The beneficial influence of tellurium on the thermoelectric properties of Mo3−xFexSb7

Various materials of the formulas Mo3−xFexSb7 and Mo2.6Fe0.4Sb7−yTey have been prepared by solid state synthesis at 873 K, starting from the elements in the stoichiometric ratios. The Fe content can be as high as x=0.45, while attempts to incorporate 0.5 Fe lead to the formation of FeSb2 as a minor side product. At x=0.4, the Te content can vary within 0≤y≤0.75, while the sample with y=1.0 shows FeSb2 as a minor phase. The materials were densified via hot-pressing, and their thermoelectric properties determined. Increasing both the Fe and the Te content leads to a decrease in the p-type carrier concentration, and thus an increase in Seebeck coefficient and a decrease in both electrical and thermal conductivity. In the end, the best thermoelectric properties were obtained in case of Mo2.6Fe0.4Sb6.25Te0.75, i.e. at the edge of the phase range, culminating in a figure-of-merit of zT=0.34 at 800 K. - Graphical abstract: Figure-of-merit of Mo3−xFexSb7−yTey. - Highlights: • Various Mo3−xFexSb7−yTey materials were synthesized and characterized. • In each case, the thermoelectric figure-of-merit increases rapidly with increasing temperature. • Higher Fe content and higher Te content cause a decrease of the p-type charge carriers. • With increasing Fe and Te, the Seebeck coefficient increases, while the electrical and thermal conductivity decreases. • Mo2.6Fe0.4Sb6.25Te0.75 shows the best thermoelectric properties of this series