Nanocomposites to Enhance Zt in Thermoelectrics

Dresselhaus, M. S.; Chen, Gang; Ren, Zhifeng; Fleurial, Jean‐Pierre; Gogna, P.; Tang, Ming; Vashaee, Daryoosh; Lee, Hohyun; Wang, Xiaowei; Joshi, Giri; Zhu, Gaohua; Wang, Dezhi; Blair, Richard G.; Bux, Sabah K.; Kaner, Richard B.

doi:10.1557/proc-1044-u02-04

Cited by 30 publications

(22 citation statements)

References 20 publications

(17 reference statements)

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“…The most probable of these is the recent successful strategy of utilizing a nanostructuring approach in these materials. Nanostructuring has become a new paradigm approach of TE materials research that has been widely used to improve the ZT of several bulk TE materials over the past several years [92,93,94,95,96,97,98,99,100]. In the nanostructured bulk materials, or nanocomposites, the presence of multiple length-scales down to a few nanometers (), provides new avenues for phonon scattering in addition to the mass fluctuation alloying (), grain boundary or surface scattering (), phonon-phonon interactions (), and strain fields (), which all can occur in parallel and thus each adds to the process according to the Matthiessen’s rule, given below in Equation 2, with the shortest scattering process dominating.…”

Section: Structure Of Hh Compounds and Typical Strategies Of Enhanmentioning

confidence: 99%

Recent Advances in Nanostructured Thermoelectric Half-Heusler Compounds

et al. 2012

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Half-Heusler (HH) alloys have attracted considerable interest as promising thermoelectric (TE) materials in the temperature range around 700 K and above, which is close to the temperature range of most industrial waste heat sources. The past few years have seen nanostructuing play an important role in significantly enhancing the TE performance of several HH alloys. In this article, we briefly review the recent progress and advances in these HH nanocomposites. We begin by presenting the structure of HH alloys and the different strategies that have been utilized for improving the TE properties of HH alloys. Next, we review the details of HH nanocomposites as obtained by different techniques. Finally, the review closes by highlighting several promising strategies for further research directions in these very promising TE materials.

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Section: Structure Of Hh Compounds and Typical Strategies Of Enhanmentioning

confidence: 99%

Recent Advances in Nanostructured Thermoelectric Half-Heusler Compounds

et al. 2012

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“…54 Misalignment of crystallographic directions between adjacent grains can also lead to electron-scattering processes. 55 To obtain quantitative predictions of how grain boundaries affect the thermoelectric properties in nanocomposites using the Boltzmann equation, it is necessary to develop phonon and charge-carrier grain-boundary scattering models which give a grain-boundary scattering rate GB −1 . The resulting scattering rates can then be added to the bulk scattering rate and the thermoelectric properties calculated in the usual manner.…”

Section: Modeling Nanocompositesmentioning

confidence: 99%

Modeling study of thermoelectric SiGe nanocomposites

et al. 2009

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Nanocomposite thermoelectric materials have attracted much attention recently due to experimental demonstrations of improved thermoelectric properties over those of the corresponding bulk material. In order to better understand the reported data and to gain insight into transport in nanocomposites, we use the Boltzmann transport equation under the relaxation-time approximation to calculate the thermoelectric properties of n-type and p-type SiGe nanocomposites. We account for the strong grain-boundary scattering mechanism in nanocomposites using phonon and electron grain-boundary scattering models. The results from this analysis are in excellent agreement with recently reported measurements for the n-type nanocomposite but the experimental Seebeck coefficient for the p-type nanocomposite is approximately 25% higher than the model's prediction. The reason for this discrepancy is not clear at the present time and warrants further investigation. Using new mobility measurements and the model, we find that dopant precipitation is an important process in both n-type and p-type nanocomposites, in contrast to bulk SiGe, where dopant precipitation is most significant only in n-type materials. The model also shows that the potential barrier at the grain boundary required to explain the data is several times larger than the value estimated using the Poisson equation, indicating the presence of crystal defects in the material. This suggests that an improvement in mobility is possible by reducing the number of defects or reducing the number of trapping states at the grain boundaries.

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“…The main reason for the smaller ZT of p‐type SiGe material compared with n‐type SiGe is the smaller mobility of holes compared with electrons. Recently, there have been several studies to enhance the thermoelectric figure‐of‐merit of both n‐type and p‐type SiGe alloys 5–12. In almost all these works the enhancement in ZT has been shown by reducing the thermal conductivity via nanostructuring.…”

Section: Introductionmentioning

confidence: 99%

The effect of synthesis parameters on transport properties of nanostructured bulk thermoelectric p‐type silicon germanium alloy

Zamanipour

Shi

Dehkordi

et al. 2012

Physica Status Solidi (a)

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Nanostructured silicon germanium thermoelectric materials prepared by mechanical alloying and sintering method have recently shown large enhancement in figure‐of‐merit, ZT. The fabrication of these structures often involves many parameters whose understanding and precise control is required to attain large ZT. In order to find the optimum parameters for further enhancing the ZT of this material, we have grown and studied both experimentally and theoretically different nanostructured p‐type SiGe alloys. The effect of various parameters of milling process and sintering conditions on the thermoelectric properties of the grown samples were studied. The electrical and thermal properties were calculated using Boltzmann transport equation and were compared with the data of nanostructured and crystalline SiGe. It was found that the thermal conductivity not only depends on the average crystallite size in the bulk material, but also it is a strong function of alloying, porosity, and doping concentration. The Seebeck coefficient showed weak dependency on average crystallite size. The electrical conductivity changed strongly with synthesis parameters. Therefore, depending on the synthesis parameters the figure‐of‐merit reduced or increased by ∼60% compared with that of the crystalline SiGe. The model calculation showed that the lattice part of thermal conductivity in the nanostructured sample makes ∼80% of the total thermal conductivity. In addition, the model calculation showed that while the room temperature hole mean free path (MFP) in the nanostructured sample is dominated by the crystallite boundary scattering, at high temperature the MFP is dominated by acoustic phonon scattering. Therefore, the thermal conductivity can be further reduced by smaller crystallite size without significantly affecting the electrical conductivity in order to further enhance ZT.

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Nanocomposites to Enhance Zt in Thermoelectrics

Cited by 30 publications

References 20 publications

Recent Advances in Nanostructured Thermoelectric Half-Heusler Compounds

Recent Advances in Nanostructured Thermoelectric Half-Heusler Compounds

Modeling study of thermoelectric SiGe nanocomposites

The effect of synthesis parameters on transport properties of nanostructured bulk thermoelectric p‐type silicon germanium alloy

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