Skutterudites: A new class of promising thermoelectric materials

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Abstract
Based on literature data and experimental findings at the Jet Propulsion Laboratory (JPL), semiconductors with the skutterudite structure TPn3 (where T is a transition metal element such as Co, Rh, Ir, Ni, and Pd, and Pn is a pnicogen element such as P, As, and Sb) possess attractive characteristics and show a good potential for high ZT values. The high degree of covalency results in high mobility and low electrical resistivity values while a relatively complex 32 atom unit cell results in a reasonably low thermal conductivity. Both n‐type and p‐type electrical conductivity samples have been obtained. Room temperature Seebeck coefficient values up to 200 μVK−1 for p‐type and up to −600 μVK−1 for n‐type have also been measured on several of these materials. In addition, the large number of isostructural compounds, solid solutions and related phases offer many possibilities for optimization of the transport properties to a specific temperature range of thermoelectric applications. By replacing the transition metal or the pnicogen atom by two of its neighboring elements and ensuring that the number of valence electrons is retained, many ternary phases can be successfully derived from the original CoAs3 skutterudite structure. Some of these materials were found to have substantially lower thermal conductivities compared to those of the binary compounds. The composition, band gap and doping level can be tailored to achieve maximum performance. An overview of the results obtained to date is provided and our approach to achieving high ZT materials are discussed in this paper.

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