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Synthesis and Optimization of Praseodymium Telluride System Through Alloys and Composites.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Synthesis and Optimization of Praseodymium Telluride System Through Alloys and Composites./
Author:	Hogan, Brea Elizabeth.
Description:	1 online resource (137 pages)
Notes:	Source: Dissertations Abstracts International, Volume: 85-03, Section: B.
Contained By:	Dissertations Abstracts International85-03B.
Subject:	Materials science. -
Online resource:	click for full text (PQDT)
ISBN:	9798380378956

Synthesis and Optimization of Praseodymium Telluride System Through Alloys and Composites.
Hogan, Brea Elizabeth.

Synthesis and Optimization of Praseodymium Telluride System Through Alloys and Composites. - 1 online resource (137 pages)

Source: Dissertations Abstracts International, Volume: 85-03, Section: B.

Thesis (Ph.D.)--University of California, Los Angeles, 2023.

Includes bibliographical references

Radioisotope Thermoelectric Generators (RTGs) provide electrical power for spacecraft by converting heat generated by the decay of plutonium-238 (Pu-238) into electricity. In missions such as Curiosity, the excess heat generated from an RTG can be used as a convenient and steady source of warmth to maintain proper operating temperatures for a spacecraft and its instruments in cold environments. While RTGs have been historically viewed as a highly reliable power option, current RTGs have relatively low system efficiencies on the order of 6%. This clearly highlights the need to concentrate research in this field to improve overall efficiencies. To accomplish this, vast improvements on thermoelectric materials are necessary for the success and longevity of future space emissions.The figure of merit to determine the efficiency of thermoelectric materials is defined as \uD835\uDC4D\uD835\uDC47=(\uD835\uDF0E\uD835\uDC462 /\uD835\uDF05)T where σ, S, κ, and T are electrical conductivity, Seebeck coefficient, thermal conductivity, and temperature, respectively. Rare earth chalcogenides with the Th3P4-type structure (such as La3-xTe4) can accommodate vacancies on the rare earth site, leading to disorders and distortions in the lattice, and in turn enhanced phonon scattering. This ultimately results in a reduction in the lattice thermal conductivity of ~0.4-0.8 W/m-k. Previously reported optimized defect stoichiometry (LaTe1.46) attained ZT=1.1 around 1275K. Previous research conducted at JPL indicates that improvements are seen within Pr3Te4 and Nd3Te4 compared to La3Te4, primarily due to the contribution of the f-states to the density of states near the Fermi level. This ultimately contributes to an improvement in Seebeck, and thus an improvement in ZT.One of the main projects of this dissertation is to better understand the oxidation kinetics across RE3Te4 (RE = rare earth: La, Pr, Nd). Understanding kinetics for these materials using thermogravimetric analysis (TGA) will help us to further mitigate the effects of oxidation and improve the efficiencies of these materials for long-term, deep space missions. Research indicates that rare earth tellurides experience similar oxidation mechanisms, but at distinct rates. Pr3Te4 and Nd3Te4 oxidize kinetically faster compared to La3Te4, which would suggest there is less time for the formation of intermediate phases.Another project discussed in this research is focused on the synthesis and characterization of thermoelectric systems with the potential for higher thermoelectric conversion efficiency such as La3-xRExTe4 (RE = Pr) to develop high-performance radioisotope thermoelectric generators. It is hypothesized that alloying in the La3-xPrxTe4 system will tune the DOS via f-electrons, which will help reduce thermal conductivity because of point defect scattering, and mechanical improvements will be seen via solid solution strengthening. The rule of mixtures was scientifically proven due to the alloy thermoelectric properties residing between the properties of the end members. Hardness measurements indicate that the end members and the alloys all have similar hardness values within error.The final project is focused on understanding the CAFE (composite-assisted funneling of electrons) effect on PrTe1.46 composites and their thermoelectric properties. Ni composites within PrTe1.46 have not been previously investigated; thus, this research will discern how the CAFE effect exhibits itself within a Pr3Te4 matrix. It is hypothesized that a significant decrease in electrical resistivity will occur compared to LaTe1.46-Ni composites, due to the improvement in ZT observed with PrTe1.46 compared to LaTe1.46. ZT values for 5% volume Ni increased the average ZT, while the 10% and 15% volume Ni resulted in an improvement in peak ZT at 1275K. The resultant increase cannot be attributed to the CAFE effect due to the Seebeck and resistivity coupling.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2024

Mode of access: World Wide Web

ISBN: 9798380378956Subjects--Topical Terms:

557839
Materials science.
Subjects--Index Terms:

Praseodymium tellurideIndex Terms--Genre/Form:

554714
Electronic books.

Synthesis and Optimization of Praseodymium Telluride System Through Alloys and Composites.
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