Aikinite as a potential thermoelectric material with ultra-low thermal conductivity Shriparna Mukherjee 1 , Virginia Carnevali 2 , David J Voneshen 3 , Marco Fornari 2 , Anthony V. Powell 1 , Paz Vaqueiro 1 1 University of Reading, UK, 2 Central Michigan University, USA, 3 Rutherford Appleton Laboratory, UK Intrinsically low thermal conductivity is a favorable parameter for efficient thermoelectric materials 1 . Moreover, for the widespread implementation of thermoelectric (TE) energy recovery, it is important to identify tellurium- free materials with good TE performance. In this context, sulfide minerals 2 such as tetrahedrites and colusites are attracting much interest. Here, we present work on the mineral aikinite, CuPbBiS 3 , which adopts a structure closely related to that of Bi 2 S 3 , which itself exhibits promising TE properties 3 . Aikinite samples were prepared by mechanical alloying followed by heat treatment. Rietveld refinement of powder neutron diffraction data, collected on POWGEN (SNS, ORNL), indicate that the isoelectronic Pb 2+ and Bi 3+ cations are fully ordered. Moreover, Cu + and Pb 2+ have larger atomic displacement parameters than Bi 3+ . The thermal conductivity, measured on hot-pressed pellets, exhibits a remarkably low value of ca. 0.54 W m -1 K -1 at room temperature. The calculated vibrational density of states exhibits Einstein-like phonon modes at 100 cm -1 , attributed to Cu + vibrations, and low- frequency optical phonon modes below 50 cm -1 (at ~ 4.5 meV), arising from Pb 2+ vibrations. The experimentally determined vibrational phonon density of states is in very good agreement with calculations. Inelastic neutron scattering data, collected on LET (ISIS), confirms the presence of low-energy vibrational modes (~ 4 meV), which are likely to be responsible for the ultralow thermal conductivity. The temperature dependence of the low-energy Pb 2+ vibrational mode is consistent with anharmonic behaviour, while the Cu + Einstein-like mode softens markedly with increasing temperature. The results of this work will be presented here. References
1. T. Ghosh et al ., J. Am. Chem. Soc. 144 , 23 (2022), 2. A.V. Powell, J.Appl.Phys. 126 , 100901 (2019). 3. Ohmasa and Nowacki, Zeitschrift für Kristallographie - Crystalline Materials, 132 ,71 (1970).
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