Anharmonicity and Effect of the Nanostructuring on the Lattice Dynamics of CrSi<sub>2</sub>

Moll, Adrien; Viennois, R.; Boehm, Martin; Koza, Michael Marek; Sidis, Y.; Rouquette, Jérôme; Laborde, S; Debray, Jérôme; Ménaert, Bertrand; Castellan, J. P.; Candolfi, Christophe; Lenoir, Bertrand; Hermet, Patrick; Beaudhuin, M.

doi:10.1021/acs.jpcc.1c02738

Cited by 7 publications

(6 citation statements)

References 35 publications

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“…The broadening of Raman bands could be explained by both the nanostructuration and the increase in defect contents in the crystal structure [28] induced during the mechanical milling. Moreover, this is characteristic of a lower relaxation time [29]. We consequently expect a lower thermal conductivity for nanostructured sample S2.…”

Section: Lattice Dynamic Of Bulk and Nanostructured β-Fesi2mentioning

confidence: 81%

Effect of Nanostructuring on the Thermoelectric Properties of β-FeSi2

et al. 2021

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Nanostructured β-FeSi2 and β-Fe0.95Co0.05Si2 specimens with a relative density of up to 95% were synthesized by combining a top-down approach and spark plasma sintering. The thermoelectric properties of a 50 nm crystallite size β-FeSi2 sample were compared to those of an annealed one, and for the former a strong decrease in lattice thermal conductivity and an upshift of the maximum Seebeck’s coefficient were shown, resulting in an improvement of the figure of merit by a factor of 1.7 at 670 K. For β-Fe0.95Co0.05Si2, one observes that the figure of merit is increased by a factor of 1.2 at 723 K between long time annealed and nanostructured samples mainly due to an increase in the phonon scattering and an increase in the point defects. This results in both a decrease in the thermal conductivity to 3.95 W/mK at 330 K and an increase in the power factor to 0.63 mW/mK2 at 723 K.

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Section: Lattice Dynamic Of Bulk and Nanostructured β-Fesi2mentioning

confidence: 81%

Effect of Nanostructuring on the Thermoelectric Properties of β-FeSi2

et al. 2021

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“…Although this class of materials presents intrinsically good electronic properties, their ZT remains lower (<0.4) than the state-of-theart materials due to relatively high thermal conductivities. In order to decrease κ, important research efforts leading to a significant improvement of the properties have been conducted recently mostly using strategies such as alloying [21], texturization [22], nanostructuration [23,24], or composite synthesis [25]. Despite the remarkable advances made on these materials, their integration into functional devices remains limited mostly because the realization of good-quality contacts is challenging and, thus, not well documented in the literature.…”

Section: Introductionmentioning

confidence: 99%

Fabrication and Evaluation of Low-Cost CrSi2 Thermoelectric Legs

et al. 2021

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CrSi2 is a promising thermoelectric material constituted of non-toxic and earth abundant elements that offer good perspectives for the mass production of inexpensive and reliable thermoelectric modules for waste heat recovery. Realization of robust metallic contacts with low electrical and thermal resistances on thermoelectric materials is crucial to maximize the conversion efficiency of such a device. In this article, the metallization of an undoped CrSi2 with Ti and Nb using a conventional Spark Plasma Sintering process is explored and discussed. These contact metals were selected because they have compatible thermal expansion coefficients with those of CrSi2, which were determined in this study by X-ray Diffraction in the temperature range 299–899 K. Ti was found to be a promising contact metal offering both strong adhesion on CrSi2 and negligible electrical contact resistance (<1 μΩ cm2). However, metallization with Nb resulted in the formation of cracks caused by large internal stress inside the sample during the fabrication process and the diffusion of Si in the metallic layer. A maximum conversion efficiency of 0.3% was measured for a sandwiched Ti/CrSi2/Ti thermoelectric leg placed inside a thermal gradient of 427 K. The preliminary results obtained and discussed in this article on a relatively simple case study aim to initiate the development of more reliable and efficient CrSi2 thermoelectric legs with an optimized design.

