Andreas Sesselmann

Structural and Thermoelectric Properties of Bi1−xSbx Nanoalloys Prepared by Mechanical Alloying

Bi1−xSbx nanoparticles were prepared by mechanical alloying and compacted using different techniques. The influence of the composition as well as the pressing conditions on the thermoelectric performance was investigated. A strong dependence of the thermoelectric properties on the composition was found, which deviates from the behavior of single crystals. The results indicate a significant change in the band structure of the material induced by the reduced size. The influence of the pressing conditions on the thermoelectric properties also showed composition dependence. The results show that the compacting method has to be chosen carefully.

High-Temperature Transport Properties of Indium Added Cobalt-Antimonide Based Skutterudites Processed by Current Assisted Short-Term Sintering

For more than a decade, skutterudites such as cobalt antimonides have been widely studied as a promising thermoelectric (TE) material for high-temperature applications. High thermoelectric figure of merit (ZT) in this material system can be achieved by suitable doping or by filling the interstitial voids with guest atoms. One of the best improvements in ZT is reported when indium (In) is used as additive to cobalt-antimonide skutterudites, as has been done in this study. Compaction of the grinded powders was carried out by a current-assisted short-term sintering device, which significantly reduces the process time in comparison to conventional hot pressing. Phase homogeneity of the bulk material has been probed by X-ray powder diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX). TE properties (i.e. electrical conductivity, Seebeck coefficient and thermal conductivity) have been analyzed in the temperature range from 300 K to 700 K. The functional homogeneity of the samples was screened by the Potential & Seebeck Microprobe (PSM). Adapted from these results the effect of indium addition to short-term sintered cobalt-antimonide based skutterudites with absence of impurity phases will be discussed.

The Influence of Synthesis Procedure on the Microstructure and Thermoelectric Properties of p-Type Skutterudite Ce0.6Fe2Co2Sb12

We have investigated p-type skutterudite samples with the nominal composition Ce0.6Co2Fe2Sb12 synthesized from elementary constituents by gas atomization and conventional melting, and also those synthesized from ternary and binary phases such as FexCo1−xSb2 and CeSb2, respectively, which were mixed and subsequently ball-milled. We conducted measurements of the temperature-dependent transport properties (Seebeck coefficient, thermal/electrical conductivity) and carried out scanning electron microscope analysis, electron probe micro-analysis and powder x-ray diffraction to obtain information about microstructure and elementary distribution of the phases. We show that the presented synthesis methods each possess particular strengths but ultimately, however, lead to different final compositions of the skutterudite phase and secondary phases, which significantly influence the thermoelectric properties of the material. Material prepared using an educt method gave the best thermoelectric properties with a peak ZT of 0.7. Furthermore, we show that even an apparent homogeneous skutterudite area within the material exhibits varying stoichiometry in each grain even though they conform to the solubility range of cerium in this p-type skutterudite. Moreover, we show that marcasite is preferred as an educt over the arsenopyrite phase and discuss the formation of the p-type skutterudite phase with these synthesis techniques.