Introducing Ordered Silicon Vacancies Into WSi2

Author

Grace M. Atkins, Missouri State UniversityFollow

Date of Graduation

Fall 2024

Degree

Master of Science in Chemistry

Department

Chemistry & Biochemistry

Committee Chair

Fei Wang

Abstract

Thermoelectric materials are very useful in industry due to their unique ability to convert waste heat into electricity. One such reported thermoelectric material is rhenium silicide (ReSi_1.75▯_0.25), resulting from ordered silicon vacancies in its crystal structure. The purpose of this project is to dope tungsten silicide (WSi₂) with more electron rich elements to find a ternary silicide with a similar crystal structure to ReSi_1.75▯_0.25, in order to synthesize a less expensive thermoelectric material. Two synthesis methods are used in this project to dope WSi₂. Powder x-ray diffraction (XRD) was used to evaluate the final phase doped ternaries by comparison to the undoped WSi₂ pattern. The first method using pure phase binary pnictides and chalcogenides with tungsten as precursors to introduce P, S, and Se into the ternary W silicide structure. The ternary silicides prepared, using WP as the source of P, were found to contain an unknown phase in addition to WSi₂, but did not show evidence of ordered Si vacancies. The second method uses the more electron rich transition metals Ru, Fe, and Mn as dopants. Annealing showed to have no effect on the final phase for the Ru series, but changed the phase significantly for the Fe and Mn series. Based on the lack of peak shifting for primary phase WSi₂-type compositions, there was no replacement of W atoms in the WSi₂ unit cell with any of the other transition metal dopants, resulting in multiphase structures. Using single crystal precession image analysis, no satellite reflections were present for any series, indicating no ordered Si vacancies existing in any of the ternary doped W silicides. Because of this lack of ordered vacancies, thermoelectric properties like those in ReSi_1.75▯_0.25 are not proven.

Keywords

Thermoelectric materials, silicon vacancies, peak shifting, satellite reflections, doped ternary silicide, multiphase structure

Subject Categories

Chemistry | Inorganic Chemistry

Copyright

© Grace M. Atkins

Recommended Citation

Atkins, Grace M., "Introducing Ordered Silicon Vacancies Into WSi2" (2024). MSU Graduate Theses/Dissertations. 4019.
https://bearworks.missouristate.edu/theses/4019