An official website of the United States government
Thermoelectric materials could play a crucial role in the future of wearable electronic devices. They can continuously generate electricity from body heat. For efficient operation in wearable systems, in addition to a high thermoelectric figure of merit, zT, the thermoelectric material must have low thermal conductivity and a high Seebeck coefficient. In this study, we successfully synthesized high-performance nanocomposites of n-type Bi2Te2.7Se0.3, optimized especially for body heat harvesting and power generation applications. Different techniques such as dopant optimization, glass inclusion, microwave radiation in a single mode microwave cavity, and sintering conditions were used to optimize the temperature-dependent thermoelectric properties of Bi2Te2.7Se0.3. The effects of these techniques were studied and compared with each other. A room temperature thermal conductivity as low as 0.65 W/mK and high Seebeck coefficient of −297 μV/K were obtained for a wearable application, while maintaining a high thermoelectric figure of merit, zT, of 0.87 and an average zT of 0.82 over the entire temperature range of 25 °C to 225 °C, which makes the material appropriate for a variety of power generation applications.
more »
« less
Thermoelectric Properties of Scandium Sesquitelluride
Rare-earth (RE) tellurides have been studied extensively for use in high-temperature thermoelectric applications. Specifically, lanthanum and praseodymium-based compounds with the Th3P4 structure type have demonstrated dimensionless thermoelectric figures of merit (zT) up to 1.7 at 1200 K. Scandium, while not part of the lanthanide series, is considered a RE element due to its chemical similarity. However, little is known about the thermoelectric properties of the tellurides of scandium. Here, we synthesized scandium sesquitelluride (Sc2Te3) using a mechanochemical approach and formed sintered compacts through spark plasma sintering (SPS). Temperature-dependent thermoelectric properties were measured from 300–1100 K. Sc2Te3 exhibited a peak zT = 0.3 over the broad range of 500–750 K due to an appreciable power factor and low-lattice thermal conductivity in the mid-temperature range.
more »
« less
- Award ID(s):
- 1709158
- PAR ID:
- 10110347
- Date Published:
- Journal Name:
- Materials
- Volume:
- 12
- Issue:
- 5
- ISSN:
- 1996-1944
- Page Range / eLocation ID:
- 734
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Compositional diversity and intriguing structural features have made Zintl phases excellent candidates as thermoelectric materials. Zintl phase with 21-4-18 composition has shown high thermoelectric performance in the mid- to high-temperature ranges. The complex crystal structure and favorable transport properties of these compounds indicate the potential for high thermoelectric efficiency. Arsenic-based Eu21Zn4As18, belonging to the Ca21Mn4Sb18 structure type, exhibits a semiconductor-like p-type transport behavior and has a calculated band gap of 0.49 eV. The compound is paramagnetic at high temperatures, with an antiferromagnetic transition occurring at T-N = similar to 10 K. The moment obtained from the Curie-Weiss data fit aligns with Eu2+ ions. At the same time, the field-dependent measurement at 2 K indicates complex magnetic ordering with a saturation moment consistent with Eu2+ ions. Pristine Eu21Zn4As18 exhibits an ultralow lattice thermal conductivity of 0.40 W m(-1) K-1 at 873 K. Electronic transport properties measurement shows evidence of bipolar conduction across much of the measured temperature range (450-780 K). However, the Seebeck coefficient remains extremely high (>440 mu V K-1) across this range, indicating the potential for high zT if an appropriate dopant is found. This work represents the first report on the temperature-dependent thermal conductivity, Seebeck coefficient, and thermoelectric efficiency of the arsenic-containing Zintl phase with 21-4-18 composition, showcasing its promise for further optimization of the thermoelectric performance.more » « less
-
This work evaluates wearable thermoelectric (TE) devices consisting of nanocomposite thermoelectric materials, aluminum nitride ceramic headers, and a flexible and stretchable circuit board. These types of wearable systems are part of a broader effort to harvest thermal energy from the body and convert it into electrical energy to power wearable electronics. Thermoelectric generators are made of p-type (Bi,Sb)2Te3 and n-type Bi2(Te,Se)3. The nanocomposite thermoelectric materials investigated in this research address the two fundamental challenges for body heat harvesting. The first challenge is related to the unavailability of high zT n-type materials near the body temperature. The second challenge is related to the