Raman Scattering of Type-I Clathrate Compounds

Takasu, Yuichi; Hasegawa, Tetsuya; Ogita, Norio; Udagawa, Masayuki; Ávila, M. A.; Suekuni, Koichiro; Takabatake, Toshiro

doi:10.1143/jpsjs.77sa.254

Cited by 2 publications

(2 citation statements)

References 21 publications

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“…There is little difference between n-and p-type crystals, in accordance with several techniques used so far to study the structure of Ba 8 Ga 16 X 30 ͑X =Ge,Sn͒. 13,21,26,27 With decreasing temperature from 300 to 120 K, the isotropic displacement parameters U eq for all atoms in ␤ n1 and that for Ba͑2͒ in ␤ p1 linearly decrease, as shown in Fig. 3͑a͒.…”

Section: Crystal Growth and Structural Analysissupporting

confidence: 80%

Simultaneous structure and carrier tuning of dimorphic clathrateBa8Ga16Sn30

et al. 2008

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We report structural, transport, and thermal properties of carrier-tuned Ba 8 Ga 16 Sn 30 single crystals with the type-1 clathrate structure ͑␤ phase͒, demonstrating that Ba 8 Ga 16 Sn 30 is a unique thermoelectric clathrate material wherein both the structure type and the carrier type are tunable. The results are compared with the properties of the better known type-8 structure ͑␣ phase͒ and of A 8 Ga 16 Ge 30 ͑A =Sr,Eu͒. Differential thermal analysis and powder x-ray diffraction show that both phases are stable up to their virtually identical melting point of 520Ϯ 3°C. Refinements of single-crystal x-ray diffraction data indicate that the Ba͑2͒ guest ion in the tetrakaidecahedron occupies the off-center 24k sites which are 0.43-0.44 Å away from the centered 6d site. The temperature-linear coefficient of the specific heat is 29 mJ/ mol K 2 for both n-and p-type carriers in the ␤ phase, four times larger than that for the ␣ phase, suggesting contributions from tunneling of the Ba͑2͒ guest ions between off-center minima. Analysis of specific heat with a soft-potential model ͑SPM͒ gives a characteristic energy of 20 K for the Ba͑2͒ vibration, significantly lower than 50 K for the ␣ phase and in fact the lowest among type-1 clathrates. The lattice thermal conductivities L for the ␤ phase with both charge carrier types are very similar and show a glasslike temperature dependence. This behavior in L ͑T͒ is also described using SPM analysis, where it is found that the coupling strength between guest modes and acoustic phonons for the ␤ phase is significantly larger than that for Sr 8 Ga 16 Ge 30 .

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Section: Crystal Growth and Structural Analysissupporting

confidence: 80%

Simultaneous structure and carrier tuning of dimorphic clathrateBa8Ga16Sn30

et al. 2008

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“…Moreover, experimental evidence suggests that the degree of off-centering, the frequencies of the lowest Raman active modes and the lattice thermal conductivity are correlated for compounds in the structurally similar quaternary system Sr 8 Ga 16 Si x Ge 30−x . 55,56 Given these results, it is reasonable to assume that the lattice thermal conductivity also varies to some degree with chemical composition. We therefore computed the variation of the 18 lowest-frequency phonon modes, associated with the Ba atom at the 6d site 70 , with the number of group-13 atoms not only in Ba 8 Ga x Ge 46−x but also Ba 8 Al x Si 46−x , where the latter was included as it represents the limit of a host matrix made up of light elements.…”

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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Raman Scattering of Type-I Clathrate Compounds

Cited by 2 publications

References 21 publications

Simultaneous structure and carrier tuning of dimorphic clathrateBa8Ga16Sn30

Simultaneous structure and carrier tuning of dimorphic clathrateBa8Ga16Sn30

Thermal conductivity in intermetallic clathrates: A first-principles perspective

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