Thermoelectric performance of mischmetal skutterudites MmyFe4−xCoxSb12 at elevated temperatures

Abstract Thermoelectric behaviour was studied for Mm y Fe 4− x Co x Sb 12 with x  = 0 and 1 (Mm is mischmetal) within the temperature range from 300 K to 800 K and was compared with data for corresponding Ce y Fe 4− x Co x Sb 12 . No decrease of thermal conductivity at high temperatures was observed changing from a single atom filler (Ce) to a multi-element filler (Mm). The electrical resistivity of Mm y Fe 4− x Co x Sb 12 was found to be lower than or similar to that of Ce y Fe 4− x Co x Sb 12 . Accordingly the figure of merit for MmFe 3 CoSb 12 exceeds 1 at temperatures above 600 K. The influence of several parameters such as impurity phases and grain size on the thermoelectric performance of Mm y Fe 4− x Co x Sb 12 was investigated. FeSb 2 and Sb have little effect on the figure of merit whilst the presence of MmSb 2 and oxides reduces the thermoelectric performance, when these phases are segregated at the grain boundaries. The decrease of the crystallite size from micro scale (20–100 μm) to nano-scale (100–300 nm) in all cases improves the figure of merit by about 20%. Dislocations have no influence on ZT since the dislocation density after hot pressing is as low as 10 12  m −2 .