Enhanced covalency and nanostructured-phonon scattering lead to high thermoelectric performance in n-type PbS

Rathore, E and Juneja, R and Sarkar, D and Roychowdhury, S and Kofu, M and Nakajima, K and Singh, AK and Biswas, K (2022) Enhanced covalency and nanostructured-phonon scattering lead to high thermoelectric performance in n-type PbS. In: Materials Today Energy, 24 .

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Abstract

High thermoelectric performance can be achieved either by tuning the electronic structure or by enhancement in scattering the heat-carrying phonons, which often affect each other. Thereby, a leap in the performance can be achieved by simultaneous modulation of electronic structure and lowering of thermal conductivity. Herein, we demonstrate a high thermoelectric figure of merit (zT) of 1.45 at 900 K for Ge doped (4�10 mol) n-type PbS, which is the one of the highest values among all n-type PbS-based thermoelectric materials. This high performance is achieved by simultaneous (a) enhancement of covalency in chemical bonding which increases the electrical conductivity, and (b) reduction of lattice thermal conductivity (κlat) to an ultra-low value of 0.56 W m�1K�1 at 900 K by the introduction of nanometer-sized (5�10 nm) precipitates of Pb2GeS4 in PbS matrix which strongly scatter the heat-carrying phonons. The presence of low-lying transverse acoustic (TA) and longitudinal acoustic (LA) phonon modes at 48.24 cm�1 and 91.83 cm�1, respectively are experimentally revealed from inelastic neutron scattering (INS) experiments. The softening of low-frequency modes at a higher temperature and ultra-short phonon lifetime (1�4.5 ps) further explain the ultra-low κlat. Electron localization function (ELF) analysis confirms chemical bonding hierarchy and increased covalent bonding due to the presence of Ge in PbS. The increase in bond covalency upon Ge doping in n-type PbS weakens electron�phonon coupling, thereby increasing the electrical transport. © 2022 Elsevier Ltd

Item Type:	Journal Article
Publication:	Materials Today Energy
Publisher:	Elsevier Ltd
Additional Information:	The copyright for this article belongs to Elsevier Ltd
Keywords:	Chemical analysis; Chemical bonds; Electronic structure; Germanium; Germanium compounds; Inelastic scattering; IV-VI semiconductors; Lead compounds; Neutron scattering; Phonons; Thermal conductivity; Thermoelectric equipment; Thermoelectricity, Bonding heterogeneity; Chemical bondings; Covalencies; Electronic.structure; Heat carrying phonons; Low thermal conductivity; Nano-structured; Thermoelectric; Thermoelectric performance, Sulfur compounds
Department/Centre:	Division of Chemical Sciences > Materials Research Centre
Date Deposited:	16 Mar 2022 06:06
Last Modified:	16 Mar 2022 06:06
URI:	http://eprints.iisc.ac.in/id/eprint/71436

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