thermoelectric power factor. To improve the zT, one has to increase the power factor simultaneously while reducing the thermal conductivity. Our nanocomposites result in enhancement of the TE power factor along with the reduction of the thermal conductivity. The fundamental reason is a nanoscale effect that happens only when the energy distribution function of the carriers does not relax to that of the bulk material in the crystallites. Ten p-type and ten n-type nanocomposite ingots were synthesized and characterized in this research. All ingots were characterized versus their thermoelectric properties and they all showed similarly enhanced properties. Our nanocomposites, compared to commercial materials, have better zT and thermal resistivity by 40% and 75% for p-type, respectively, and 15% and 140% for n-type. Compared to the state-of-the-art materials, our nanocomposites produce significantly higher power due to their optimized properties for the body temperature.more » « less
-
Thermoelectric materials can convert heat into electricity. They are used to generate electricity when other power sources are not available or to increase energy efficiency by recycling waste heat. The Yb 21 Mn 4 Sb 18 phase was previously shown to have good thermoelectric performance due to its large Seebeck coefficient (∼290 μV K −1 ) and low thermal conductivity (0.4 W m −1 K −1 ). These characteristics stem respectively from the unique [Mn 4 Sb 10 ] 22− subunit and the large unit cell/site disorder inherent in this phase. The solid solutions, Yb 21 Mn 4− x Cd x Sb 18 ( x = 0, 0.5, 1.0, 1.5) and Yb 21− y Ca y Mn 4 Sb 18 ( y = 3, 6, 9, 10.5) have been prepared, their structures characterized and thermoelectric properties from room temperature to 800 K measured. A detailed look into the structural disorder for the Cd and Ca solid solutions was performed using synchrotron powder X-ray diffraction and pair distribution function methods and shows that these are highly disordered structures. The substitution of Cd gives rise to more metallic behavior whereas Ca substitution results in high resistivity. As both Cd and Ca are isoelectronic substitutions, the changes in properties are attributed to changes in the electronic structure. Both solid solutions show that the thermal conductivities remain extremely low (∼0.4 W m −1 K −1 ) and that the Seebeck coefficients remain high (>200 μV K −1 ). The temperature dependence of the carrier mobility with increased Ca substitution, changing from approximately T −1 to T −0.5 , suggests that another scattering mechanism is being introduced. As the bonding changes from polar covalent with Yb to ionic for Ca, polar optical phonon scattering becomes the dominant mechanism. Experimental studies of the Cd solid solutions result in a max zT of ∼1 at 800 K and, more importantly for application purposes, a ZT avg ∼ 0.6 from 300 K to 800 K.more » « less
-
GeTe-based alloys hold great promise for thermoelectric applications. Our comprehensive study investigates the intricate interplay between chemical bonding and transport properties in cubic GeTe. We demonstrate a balance between minimizing thermal conductivity and maximizing power factor, guided by the mediating influence of chemical bonding. Our primary findings reveal that Pb-doped GeTe exhibits low lattice thermal conductivity due to weak p–p orbital interactions, whereas In-doping boosts lattice thermal conductivity by reinforcing the chemical bonds, as elucidated by crystal orbital hamilton population (COHP) analysis. Further investigation reveals weak s–p interactions in Bi-, Sb-, and Pb-doped GeTe, and strong s–p interactions in In-doped GeTe compared to the pure GeTe, as probed by projected density of state (PDOS). These dual effects explain the experimentally observed high power factor and enhanced zT in Bi-, Sb-, and Pb- doping in contrast to In-doping. In our study, we find that weak s–p interactions improves electronic performance by modifying DOS whereas weak p–p interactions reduce thermal transport by diminishing the strength of chemical bonding. These findings underscore the correlation between doping-induced modifications in chemical bonding and resulting thermoelectric properties. Utilizing a first-principles framework, we systematically explore the temperature and carrier concentration-dependent transport properties of pure GeTe under relaxation time approximation. Optimization strategies yield a maximum peak power factor times temperature of 2.2 Wm−1 K−1 and a maximum zT value of ∼0.83 at 800 K, showcasing the potential for tailored thermoelectric performance. Finally, this research presents a systematic approach to improve thermoelectric performance by modifying chemical bonds through doping.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.3390/ma12050734
