The Influence of Sn Additions on the Thermoelectric and Transport Properties of FeSb2Te-based Ternary Skutterudites

The influence of Sn additions was studied in a series of samples of a nominal composition FeSb2Te1-x Sn (x) (x = 0, 0.05, 0.1, 0.15, 0.2). SnTe compound was primarily identified in the matrix compound of the ternary skutterudite structure in the multiphase composite samples. It was determined that Sn atoms preferentially react with Te atoms which are present in order to form SnTe compound instead of entering the skutterudite structure. A detailed analysis of the composition of the ternary skutterudite matrix compound evoked by the striking similarities of the observed changes between the samples and another two published systems (FeSb2Te1-x Ge (x) and FeSb2+x Te1-x ) revealed the crucial role of the Sb/Te ratio as the dominant factor driving the observed changes of the measured properties. The anomalous changes of the measured transport properties values were explained in terms of an effective medium theory for two-phase FeSb2Te-SnTe composites. A maximum value of thermoelectric figure-of-merit, ZT = 0.47 at 673 K, was attained for the sample of a nominal composition FeSb2Te0.85Sn0.15.