the rare-earth oxyselenide La4O4Se3 is discussed. These studies provide novel information on oxychalcogenide chemistry and if exploited creatively, may facilitate an expansion of oxychalcogenide materials.
Keywords
Heteroanionic, Oxytelluride, Oxyselenide, Materials Chemistry, Mixed-Anion, Neutron Diffraction, Semiconductor, Layered Structures, Ln2O2Te, La4O4Se3
Disciplines
Inorganic Chemistry | Materials Chemistry
License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Recommended Citation
Orr, Melissa S., "Exploring Solid-State Reaction Pathways and Physical Properties of Rare-Earth Oxychalcogenides" (2024). Chemistry & Biochemistry Dissertations. 278.
https://mavmatrix.uta.edu/chemistry_dissertations/278