Low thermal conductivity in Bi₈CsO₈SeX₇ (X = Cl, Br) by combining different structural motifs

Newnham, Jon A, Gibson, Quinn D, Surta, T Wesley ORCID: 0000-0002-2882-6483, Morscher, Alexandra, Manning, Troy D ORCID: 0000-0002-7624-4306, Daniels, Luke M ORCID: 0000-0002-7077-6125, Claridge, John B ORCID: 0000-0003-4849-6714 and Rosseinsky, Matthew J ORCID: 0000-0002-1910-2483 (2023) Low thermal conductivity in Bi₈CsO₈SeX₇ (X = Cl, Br) by combining different structural motifs JOURNAL OF MATERIALS CHEMISTRY A, 11 (29). pp. 15739-15748. ISSN 2050-7488, 2050-7496

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Abstract

Understanding the structure-property relationships of materials in order to supress thermal conductivity is crucial for developing efficient thermoelectric generators and thermal barrier coatings. Low thermal conductivity materials can often contain a single dominant phonon scattering mechanism. Here, we highlight how combining different structural features into one material can aid in the design and identification of new materials with low thermal conductivities. We synthesise two new mixed-anion materials, Bi<inf>8</inf>CsO<inf>8</inf>SeX<inf>7</inf> (X = Cl and Br), with low thermal conductivities of 0.27(2) and 0.22(2) W m⁻¹ K⁻¹ respectively, measured along their c-axes at room temperature. The Bi<inf>8</inf>CsO<inf>8</inf>SeX<inf>7</inf> materials possess a combination of bond strength hierarchies, Cs⁺ vacancies, and low frequency Cs⁺ rattling. These different features significantly inhibit phonon transport along different crystallographic directions. Due to sharp bond strength contrast between the van der Waals gaps and [Bi<inf>2</inf>O<inf>2</inf>]²⁺ layers, the Bi<inf>8</inf>CsO<inf>8</inf>SeX<inf>7</inf> materials exhibit thermal conductivities <50% of the theoretical minimum when measured along the stacking direction. Conversely, the thermal conductivity associated with the ab-plane is reduced by Cs⁺ rattling when compared to the structurally and compositionally related BiOCl.

Item Type:	Article
Uncontrolled Keywords:	3403 Macromolecular and Materials Chemistry, 34 Chemical Sciences
Divisions:	Faculty of Science & Engineering > School of Physical Sciences
Depositing User:	Symplectic Admin
Date Deposited:	29 Sep 2023 15:40
Last Modified:	16 Jun 2026 11:07
DOI:	10.1039/d3ta01630g
Open Access URL:	https://doi.org/10.1039/D3TA01630G
Related Websites:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3173239
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