Thermoelectric (TE) materials enable the recovery of useful electrical energy from waste heat. High-efficiency requires a high electrical conductivity to be coupled with a high Seebeck coefficient and low thermal conductivity. The very low thermal conductivity of bornite, a naturally occurring copper-iron sulphide, makes it an attractive candidate TE material. Our investigations into improving the electrical properties of bornite without impairing the thermal conductivity have led to the discovery of synthetic analogues that show excellent TE performance. We wish to investigate the detailed structure of these materials by powder neutron diffraction. We will study the evolution of cation/vacancy ordering through two structural transitions and the behaviour of the copper sub-lattice, which appears to be responsible for a reduction in lattice thermal conductivity.