▪ Abstract Recently there has been a resurgence of research efforts related to the investigation of new and novel materials for small-scale thermoelectric refrigeration and power generation applications. These materials need to couple and optimize a variety of properties in order to exhibit the necessary figure of merit, i.e. the numerical expression that is commonly used to compare one potential thermoelectric material with another. The figure of merit is related to the coefficient of performance or efficiency of a particular device made from a material. The best thermoelectric material should possess thermal properties similar to that of a glass and electrical properties similar to that of a perfect single-crystal material, i.e. a poor thermal conductor and a good electrical conductor. Skutterudites are materials that appear to have the potential to fulfill such criteria. These materials exhibit many types of interesting properties. For example, skutterudites are members of a family of compounds we call...

SKUTTERUDITES : A phonon-glass-electron crystal approach to advanced thermoelectric energy conversion applications

Thermoelectric (Peltier) heat pumps are capable of refrigerating solid or fluid objects, and unlike conventional vapor compressor systems, they can be miniaturized without loss of efficiency. More efficient thermoelectric materials need to be identified, especially for low-temperature applications in electronics and devices. The material CsBi(4)Te(6) has been synthesized and its properties have been studied. When doped appropriately, it exhibits a high thermoelectric figure of merit below room temperature (ZT(max) approximately 0.8 at 225 kelvin). At cryogenic temperatures, the thermoelectric properties of CsBi(4)Te(6) appear to match or exceed those of Bi(2-x)Sb(x)Te(3-y)Se(y) alloys.

https://science.sciencemag.org/content/sci/287/5455/1024.full.pdf

CsBi4Te6: A High-Performance Thermoelectric Material for Low-Temperature Applications

This review highlights the recent progress made in the area of thermoelectric (TE) applications of conducting polymers and related composites. Several examples of such materials and their TE properties are discussed. TE properties of new poly(2,7-carbazole) derivatives are highlighted. References are also made to carbon nanotube/polymer composites and their improved electrical and TE performance. Studies on polymer/inorganic materials composites have also taken a step forward and have shown very promising TE properties. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

https://onlinelibrary.wiley.com/doi/pdf/10.1002/polb.22206

Conducting polymers: Efficient thermoelectric materials

Research in topological matter has expanded to include the Dirac and Weyl semimetals1–10, which feature three-dimensional Dirac states protected by symmetry. Zirconium pentatelluride has been of recent interest as a potential Dirac or Weyl semimetal material. Here, we report the results of experiments performed by in situ three-dimensional double-axis rotation to extract the full 4π solid angular dependence of the transport properties. A clear anomalous Hall effect is detected in every sample studied, with no magnetic ordering observed in the system to the experimental sensitivity of torque magnetometry. Large anomalous Hall signals develop when the magnetic field is rotated in the plane of the stacked quasi-two-dimensional layers, with the values vanishing above about 60 K, where the negative longitudinal magnetoresistance also disappears. This suggests a close relation in their origins, which we attribute to the Berry curvature generated by the Weyl nodes. Magnetotransport measurements show that ZrTe5 exhibits an anomalous Hall effect without magnetic ordering, a signature of Berry curvature introduced by Weyl nodes. This indicates that ZrTe5 may be a Weyl semimetal, even though this was not predicted.

/pdf/anomalous-hall-effect-in-zrte-5-4dvlpspa2g.pdf

Anomalous Hall effect in ZrTe 5

A series of alternating poly(2,7-carbazole) derivatives have been synthesized. The evaluation of their thermoelectric properties in doped films revealed high electrical conductivity (up to 500 S/cm) and a relatively high Seebeck coefficient (up to 70 μV/K). The best compromise between these two thermoelectric parameters led to a maximum value of 19 μW m−1 K−2 as the power factor. As observed from X-ray analyses, it has been observed that the high electrical conductivity was obtained with structured polymers. Good air stability was also observed with these thermoelectric polymers.

