Sustainable energy-conversion technologies are important for ensuring our energy supply against declining fossil fuel reserves. Thermoelectric materials offer great potential for the conversion of waste heat energy into useful electrical energy. As part of a collaborative research project, which seeks to implement thermoelectric energy recovery in automotive exhaust systems, we are investigating the structure and properties of skuterudites, which are materials with attractive thermoelectric properties. In the course of this work, we have discovered that isoelectronic substitution of cobalt with a 50:50 mixture of Fe and Ni in the CoSb3 skutterudite results in a marked reduction in thermal conductivity. The origin of this effect is not clear, and we seek to exploit inelastic neutron scattering to understand the evolution of vibrational properties with changing framework composition.