Thermoelectric Behavior of Quantum Dots Engineered Bulk Half-Heusler Nanocomposites.

Thermoelectric Materials;Heulser Alloy;Materials Science and Engineering;Engineering;Materials Science and Engineering

Liu, YuanfengMillunchick, Joanna Mirecki ;

University of Michigan

关键词: Thermoelectric Materials;    Heulser Alloy;    Materials Science and Engineering;    Engineering;    Materials Science and Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/113524/yuanfeng_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Over the past 20 years, thermoelectric materials have received more and more attention due to dwindling natural resources and inefficient energy conversion systems. In this thesis, focus was placed on the development of half-Heusler based nanocomposite materials for application in thermoelectric technology. Half-Heusler alloys were chosen as our research focus due to its environmentally friendly nature, cheap elemental constituents, and their robust mechanical stability relative to other thermoelectric materials. Half-Heuslers with 18 valence electrons are narrow band gap semiconductors with large Seebeck coefficients. Detrimentally, however, the thermal conductivity can reach ~ 10 Wm-1K-1. In order to improve the thermoelectric properties of half-Heusler, two main strategies were applied. The first strategy is to increase mass fluctuation or point defects in the sample during solid-state reaction. The second strategy is to add a doping element to tune the carrier density or other phases to form additional phonon scattering centers. This work focuses on the effects of(1) the full-Heusler (FH) second phase, (2) heavy doping via Sb substitution at Sn sites, and (3) band gap engineering through Ge substitution at Sn sites on the electronic and thermal properties of half-Heusler (HH) matrices with composition Ti0.1Zr0.9NiSn. Additionally, (4) the concept of energy filtering at HH/FH interfaces on Zr0.25Hf0.75Ni1+xSn1-ySby composites with varying doping levels is investigated. And lastly, (5) we explore the effect of varying chemical composition of the FH inclusions on the electronic and thermal properties of HH phases. This is achieved by the reaction of elemental Co with polycrystalline powder with composition Zr0.25Hf0.75NiSn.