Thermoelectric materials are increasingly attracting attention due to their potential for use in devices for waste heat energy recovery. Bismuth copper oxychalcogenides have been recently identified as promising p-type thermoelectric materials. The origin of their promising performance lies in their extremely low thermal conductivity, which approaches values normally found in amorphous materials. We seek to exploit inelastic neutron scattering to determine the neutron-weighted phonon density of states, which will be compared with the phonon density of states determined by first-principle calculations. This results will enable us to elucidate the origin of the unusually low thermal conductivity. This experiment will complete a body of work on these materials carried out by a PhD student.