Charge carrier transport and corresponding thermoelectric properties are often affected by several parameters, necessitating a thorough comparative study for a profound understanding of the detailed conduction mechanism. Here, as a model system, we compare the electronic transport properties of two layered semiconductors, Sb 2 Si 2 Te 6 and Bi 2 Si 2 Te 6 . Both materials have similar grain sizes and morphologies, yet their conduction characteristics are significantly different. We found that phase boundary scattering can be one of the main factors for Bi 2 Si 2 Te 6 to experience significant charge carrier scattering, whereas Sb 2 Si 2 Te 6 is relatively unaffected by the phenomenon. Furthermore, extensive point defect scattering in Sb 2 Si 2 Te 6 significantly reduces its lattice thermal conductivity and results in high zT values across a broad temperature range. These findings provide novel insights into electron transport within these materials and should lead to strategies for further improving their thermoelectric performance.

In this study we report a combined theoretical and experimental work on the tellurium doping of thermoelectric ZnSb. We investigated the influence of tellurium on the phase's stabilities by density functional theory (DFT) calculations. During experimental validation by means of SEM and EPMA characterization "needlelike" areas of Te-doped ZnSb were identified. The experimental results also highlight that for the compositions Zn 0.5 Sb 0.5-x Te x (x=0.001, 0.05, 0.1) the system reaches a non-equilibrium state where ZnSb, ZnTe and Te-doped ZnSb are simultaneously present. The determination of the doping mechanism has demonstrated the formation of Te-doped Zn 4 Sb 3 after quenching, leading to the formation of Te-doped ZnSb due to the zinc diffusion during annealing. Presumed from experimental observation oxygen prevents the tellurium diffusion, which was confirmed by DFT calculations. These results lead to the conclusion of an inert processing chain as a necessary prerequisite for production of n-type ZnSb, which puts hurdles on a cheap and easily scalable tellurium doping for homogeneous and competitive products.

The target of this study is to evaluate the suitability of a contact scheme designed for thermoelectric characterization of FeSi 2 -based materials with the combined thermoelectric measurement (CTEM) technique. A Fe 0.95 Co 0.05 Si 2 sample is mounted between the CTEM sample holder blocks made of molybdenum using Field's metal solder. The electrical contact resistance is monitored under thermal cycling up to 580 °C by an in-house built contact resistance in situ monitoring facility. After cycling, the microstructure was studied by scanning electron microscopy and energy-dispersive X-ray spectroscopy on the cross section of the contact zone. For the developed preparation process, the specific contact resistance was found suitably low up to 415 °C (<200 μΩ• cm 2 which is less than 10% of the sample resistance). Above 415 °C, oxidation degrades the electrical contact irreversibly.

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