Thermoelectric properties of single crystalline Ba8AlxSi46-xclathrate by using flux Czochralski method

Nagatomo, Yuya; Mugita, Naoki; Nakakohara, Yusuke; Saisho, Makoto; Tajiri, Mikihito; Teranishi, Ryo; Munetoh, Shinji

doi:10.1088/1742-6596/379/1/012008

Cited by 13 publications

(10 citation statements)

References 25 publications

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“…According to experimental, [49][50][51]57,[62][63][64][65][66][67] theoretical 22,68 as well as combined 53,69 studies, the structural and physical properties of, ternary, inorganic clathrates vary markedly with chemical composition. Specifically, it has been shown that the displacement of the guest atom from the 6d site 22,51 and the associated vibrational frequencies 57,62 depend on the number of Al or Ga atoms per unit cell, in ternary compounds of the type Ba 8 {Al,Ga} x {Si,Ge} 46−x .…”

Section: Chemical Composition and Orderingmentioning

confidence: 99%

Thermal conductivity in intermetallic clathrates: A first-principles perspective

et al. 2019

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Inorganic clathrates such as Ba8GaxGe46−x and Ba8GaxSi46−x commonly exhibit very low thermal conductivities. A quantitative computational description of this important property has proven difficult, in part due to the large unit cell, the role of disorder, and the fact that both electronic carriers and phonons contribute to transport. Here, we conduct a systematic analysis of the temperature and composition dependence of low-frequency modes associated with guest species in Ba8GaxGe46−x and Ba8AlxSi46−x ("rattler modes"), as well as of thermal transport in stoichiometric Ba8Ga16Ge30. To this end, we account for phonon-phonon interactions by means of temperature dependent effective interatomic force constants (TDIFCs), which we find to be crucial in order to achieve an accurate description of the lattice part of the thermal conductivity. While the analysis of the thermal conductivity is often largely focused on the rattler modes, here, it is shown that at room temperatures modes with ω 10 meV account for 50% of lattice heat transport. Finally, the electronic contribution to the thermal conductivity is computed, which shows the Wiedemann-Franz law to be only approximately fulfilled. As a result, it is crucial to employ the correct prefactor when separating electronic and lattice contributions for experimental data. arXiv:1807.01502v2 [cond-mat.mtrl-sci]

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Section: Chemical Composition and Orderingmentioning

confidence: 99%

Thermal conductivity in intermetallic clathrates: A first-principles perspective

et al. 2019

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“…The variety of chemical elements available for building the clathrate structure offers a wide compositional space for optimizing their electronic properties and reaching high efficiency. , Clathrates based on Ge and Ga have demonstrated good performance in their thermoelectric properties, e.g., in terms of a glass-like thermal conductivity of Sr 8 Ga 16 Ge 30 , and high thermoelectric efficiency of Ba 8 Ga 16 Ge 30 . , Al–Si-based clathrates are of technological interest in terms of price, weight, and low environmental impact. ,− So far, they could be synthesized in the range x ≤ 15 for Ba 8 Al x Si 46– x , , and only for x = 10 in the case of Sr 8 Al x Si 46– x . (The slightly higher electronegativity of Sr as compared to Ba may lead to a lower solubility of Al in Sr-filled clathrates.)…”

Section: Introductionmentioning

confidence: 99%

Predicting Ground-State Configurations and Electronic Properties of the Thermoelectric Clathrates Ba₈Al_xSi_46–xand Sr₈Al_xSi_46–x

2017

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The structural and electronic properties of the clathrate compounds Ba 8 Al x Si 46−x and Sr 8 Al x Si 46−x are studied from first-principles, considering an Al content x between 6 and 16. Due to the large number of possible substitutional configurations, we make use of a special iterative clusterexpansion approach, to predict ground states and quasidegenerate structures in a highly efficient way. These are found from a simulated annealing technique where millions of configurations are sampled. For both compounds, we find a linear increase of the lattice constant with the number of Al substituents, confirming experimental observations for Ba 8 Al x Si 46−x . Also the calculated bond distances between high-symmetry sites agree well with experiment for the full compositional range. For x being below 16, all configurations are metallic for both materials. At the charge-balanced composition (x = 16), the substitutional ordering leads to a metal−semiconductor transition, and the ground states of Ba 8 Al 16 Si 30 and Sr 8 Al 16 Si 30 exhibit indirect Kohn−Sham band gaps of 0.36 and 0.30 eV, respectively, while configurations higher in energy are metals. The finding of semiconducting behavior is a promising result in view of exploiting these materials in thermoelectric applications.

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“…The Ga-containing as-grown crystal shows compositional gradients as seen in other crystals prepared by the floating-zone technique. [26][27][28][29][30][31][32] This can be exploited to study the compositional dependence of the TE properties. Interestingly, in a very narrow composition range, the charge carrier mobility is sizably enhanced with increasing Ga content, leading to reduced…”

Section: Introductionmentioning

confidence: 99%

Suppression of vacancies boosts thermoelectric performance in type-I clathrates

et al. 2018

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Intermetallic type-I clathrates continue to attract attention as promising thermoelectric materials. Here we present structural and thermoelectric properties of single crystalline Ba 8 (Cu,Ga,Ge,2) 46 , where 2 denotes a vacancy. By single crystal X-ray diffraction on crystals without Ga we find clear evidence for the presence of vacancies at the 6c site in the structure. With increasing Ga content, vacancies are successively filled. This increases the charge carrier mobility strongly, even within a small range of Ga substitution, leading to reduced electrical resistivity and enhanced thermoelectric performance. The largest figure of merit ZT = 0.9 at 900 K is found for a single crystal of approximate composition Ba 8 Cu 4.6 Ga 1.0 Ge 40.4 . This value, that may further increase at higher temperatures, is one of the largest to date found in transition metal element-based clathrates.

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Thermoelectric properties of single crystalline Ba₈Al_xSi_46-xclathrate by using flux Czochralski method

Cited by 13 publications

References 25 publications

Thermal conductivity in intermetallic clathrates: A first-principles perspective

Thermal conductivity in intermetallic clathrates: A first-principles perspective

Predicting Ground-State Configurations and Electronic Properties of the Thermoelectric Clathrates Ba₈Al_xSi_46–xand Sr₈Al_xSi_46–x

Suppression of vacancies boosts thermoelectric performance in type-I clathrates

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Thermoelectric properties of single crystalline Ba8AlxSi46-xclathrate by using flux Czochralski method

Cited by 13 publications

References 25 publications

Thermal conductivity in intermetallic clathrates: A first-principles perspective

Thermal conductivity in intermetallic clathrates: A first-principles perspective

Predicting Ground-State Configurations and Electronic Properties of the Thermoelectric Clathrates Ba8AlxSi46–xand Sr8AlxSi46–x

Suppression of vacancies boosts thermoelectric performance in type-I clathrates

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Product

Resources

About

Thermoelectric properties of single crystalline Ba₈Al_xSi_46-xclathrate by using flux Czochralski method

Predicting Ground-State Configurations and Electronic Properties of the Thermoelectric Clathrates Ba₈Al_xSi_46–xand Sr₈Al_xSi_46–x