Skutterudites: A phonon-glass-electron crystal approach to advanced thermoelectric energy conversion applications

Recently there has been a resurgence of research efforts related to the inv estigation of new and novel materials for small-scale thermoelectric refrig eration and power generation applications. These materials need to couple a nd optimize a variety of properties in order to exhibit the necessary figur e of merit, i.e. the numerical expression that is commonly used to compare one potential thermoelectric material with another. The figure of merit is related to the coefficient of performance or efficiency of a particular dev ice made from a material. The best thermoelectric material should possess t hermal properties similar to that of a glass and electrical properties simi lar to that of a perfect single-crystal material, i.e. a poor thermal condu ctor and a good electrical conductor. Skutterudites are materials that appe ar to have the potential to fulfill such criteria. These materials exhibit many types of interesting properties. For example, skutterudites are member s of a family of compounds we call open structure or cage-like, materials. When atoms are placed into the interstitial voids or cages of these materia ls, the lattice thermal conductivity can be substantially reduced compared with that of unfilled skutterudites. These compounds exhibit electrical pro perties ranging from that of low-temperature superconductors to narrow gap semiconductors.