Exceptionally high thermoelectric figure of merit (zT>2), has been reported for (Ag1−ySbTe2)0.05(PbTe)0.95, which may involve the nanoscale microstructure. However, conflicting reports on the same materials claim only zT of 1 or less. Here we show that (Ag1−ySbTe2)0.05(PbTe)0.95 materials are multiphase on the scale of millimeters despite appearing homogeneous by x-ray diffraction and routine electron microscopy. Using a scanning Seebeck microprobe, we find significant variation of Seebeck coefficient (including both n-type and p-type behavior in the same sample) that can explain the discrepancy in reported zT. More homogeneous samples can be prepared with faster cooling rates.
We have developed a system for the simultaneous measurement of the electrical conductivity and the Seebeck coefficient for thermoelectric samples in the temperature region of 300 K to 1000 K. The system features flexibility in sample dimensions and easy sample exchange. In order to verify the accuracy of the setup we have referenced our system against the NIST standard reference material 3451 and other setups and can show good agreement. The developed system has been used in the search for a possible high temperature Seebeck standard material. FeSi2 emerges as a possible candidate as this material combines properties typical for thermoelectric materials with large scale fabrication, good spatial homogeneity, and thermal stability up to 1000 K.
Nano ZrO2/CoSb3 composites
with different ZrO2
contents were prepared using hot pressing. The phase purity, the microstructure
and the temperature-dependent transport parameters of the composites were
investigated. The dimensionless figure of merit (ZT) of 0.18 of the non-dispersed
CoSb3
preponderates the maximal value (0.17) of pure
CoSb3
reported in the literature, which is attributed to the prepared sample having higher
electrical conductivity due to the existence of a small amount of metallic Sb and lower
thermal conductivity due to the fine-grained structure. Compared to non-dispersed
CoSb3, a further improvement of 11% on ZT (0.20) was achieved in the composite with
0.05ZrO2
inclusions, which resulted from the enhanced ratio of electrical conductivity to thermal
conductivity and the Seebeck coefficient. The nanodispersion method provides
an effective approach to improving a material’s thermoelectric properties and
performance.
The properties of Co 4 Sb 12 with various In additions were studied. X-ray diffraction revealed the presence of the pure d-phase of In 0.16 Co 4 Sb 12 , whereas impurity phases (c-CoSb 2 and InSb) appeared for x = 0.25, 0.40, 0.80, and 1.20. The homogeneity and morphology of the samples were observed by Seebeck microprobe and scanning electron microscopy, respectively. All the quenched ingots from which the studied samples were cut were inhomogeneous in the axial direction. The temperature dependence of the Seebeck coefficient (S), electrical conductivity (r), and thermal conductivity (j) was measured from room temperature up to 673 K. The Seebeck coefficient of all In-added Co 4 Sb 12 materials was negative. When the filler concentration increases, the Seebeck coefficient decreases. The samples with In additions above the filling limit (x = 0.22) show an even lower Seebeck coefficient due to the formation of secondary phases: InSb and CoSb 2 . The temperature variation of the electrical conductivity is semiconductor-like. The thermal conductivity of all the samples decreases with temperature. The central region of the In 0.4 Co 4 Sb 12 ingot shows the lowest thermal conductivity, probably due to the combined effect of (a) rattling due to maximum filling and (b) the presence of a small amount of fine-dispersed secondary phases at the grain boundaries. Thus, regardless of the non-single-phase morphology, a promising ZT (S 2 rT/j) value of 0.96 at 673 K has been obtained with an In addition above the filling limit.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.