Ultralow thermal conductivity and high thermoelectric figure of merit in mixed valence In5X5Br (X = S, and Se) compounds

Pandey, T and Nissimagoudar, AS and Mishra, A and Singh, AK (2020) Ultralow thermal conductivity and high thermoelectric figure of merit in mixed valence In5X5Br (X = S, and Se) compounds. In: Journal of Materials Chemistry A, 8 (27). pp. 13812-13819.

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Abstract

Discovering a material with a combination of high electrical conductivity, high thermopower, and low lattice thermal conductivity is crucial for designing efficient thermoelectric materials. Here, we show that a perfect balance of these properties can be realized in In5X5Br (X = S and Se) compounds, where indium simultaneously exists in three different oxidation states (In1+, In2+ and In3+). The presence of multiple charge carrier pockets near the band edge results in a high thermopower of 250-300 μV K-1 for both p- and n-type doping over a wide range of carrier concentrations and temperatures. Furthermore, our calculations find an exceptionally low lattice thermal conductivity of 0.55 W m-1 K-1 and 1.1 W m-1 K-1 for In5Se5Br and In5S5Br at room temperature, respectively. This ultralow lattice thermal conductivity is attributed to In1+, which is very weakly bound in the lattice. These In1+ atoms are located in a flat potential well and exhibit large mean square displacements demonstrating the strong anharmonic behavior. The strong anharmonicity was further confirmed by the large negative Grüneisen parameters. Remarkably, these compounds possess a rare combination of low thermal conductivity and high thermopower leading to an exceptionally high ZT of �2.4 and 2.7 for n-type In5S5Br and In5Se5Br, respectively, at high temperatures. The insights obtained from this work suggest an opportunity to discover efficient thermoelectric materials among other unexplored mixed valence compounds. © 2020 The Royal Society of Chemistry.

Item Type:	Journal Article
Publication:	Journal of Materials Chemistry A
Publisher:	Royal Society of Chemistry
Additional Information:	The copyright of this article belongs to Royal Society of Chemistry
Keywords:	Bromine compounds; Carrier concentration; Crystal lattices; Indium compounds; Potassium compounds; Selenium compounds; Thermal conductivity; Thermoelectric equipment; Thermoelectric power; Thermoelectric power plants; Thermoelectricity, High electrical conductivity; High temperature; Lattice thermal conductivity; Low thermal conductivity; Mean square displacement; Mixed valence compounds; Thermo-Electric materials; Thermoelectric figure of merit, Sulfur compounds
Department/Centre:	Division of Chemical Sciences > Materials Research Centre
Date Deposited:	31 Aug 2020 10:51
Last Modified:	31 Aug 2020 10:51
URI:	http://eprints.iisc.ac.in/id/eprint/66422

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