Date of Award

31-8-2024

Document Type

Thesis

School

School of Electrical & Electroncis Engineering

Programme

Ph.D.-Doctoral of Philosophy

First Advisor

Dr.M.Sridharan

Keywords

Thermoelectric Materials, p-Type Magnesium Antimonide (p-Type Mg3Sb2), Thermopower, Seebeck Coefficient, Point Defect Phonon Scattering

Abstract

Recently, there has been growing research in the scientific community regarding the conversion of heat flux into electricity, which has proven effective in mitigating energy crises. Solid-state thermoelectric (TE) devices use the Seebeck effect to efficiently convert waste heat into electricity. Traditional materials contain toxic, rare, and expensive elements like Lead, Tellurium, and Germanium that restrict large-scale production, commercialization, and practical utilization.

Recently, Mg3Sb2-based materials have been attractive due to their remarkable characteristics, including abundance, affordability, and environmental friendliness. Furthermore,n-type Mg3Sb2-based materials exhibit high TE performance because of their high band degeneracy in the conduction band minimum (CBM), and low lattice thermal conductivity contributes to the enhanced TE performance of n-type Mg3Sb2-based materials. However, p-type Mg3Sb2-based material has a lower TE performance, highlighting the importance of improving it.

Herein, we focus on the p-type Mg3Sb2-based material mid-temperature thermoelectric application. Mg3Sb2- based materials have been synthesized through the solid-state reaction by evacuation-and-encapsulation technique. The thermoelectric transport behaviour of the samples has been investigated and optimized the Figure of merit (zT) of the p-type Mg3Sb2-based materials such as (i) Sn doped p-type Mg3Sb2 material, (ii) p-type Mg3-xZnxSb2/Sb composites: the role of ZnSb/Sb composite, and (iii) Zn and Ag co-doped p-type Mg3Sb2.

Among them, the Mg2Zn1-yAgySb2 (y = 0.03) sample has the highest zT of 0.95 at 725 K. Ga-doped n-type Mg3Sb2 was synthesized and studied its structural and thermoelectric transport behaviour. A prototype thermoelectric generator has been fabricated with the 8-pairs using p-leg Mg2Zn0.97Ag0.03Sb2 and n-leg Mg3.24Ga0.06Sb1.48Bi0.48Te0.04 materials. The maximum efficiency of 5.68% at the TH = 700 K was achieved for the fabricated device.

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