Effect of Nanostructuring on the Thermoelectric Properties of Co0.97Pd0.03Sb3

We synthesized n-type CeO₂/Co_0.97Pd_0.03Sb₃ composites with nanometric grain sizes (200 nm to 300 nm) by spark plasma sintering in order to promote phonon scattering at grain boundaries. Powdered samples were initially obtained by ball milling Co_0.97Pd_0.03Sb₃ together with x vol.% (x = 0, 0.5, 1, 2) of CeO₂ nanoparticles. This additive slows down the grain size growth of the skutterudite matrix which occurs during sintering, thereby contributing to phonon scattering. The nanostructured samples display reduced Hall electron concentration compared with that of the reference Co_0.97Pd_0.03Sb₃ because of Fe contamination by the steel balls and vials. However, the electronic transport properties are nearly identical to those of Co_0.98Pd_0.02Sb₃, which allows for comparison with this latter compound. The lattice thermal conductivity is strongly decreased in nano-Co_0.97Pd_0.03Sb₁₂ (?40% at 300 K). This results in an enhanced (+32%) ZT value peaking at 0.65 at 650 K in nano-Co_0.97Pd_0.03Sb₁₂ + 2% CeO₂ when compared with micro-Co_0.98Pd_0.02Sb₃.     

Thermoelectric properties and stability of glasses in the Cu‐As‐Te system

Chalcogenide glasses and more importantly their glass‐ceramics counterparts have been an interesting but very peculiar class of thermoelectric materials, with inherently low thermal conductivity (<0.3 W/m·K). In this study, we report on the fabrication of glasses in the ternary system Cu‐As‐Te (Cu_xAs_55?xTe₄₅ [5≤x≤20], Cu₁₅As_85?yTe_y [45≤y≤70], and Cu₂₀As_80?yTe_y [45≤y≤65]) by melt‐quenching and subsequent spark plasma sintering treatment. Their thermal and structural properties have been studied by differential scanning calorimetry and Raman spectroscopy, leading to give insights into the structural evolution of the glassy matrix. Coupling this information with the analysis of their electrical transport properties allowed us to deepen further our understanding of the compositional effect on their thermoelectric properties, and indirectly how the evolution of their electronic band structure is at play. Despite exhibiting low ZT values by themselves, Cu‐As‐Te glasses may still be interesting candidates for thermoelectricity through partial crystallization for which knowing the relationship between composition and properties remains essential.     

Oxidation Behavior of the Skutterudite Material Yb0.2Co4Sb12

Metallurgical and Materials Transactions A - The skutterudite materials belonging to the CoSb3 family are widely studied for thermoelectric applications. They are typically used under vacuum, but...     

Thermal Conductivity Reduction in CoSb<Subscript>3</Subscript>–CeO<Subscript>2</Subscript> Nanocomposites

CoSb₃ + x% CeO₂ nanocomposites (x = 1, 3, 5) were synthesized by ball-milling and spark plasma sintering. Scanning electron microscopy showed that some CeO₂ nano-inclusions sit at the boundaries of CoSb₃ grains. These inclusions also reduce the sizes of the CoSb₃ grains and crystallites by inhibiting their growth during sintering. Hall-effect measurements show that the CeO₂ inclusions modify the charge-carrier concentration in CoSb₃. The variations of the electrical resistivity for the 1% and 3% CeO₂ samples can at least partially be attributed to these modifications of the carrier concentration. Nonetheless, the resistivity increase in the 5% CeO₂ sample can unambiguously be ascribed to the presence of the CeO₂ inclusions. Thermal conductivity is systematically reduced (by more than 15% at 300 K) upon CeO₂ addition. Phonon diffusion by the increased number of CoSb₃ grain boundaries is one of the mechanisms involved in this reduction.     

Improved ZT in ball-milled and spark plasma sintered Cu15As30Te55 glass-ceramics

The influence of ball milling followed by Spark Plasma Sintering (SPS) on the thermoelectric properties of the Cu₁₅As₃₀Te₅₅ glass composition has been investigated by means of X-ray diffraction, scanning electron microscopy, and differential scanning calorimetry. The microstructure, composition, and thermal stability of the ball-milled samples before and after SPS have been correlated with the electrical and thermal transport properties. Upon ball milling, a glass-to-glass transformation is evidenced for short ball-milling times, followed by crystallization of the metastable β-As₂Te₃ phase within the glassy matrix. This glass-to-glass transformation favors the occurrence of the β-As₂Te₃ phase during the SPS process. A maximum figure of merit ZT of 0.29 at 400 K is obtained in the sample exhibiting the largest β-As₂Te₃ crystalline fraction. This ZT value is twice as high as the value obtained for the glass-ceramic sintered from non-ball-milled powder.     

Existence, structure and valence properties of the skutterudites CeyFe4−xCoxSb12

We report on sample preparation, annealing effects, electron microprobe analysis in the series Ce_yFe_4−xCo_xSb₁₂ which shows that a phase separation occurs for substituted samples (0<x<4) annealed at 650 and 550 °C. Single phase samples are obtained for either Ce_yFe₄Sb₁₂ or Ce_yCo₄Sb₁₂ samples annealed at 650 °C and for all compositions when annealed at 700 °C. The valence state of Ce in homogeneous samples has been studied using X-ray absorption spectroscopy (XAS). Ce ions are trivalent throughout the series and the XAS spectra does not show effect of the crystal field on the 5d-final state.