Binary and Unfilled Skutterudites from 1957 to 2026

Besides filled skutterudites with a high figure of merit, unfilled skutterudites also play an important role as thermoelectric materials; furthermore, they are easier to produce and do not need expensive rare earths as fillers. In the present review, thermoelectric properties (at 300 K and at the highest measured temperature) of more than 600 compositions from more than 230 publications between 1957 and 2025 were collected and evaluated. In various figures, the dependence of the peak ZT on the electrical resistivity, Seebeck coefficient, the power factor and the thermal conductivity is displayed for (i) binary CoSb3, for (ii) CoSb3 substituted at the Co-site, for (iii) substitution at the Sb-site or at both sites as well as for (iv) unfilled skutterudites without Co or Sb or Co and Sb. In most cases, the peak ZT equals the ZT at the highest measured temperature. Thermoelectric data are listed (i) to comply with the periodic chart and publishing year as well as (ii) in the form of a graphical overview of all discussed skutterudites. In this respect, this review will support the search for the ideal TE material for practical use.