The impact of the actual geometrical structure of a thermoelectric material on its electronic transport properties: The case of doped skutterudite systems

By doping CoSb(3) with Sn, Ba, and La, several structural outcomes are possible. The effect these different structures have on the electronic transport properties of the resulting materials is evaluated by means of an ab initio electronic structure approach and by using the semiclassical Boltzmann theory to derive the electronic transport properties from the band structure. It is shown that the calculated Seebeck coefficient is a very useful indicator of both the actual content of the dopant element and of where it mainly locates into the CoSb(3) structure. The use of such an indicator, along with geometrical considerations, demonstrates that the Sn atom occupies both the interstitial and the pnicogen ring positions with relative occupancies and ensuing thermoelectric properties, which heavily depend on the synthesis' conditions. The same indicator also suggests that the La atom, which occupies only interstitial positions, has a far lower maximal solubility in CoSb(3) than that claimed experimentally.