ICT2014 Abstracts

Nowadays, materials like skutterudites belong to the most promising thermoelectric materials; hence they are topical objects of research. Filled skutterudites EpT₄X₁₂ (Ep = alkaline, alkaline earth, lanthanide, actinoid atom, T = transition metal elements, and X = P, As, Sb, Ge) are materials which crystallize in a bcc-type structure. The basic skutterudite framework T₄X₁₂ provides cage-like voids, which can accommodate various guest atoms. These guest atoms are so called fillers or rattlers and show a lower binding energy as well as higher atomic displacement parameters in comparison to the other atoms in the framework. These fillers or rattlers are responsible for low thermal lattice conductivity and high mobilities, which has a positive influence to electrical conductivity and the figure of merit. Ge-based skutterudites like LaPt₄Ge₁₂ are p-type superconductors (holes are majority charge carriers), however exhibit thermoelectric properties. Partial substitution of Ge by Sb destroys superconductivity and leads to better thermoelectric properties which ends at the Zintl limit composition. Simple electron counting and DFT electronic structure calculations have shown that LaPt₄Ge_12-ySb_y with y > 5 should be n-type, but practical experience showed that no homogeneity region with y > 5 exist. For a better understanding of the evolution from superconductivity towards thermoelectricity in Ge-based skutterudites and the Zintl limits, substitutions of Pt by Ni (La_zPt_4-xNi_xGe_12-ySb_y) and Pd (La_zPt_4-xPd_xGe_12-ySb_y) were performed. The sample composition was analyzed by X-ray powder diffraction and by electron probe micro analysis. In order to characterise the fundamental behaviour and the thermoelectric abilities of this compounds, physical properties have been studied in a wide temperature range.