Co x Ni4−x Sb12−y Sn y skutterudites: processing and thermoelectric properties
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N-type and p-type skutterudite samples with the composition Co x Ni4−x Sb12−y Sn y were synthesized with composition range 0 < x < 2 and 3 < y < 5. Samples were pre-processed by solidification into ingots. Skutterudite phase formation was achieved by mechanical alloying the crushed ingots. The milled powders were consolidated to dense pellets by hot pressing. Thermoelectric measurements showed limited high-temperature performance below 400 °C. Skutterudite decomposition above 250 °C was detrimental to Seebeck coefficient. The thermoelectric transport properties can be tuned by varying the Co and Sn level. The lowest lattice thermal conductivity measured was 1.0 W m−1 K−1 for the Co level of 1.5. The Seebeck coefficient was positive for Co levels >0.8 and negative otherwise. Seebeck coefficients were low, ranging from −40 to 58 µV K−1. The combination of transmission electron microscopy with electron energy loss spectroscopy and powder X-ray diffraction established that Sn can substitute on 2a and 24g sites in the skutterudite structure. Due to the low Seebeck coefficients, the alloys exhibited low figure of merits (ZT) <0.05.
KeywordsSeebeck Coefficient Lattice Thermal Conductivity Total Thermal Conductivity NiSb Skutterudite Phase
The authors would like to thank Ben Kowalski, Tom Sabo, Serene Farmer, Ray Babuder, and Dereck Johnson from NASA Glenn Research Center and Case Western Reserve University for help with the experimental portion of this work. The authors would also like to thank Sabah Bux and Jean-Pierre Fleurial from NASA JPL for helpful discussions and assistance with hot pressing some samples. This research was supported in part by the Office of Basic Energy Sciences, Materials Sciences and Engineering Division, U.S. Department of Energy. Funding for this work was provided by funding source NASA/USRA 04555-004, the NASA Radioisotope Power System Program, and by NASA Kentucky under NASA Award No: NNX10AL96H.
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