Lone pair rotation and bond heterogeneity leading to ultralow thermal conductivity in aikinite

Carnevali, V., Mukherjee, S., Voneshen, D. J., Maji, K., Guilmeau, E., Powell, A. V., Vaqueiro, P. ORCID: https://orcid.org/0000-0001-7545-6262 and Fornari, M. (2023) Lone pair rotation and bond heterogeneity leading to ultralow thermal conductivity in aikinite. Journal of the American Chemical Society, 145 (16). pp. 9313-9325. ISSN 0002-7863 doi: 10.1021/jacs.3c02536

Abstract/Summary

Understanding the relationship between crystal structure, chemical bonding and lattice dynamics is crucial for the design of materials with low thermal conductivities, which are essential in fields as diverse as thermoelectrics, thermal barrier coatings, and optoelectronics. The bismuthinite-aikinite series, Cu1–x□xPb1–xBi1+xS3 (0 <= x <= 1, where □ represents a vacancy), has recently emerged as a family of n-type semiconductors with exceptionally low lattice thermal conductivities. We present a detailed investigation of the structure, electronic properties and the vibrational spectrum of aikinite, CuPbBiS3 (x=0), in order to elucidate the origin of its ultralow thermal conductivity (0.48 W m-1 K-1 at 573 K), which is close to the calculated minimum for amorphous and disordered materials, despite its polycrystalline nature. Inelastic neutron scattering data reveal an anharmonic optical phonon mode at ca. 30 cm-1, attributed mainly to the motion of Pb2+ cations. Analysis of neutron diffraction data, together with ab initio molecular dynamics simulations, shows that the Pb2+ lone pairs are rotating and that, with increasing temperature, Cu+ and Pb2+ cations, which are separated at distances of ca. 3.3 Å, exhibit significantly larger displacements from their equilibrium positions than Bi3+ cations. In addition to bond heterogeneity, a temperature-dependent interaction between Cu+ and the rotating Pb2+ lone pair is a key contributor to the scattering effects that lower the thermal conductivity in aikinite. This work demonstrates that coupling of rotating lone pairs and vibrational motion is an effective mechanism to achieve ultralow thermal conductivity in crystalline materials.

Item Type	Article
URI	https://reading-clone.eprints-hosting.org/id/eprint/111416
Identification Number/DOI	10.1021/jacs.3c02536
Refereed	Yes
Divisions	Life Sciences > School of Chemistry, Food and Pharmacy > Department of Chemistry Interdisciplinary centres and themes > Energy Research Interdisciplinary centres and themes > Chemical Analysis Facility (CAF) > Thermal Analysis (CAF) Interdisciplinary centres and themes > Chemical Analysis Facility (CAF) > Xray (CAF)
Publisher	American Chemical Society
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