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Recent Advances in Nanostructured Thermoelectric Half-Heusler Compounds

View Article: PubMed Central - PubMed

ABSTRACT

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.

No MeSH data available.


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The lattice thermal conductivity of MSed Zr0.4Hf0.6NiSn0.98Sb0.02 nanocomposite and kmin of ZrNiSn estimated by applying a model developed by Cahill et al. [137]. The data is adopted from Reference [138].
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nanomaterials-02-00379-f022: The lattice thermal conductivity of MSed Zr0.4Hf0.6NiSn0.98Sb0.02 nanocomposite and kmin of ZrNiSn estimated by applying a model developed by Cahill et al. [137]. The data is adopted from Reference [138].

Mentions: One such question; is there still some ability to further reduce the lattice thermal conductivity by nanostructuring? In order to investigate just how much more further reduction of the lattice thermal conductivity are possible, then we need to estimate the minimum lattice thermal conductivity, κmin, for the specific materials. For example, κmin is estimated for the ZrNiSn compound by applying a model developed by Cahill et al. [137]:(3)where the summation is over the three polarization modes and kB the Boltzmann constant. The cut-off frequency (in unit of Kelvin) is , where na is the number density of atoms, the reduced Planck constant, vi the sound velocity for each polarization modes. The κmin of ZrNiSn, calculated by Zhu et al. [138], is shown in Figure 22, and thermal conductivity of ZrNiSn based nanocomposites are included for comparison. From this plot (Figure 22) it is apparent that there is still some opportunity of further significant reduction of κL between the κmin of ZrNiSn and the lowest κL of ZrNiSn based nanocomposites in the higher temperature range. Immediately, one might propose that nanostructures with even smaller sizes could further reduce the lattice thermal conductivity for a ZrNiSn based nanocomposite. However, the estimated phonon mean free path of HH-x nanocomposite is on the order of ~1 nm at high temperature [unpublished], which is comparable to the lattice parameter of the HH compound, so this approach is not likely to be effective. And, we should keep in mind that if the size of the HH matrix decreases to ~1 nm the effect of the small grains will also significantly decrease the carrier mobility through enhanced electron scattering [136]. Therefore, just blindly pursuing even smaller nanostructure is not likely to lead to the desired effect of enhancing the ZT but would most likely lead to a decrease in the ZT.


Recent Advances in Nanostructured Thermoelectric Half-Heusler Compounds
The lattice thermal conductivity of MSed Zr0.4Hf0.6NiSn0.98Sb0.02 nanocomposite and kmin of ZrNiSn estimated by applying a model developed by Cahill et al. [137]. The data is adopted from Reference [138].
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5304603&req=5

nanomaterials-02-00379-f022: The lattice thermal conductivity of MSed Zr0.4Hf0.6NiSn0.98Sb0.02 nanocomposite and kmin of ZrNiSn estimated by applying a model developed by Cahill et al. [137]. The data is adopted from Reference [138].
Mentions: One such question; is there still some ability to further reduce the lattice thermal conductivity by nanostructuring? In order to investigate just how much more further reduction of the lattice thermal conductivity are possible, then we need to estimate the minimum lattice thermal conductivity, κmin, for the specific materials. For example, κmin is estimated for the ZrNiSn compound by applying a model developed by Cahill et al. [137]:(3)where the summation is over the three polarization modes and kB the Boltzmann constant. The cut-off frequency (in unit of Kelvin) is , where na is the number density of atoms, the reduced Planck constant, vi the sound velocity for each polarization modes. The κmin of ZrNiSn, calculated by Zhu et al. [138], is shown in Figure 22, and thermal conductivity of ZrNiSn based nanocomposites are included for comparison. From this plot (Figure 22) it is apparent that there is still some opportunity of further significant reduction of κL between the κmin of ZrNiSn and the lowest κL of ZrNiSn based nanocomposites in the higher temperature range. Immediately, one might propose that nanostructures with even smaller sizes could further reduce the lattice thermal conductivity for a ZrNiSn based nanocomposite. However, the estimated phonon mean free path of HH-x nanocomposite is on the order of ~1 nm at high temperature [unpublished], which is comparable to the lattice parameter of the HH compound, so this approach is not likely to be effective. And, we should keep in mind that if the size of the HH matrix decreases to ~1 nm the effect of the small grains will also significantly decrease the carrier mobility through enhanced electron scattering [136]. Therefore, just blindly pursuing even smaller nanostructure is not likely to lead to the desired effect of enhancing the ZT but would most likely lead to a decrease in the ZT.

View Article: PubMed Central - PubMed

ABSTRACT

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.

No MeSH data available.


Related in: MedlinePlus