Understanding the amide-assisted synthesis and olivine structure-directed twinning of Fe₂GeS₄ nanoparticles
| dc.contributor.author | Miller, Rebecca Caroline, author | |
| dc.contributor.author | Prieto, Amy L., advisor | |
| dc.contributor.author | Shores, Matthew P., committee member | |
| dc.contributor.author | Sites, James R., committee member | |
| dc.contributor.author | Ackerson, Christopher J., committee member | |
| dc.date.accessioned | 2020-08-31T10:11:49Z | |
| dc.date.available | 2021-08-24T10:11:49Z | |
| dc.date.issued | 2020 | |
| dc.description.abstract | The reality of detrimental anthropogenic effects on the environment requires the development of a number of sustainable practices and technologies. The Prieto Group strives to advance the synthesis and understanding of materials for use in energy conversion and storage. Advances in computational solid-state chemistry have resulted in the identification of a number of earth-abundant, relatively non-toxic compounds as promising photovoltaic absorber materials. However, the synthesis of solids remains a step behind, requiring empirical exploration of precursors and conditions. As reaction intermediates and mechanisms are discovered, general synthetic strategies can be translated from one material system to the next. Inorganic nanoparticle (NP) syntheses rely on the interdisciplinary expertise of solid-state, organometallic, and organic chemistry and show interesting complexity. The work herein has advanced the understanding of amide-assisted NPs syntheses and examined the microstructure of twinned Fe2GeS4 NPs. Chapter 1 presents a history of solution-based, amide-assisted NP reactions. As scientists understand the in situ speciation of precursors, more efficient reactions can be designed. This understanding allows the use of more benign and safe (both in terms of human and environmental) precursors and provides higher synthetic control over the end products. The presence of amide bases has generally provided access to higher NP nucleation rates and accessed smaller, more monodisperse particles. The increased monomer reactivity has also allowed the formation of ternary NPs free from binary or unary impurities by balancing the reactivity of cations of different valency. The most common amide base is LiN(SiMe3)2, and I relate this field to the use of its conjugate acid, hexamethyldisilazane or HMDS, in NP syntheses. Its addition has aided the production of NPs, but its chemical role remains unclear. This chapter was written utilizing a portion of an invited review paper written by myself, Jennifer M. Lee, Lily J. Moloney, and Amy L. Prieto in the Journal of Solid State Chemistry (2019, 273, 243-286.). Section 2.2 of the review outlined the evolution of understanding of amide-assisted NP syntheses and was adapted and expanded upon herein. In Chapter 2, I report the redesign of a Fe2GeS4 NP synthesis. In 2013, the Prieto group was the first to report a NP synthesis for the compound, which had been predicted to be a promising photovoltaic absorber material in 2011. The original reaction relied on HMDS as an additive and employed the highly-reactive S precursor, hexamethyldisilathiane. Herein, I speculate on these precursors' roles and exchange their use for LiN(SiMe3)2 and S powder, eliminating the formation of an Fe1–xS intermediate and reducing the growth time from 24 h to 10 min. I thoroughly map the reaction landscape of this system and provide structural, compositional, and optical characterization of the particles. This work was published in the Journal of the American Chemical Society (J. Am. Chem. Soc. 2020, 142 (15), 7023–7035.). The Fe2GeS4 NPs show an interesting star-shaped morphology, so I examine the microstructure via electron microscopy and identify the presence of crystal twinning in Chapter 3. The particles exist as three sets of stacked nanoplates intersecting at 60˚ angles, which forms a triplet of twins or trillings. In the products, 98% of the particles are twinned. Because crystal twinning, and especially trilling formation, in macroscopic crystals is rare, a synthetic route to a massive collection of twinned particles stands as a valuable resource for understanding the fundamentals of crystal twinning in olivine compounds. I relate the twinning to the underlying hexagonal pseudosymmetry of the orthorhombic, olivine crystal structure. Because of the ratio of the unit cell dimensions (a_Pnma/b_(Pnma )≈√3), the compound is susceptible to forming twins with growth of the [010] direction off the {310} faces. This can occur for other olivine compounds of similar unit cell dimension ratios, so I rank all of the olivine compounds listed in the Inorganic Crystal Structure Database according to this metric in Appendix A. This chapter is a manuscript prepared for submission. Finally, Chapter 4 outlines our recommendations for future work to advance the understanding of amide-assisted NP syntheses and translate this synthetic system to other compounds. I suggest the systematic development of SnS NP reactions utilizing each of the precursors: Sn silylamide, alkali silylamides, and HMDS. I outline a set of complementary techniques to characterize the reaction intermediates and mechanisms. This type of investigation has been done by the Kovalenko group for the formation of unary Sn0 NPs, but the interaction of the chalcogen species remains unknown. Further, no systematic mechanistic study exists for the use of HMDS in NP synthesis. This work would advance the understanding and use of amide-assisted syntheses for all metal chalcogenide compounds. In addition, I present preliminary data in our extrapolation of the Fe2GeS4 NP synthesis to the following solid solutions: Fe2GeS4–xSe (including the end member Fe2GeSe4) and Fe2–xMnxGeS4. One composition of each solid solution was formed and characterized by powder X-ray diffraction, and I present electron microscopy to show twinning in the Fe2GeS4–xSex (x = 0.96, 24 mol% Se) NPs. Lastly, I consider the possibility for twinning in an important olivine compound for battery science, LiFePO4, which is a common cathode material. The crystal structure shows a high degree of hexagonal pseudosymmetry, indicating that the energetics of forming twin domains may be favorable. I discuss the possible ramifications this may have on battery cycling performance. Thus, the scope of this work focuses on one compound, Fe2GeS4, but investigation into its synthesis and microstructure has opened a number of avenues for promising research. This compound itself presents a promising material for both photovoltaic and thermoelectric energy conversion, and the syntheses herein provide a launching point for property measurement and application evaluation. Further, the general examination of twinning in olivine compounds identifies questions for evaluating the function of other compounds useful for a number of applications. Lastly, analogous calculations to the geometrical evaluation done for orthorhombic olivine compounds could be carried out for other crystal structure types with unit cells that exist close to higher orders of symmetry. The advances presented herein on understanding the reactivity and roles of NP precursors are fundamental for progressing the field of NP synthesis. The reproducible formation and structural characterization of these twinned NPs provide a promising system for future explorations in crystal twinning and its effect on material properties. | |
| dc.format.medium | born digital | |
| dc.format.medium | doctoral dissertations | |
| dc.identifier | Miller_colostate_0053A_16094.pdf | |
| dc.identifier.uri | https://hdl.handle.net/10217/211768 | |
| dc.language | English | |
| dc.language.iso | eng | |
| dc.publisher | Colorado State University. Libraries | |
| dc.relation.ispartof | 2020- | |
| dc.rights | Copyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright. | |
| dc.subject | olivine | |
| dc.subject | synthesis | |
| dc.subject | nanoparticle | |
| dc.subject | twinning | |
| dc.subject | photovoltaics | |
| dc.title | Understanding the amide-assisted synthesis and olivine structure-directed twinning of Fe₂GeS₄ nanoparticles | |
| dc.type | Text | |
| dcterms.embargo.expires | 2021-08-24 | |
| dcterms.embargo.terms | 2021-08-24 | |
| dcterms.rights.dpla | This Item is protected by copyright and/or related rights (https://rightsstatements.org/vocab/InC/1.0/). You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). | |
| thesis.degree.discipline | Chemistry | |
| thesis.degree.grantor | Colorado State University | |
| thesis.degree.level | Doctoral | |
| thesis.degree.name | Doctor of Philosophy (Ph.D.) |
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