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G. Rogl, A. Grytsiv, F. Failamani, M. Hochenhofer, E. Bauer, P. Rogl:
"Attempts to further enhance ZT in skutterudites via nano-composites";
Journal of Alloys and Compounds, 695 (2017), S. 682 - 696.

Skutterudites are known as excellent thermoelectric p- and n-type materials and have already achieved
good efficiencies for the conversion of heat to electricity, but nevertheless researchers try to further
enhance the figure of merit, ZT. In the present work the aim was to mix p- and n-type skutterudite
powders with additives in order to produce an evenly dispersed distribution of sub micron grains,
preferable small nano-particles, which enhance the scattering of the heat carrying phonons of different
wavelengths and reduce thermal conductivity without changing electrical resistivity and Seebeck coefficient.
Various quantities of three groups of materials (a) nonmetallic oxides (Al2O3), (b) metallic oxides
(Cu2O and La1.85Sr0.15CuO4) and (c) metallic borides (Fe2.25Co0.75B and Ta0.8Zr0.2B) were added to
industrially produced p-type (DDyFe3CoSb12) and n-type ((Mm,Sm)yCo4Sb12) skutterudite powders. First
the influence of pre-sieving and various ball milling conditions before hot pressing were studied, using
Al2O3 as additive. As a consequence of these studies pre-sieved powders and high-energy ball milling
were used for all following experiments. The goal, to enhance ZT was not reached with Al2O3 and Cu2O.
La1.85Sr0.15CuO4 was successful for the n-type, Fe2.25Co0.75B for the p-type skutterudites, although ZTenhancement
was small, but with Fe2.25Co0.75B the maximum ZT could be shifted to lower temperatures,
a valuable information for device production. Much better results in respect to ZT values were
gained with adding 0.5, 1.0 and 1.5 wt.% Ta0.8Zr0.2B to p-type DDyFe3CoSb12. In this series it was possible
to enhance ZT (from ZT ~ 1.2 to ZT ~ 1.3) as well as to significantly increase the thermal-electrical
conversion efficiency h. In addition, we found that all boride additives enhanced the hardness, elastic
moduli and fracture resistance.

Thermoelectric materials Nanostructured Mechanical properties Scanning electron microscopy SEM

http://dx.doi.org/10.1016/j.jallcom.2016.10.114