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“…However, the transition-metal (Ni/Cr)-derived 3 d states hybridize with the main group element (Si/Ge)-derived p states to form p–d bonding states, and the strength of the bonding depends on the virtual position of the p and d orbitals . The high γ E value calculated for the Cr–Si bond from the data obtained by EXAFS is corroborated by a recent investigation by Moll et al using DFT, which demonstrates strong anharmonicity by the Cr–Si bond in nanostructured CrSi 2 , where the optical phonon also contributes to the reduction of lattice thermal conductivity . In addition, the exceptional high γ E for the Cr–Ge bond can be attributed to the hybridization of the Cr 3 d orbital and the Ge 4 p orbital .…”

Section: Resultsmentioning

confidence: 60%

“…35 The high γ E value calculated for the Cr−Si bond from the data obtained by EXAFS is corroborated by a recent investigation by Moll et al using DFT, which demonstrates strong anharmonicity by the Cr−Si bond in nanostructured CrSi 2 , where the optical phonon also contributes to the reduction of lattice thermal conductivity. 53 In addition, the exceptional high γ E for the Cr−Ge bond can be attributed to the hybridization of the Cr 3d orbital and the Ge 4p orbital. 54 However, the nature of the hybridization is such that more number of unpaired electrons resides on Cr, which contributes to high magnetic moment and thus high anharmonicity and high electron−phonon scattering that is one of the cruxes in condensed matter physics.…”

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confidence: 99%

Potency of Extended X-ray Absorption Fine Structure Spectroscopy toward the Determination of Individual Bond Grüneisen Parameter for High Thermoelectric Performance

Basu

Nayak

Kumar

et al. 2023

ACS Appl. Energy Mater.

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Si–Ge is a well-known disordered alloy exhibiting high anharmonicity. These two features, disorder and anharmonicity, arise due to the unique nature of bonding instead of structural complexity and are beneficial as they limit the thermal conduction and are widely used in high-temperature thermoelectric applications. In this regard, a comprehensive understanding of the nature of interatomic bonds and the calculation of the Grüneisen parameter, which is a characteristic metric of anharmonicity, of the individual bond are essential to design a crystalline solid along with the development of a high-throughput thermoelectric alloy exhibiting ultralow lattice thermal conductivity. Here, we demonstrate the origin of the low lattice thermal conductivity, κl, of ∼0.8 and 0.4 Wm–1 K–1 for the transition-metal (Ni and Cr)-doped Si–Ge alloy, respectively, due to the difference in the anharmonic pair potential achieved using synchrotron-based X-ray absorption fine structure spectroscopy. The technique enables the determination of the Grüneisen parameter of the individual bond in the alloy and thus reveals the unpaired electron-induced bond anharmonicities and bonding heterogeneity. The technique also determines the bond Grüneisen parameter more precisely in comparison to the values obtained from the speed of sound, as the latter neglects the existence of the soft TO mode, which also contributes to lattice dynamics. Thus, the synergistic presence of (i) heteroatoms as point scatters (mass contrast), (ii) bonding anharmonicities, and (iii) electron–phonon scattering suppresses the lattice thermal conductivity beyond the theoretical alloy limit. Furthermore, the analysis imparts a conception for the estimation of the bond Grüneisen parameter through the acquisition and analysis of extended X-ray analysis of fine structure (EXAFS) spectra.

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Anharmonicity and Effect of the Nanostructuring on the Lattice Dynamics of CrSi₂

Cited by 7 publications

References 35 publications

Effect of Nanostructuring on the Thermoelectric Properties of β-FeSi2

Effect of Nanostructuring on the Thermoelectric Properties of β-FeSi2

Fabrication and Evaluation of Low-Cost CrSi2 Thermoelectric Legs

Potency of Extended X-ray Absorption Fine Structure Spectroscopy toward the Determination of Individual Bond Grüneisen Parameter for High Thermoelectric Performance

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Anharmonicity and Effect of the Nanostructuring on the Lattice Dynamics of CrSi2

Cited by 7 publications

References 35 publications

Effect of Nanostructuring on the Thermoelectric Properties of β-FeSi2

Effect of Nanostructuring on the Thermoelectric Properties of β-FeSi2

Fabrication and Evaluation of Low-Cost CrSi2 Thermoelectric Legs

Potency of Extended X-ray Absorption Fine Structure Spectroscopy toward the Determination of Individual Bond Grüneisen Parameter for High Thermoelectric Performance

Contact Info

Product

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Anharmonicity and Effect of the Nanostructuring on the Lattice Dynamics of CrSi₂