Ultralow thermal conductivity in aikinite, CuPbBiS3

There is a need for thermoelectric materials that do not contain tellurium, a rare element in the Earth's crust, to enable widespread implementation of thermoelectric energy recovery. High-throughput calculations led us to identify the mineral aikinite, CuPbBiS3, as a potential thermoelectric material. Our calculated vibrational density-of-states suggests that copper rattling and anharmonicity, arising from the presence of a lone pair on the lead cation, should result in low thermal conductivity. Experimentally, we have found that the thermal conductivity of aikinite at room temperature is remarkably low (< 0.6 W m-1K-1). Here, we seek to exploit inelastic neutron scattering to provide direct evidence for the presence of the low-energy vibrational modes predicted by our calculations.