Ralf Hassdorf

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.

Effect of Vacancies on the Thermoelectric Properties of Mg2Si containing Sb and Bi substitution

Mg 2 Si 1-x R x (R-Sb,Bi) compositions with x=0.025, 0.05 for Sb and x=0.01,0.025, 0.05 for Bi were synthesized by induction melting of the constituent elements followed by compaction by hot pressing. Phase identification by x-ray diffraction (XRD) indicate a biphasic nature for Bi substituted compositions for x≥.025 while solid solubility for the different Sb substitutions. Abundance distribution plots of the Seebeck (S) coefficient show asymmetry in the Sb compositions and is not observed in the Bi substituted samples. This indicates presence of vacancies only in the Sb substituted compositions. Electrical conductivity (σ), Seebeck coefficient (S) and thermal conductivity (κ) values were measured from 300K to 773 K. The observed trends in the absolute values of α and S can be explained based on doping/second phase influence in Bi substitutions and due to effect of vacancies for Sb substitutions. The (κ L ) (phonon component) values show a significant decrease for the Sb substitutions due to the presence of vacancies. Calculation of the thermoelectric figure of merit (ZT) show a ZT max of 0.56 for x=0.025 Bi composition compared to a ZT max of ∼ 0.05 for Mg 2 Si.