Electrical and Thermoelectric Properties of Poly(2,7-Carbazole) Derivatives

The thermoelectric properties (resistivity and thermopower) of single crystals of the low dimensional pentatelluride materials, HfTe5  and ZrTe5, have been measured as a function of temperature from 10 K<T<320 K. The effect of small amounts of Ti substitutional doping (M1−xTixTe5, where M=Hf, Zr) on the thermoelectric properties is reported here. A resistive transition occurs in the pentatellurides, as evidenced by a peak in the resistivity, TP≈80 K for HfTe5 and TP≈145 K for ZrTe5. Both parent materials exhibit a large positive (p-type) thermopower near room temperature which undergoes a change to negative (n-type) below the peak temperature. The thermal conductivity is relatively low (≈5 W/m K) for the MTe5 materials. The Ti substitution affects the electronic properties strongly, producing a substantial shift in the peak temperature while the large values of thermopower remain essentially unaffected. These results warrant further investigation of these materials as candidates for low temperature thermo...

Effect of Ti substitution on the thermoelectric properties of the pentatelluride materials M1−xTixTe5 (M=Hf, Zr)

We have measured the resistivity of (Bi,Pb${)}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{\mathit{n}\mathrm{\ensuremath{-}}1}$${\mathrm{Cu}}_{\mathit{n}}$${\mathrm{O}}_{\mathit{x}}$ single-crystal whiskers in the a and c directions. Our results indicate that the whiskers may be either 2:2:1:2 (n=1) or 2:2:2:3 (n=2) or have both phases present. Well above ${\mathit{T}}_{\mathit{c}}$, the resistivity in the a direction decreases linearly with temperature. We also studied the paraconductivity due to thermal fluctuations above ${\mathit{T}}_{\mathit{c}}$. The paraconductivity in the a direction shows quasi-one-dimensional behavior for temperatures close to ${\mathit{T}}_{\mathit{c}}$. This quasi-one-dimensional behavior may be due to a percolative conduction path. For the c direction, the resistivity is best fit by ${\mathrm{\ensuremath{\rho}}}_{\mathit{c}}$=${\mathit{Ae}}_{\mathit{g}}^{\mathrm{\ensuremath{-}}\mathit{E}}$/kT, where T is the temperature. However, as T approaches ${\mathit{T}}_{\mathit{c}}$ from above, ${\mathrm{\ensuremath{\rho}}}_{\mathit{c}}$ increases much faster than a thermally activated law, perhaps because of the fluctuations.

Conductivity and paraconductivity in (Bi,Pb)2Sr2Can-1CunOx whiskers.

We have measured the stress-strain properties of whiskerlike samples of the high-T c material Bi 2 Sr 2 CaCu 2 O x . We observe an anomalous temperature dependence of Young's modulus (Y) around 300 K. The magnitude of Y falls by a factor of 3-4 between 270 and 330 K. We also observe hysteresis in the stress-strain curves in this same temperature range. The stress and strain relax toward the middle of the hysteresis loop with a characteristic time of approximately 20 sec. All these phenomena are reproducible as either the stress or temperature is cycled

Evidence in the elastic properties for a stress-related phase transition in the high-Tc material: Bi2Sr2CaCu2Ox.

We have measured Young's modulus in ribbon-like whisker samples of the high- T c materials: Bi 2 Sr 2 CaCu 2 O x and Bi 2 Sr 2 Ca 2 Cu 3 O x . This is the first direct measurement of Young's modulus for whiskers of any of the high T c materials. We used a stress-strain probe that applies an axial force (uniaxial stress) to the whisker-like sample and simultaneously measures the corresponding sample elongation. The slope of the resulting stress-strain curve yields the magnitude of Young's modulus ( Y ). We found these Bi based high- T c materials to be soft with Y ≈20 GPa for Bi 2 Sr 2 CaCu 2 O x and Y ≈25 GPa for Bi 2 Sr 2 Ca 2 Cu 3 O x .

M. Marone

Papers

Effect of Ti substitution on the thermoelectric properties of the pentatelluride materials M1−xTixTe5 (M=Hf, Zr)

Conductivity and paraconductivity in (Bi,Pb)2Sr2Can-1CunOx whiskers.

Evidence in the elastic properties for a stress-related phase transition in the high-Tc material: Bi2Sr2CaCu2Ox.

Measure of the magnitude of Young's modulus in whisker-like samples of the Bi-based high-Tc materials Bi2Sr2CaCu2Ox and Bi2Sr2Ca2Cu3Ox