Inorganic clathrate-II materials of group 14: synthetic routes and physical properties

Beekman, Matt; Nolas, George S.

doi:10.1039/b706808e

Cited by 180 publications

(167 citation statements)

References 120 publications

(203 reference statements)

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“…It is well known that one way to reduce lattice thermal conductivity (LTC) is to introduce low-frequency lattice vibrations to scatter heat-carrying acoustic phonons (21-24). This has been proven a very effective approach for realizing the extremely low LTC through the randomly fluctuating rattling fillers on the void-sublattice interlocking with the rigid framework in filled skutterudites (23,24) and clathrates (14,25,26). In both systems, all void fillers are individually embedded in a flattened potential energy surface due to the weak bonding or interaction with the framework (12,13,22,23,27,28) and show ultralarge atom displacement parameters (ADPs).…”

Section: Resultsmentioning

confidence: 99%

Part-crystalline part-liquid state and rattling-like thermal damping in materials with chemical-bond hierarchy

Qiu

Wei

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

238

209

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Understanding thermal and phonon transport in solids has been of great importance in many disciplines such as thermoelectric materials, which usually requires an extremely low lattice thermal conductivity (LTC). By analyzing the finite-temperature structural and vibrational characteristics of typical thermoelectric compounds such as filled skutterudites and Cu 3 SbSe 3 , we demonstrate a concept of part-crystalline part-liquid state in the compounds with chemicalbond hierarchy, in which certain constituent species weakly bond to other part of the crystal. Such a material could intrinsically manifest the coexistence of rigid crystalline sublattices and other fluctuating noncrystalline sublattices with thermally induced largeamplitude vibrations and even flow of the group of species atoms, leading to atomic-level heterogeneity, mixed part-crystalline partliquid structure, and thus rattling-like thermal damping due to the collective soft-mode vibrations similar to the Boson peak in amorphous materials. The observed abnormal LTC close to the amorphous limit in these materials can only be described by an effective approach that approximately treats the rattling-like damping as a "resonant" phonon scattering.sublattice melting | partial Grüneisen parameter | first principles | anharmonicity U nderstanding thermal and phonon transport in solids has been of great importance in many disciplines such as thermoelectrics (1-3), phononic materials (4), and thermal management composites (5). The interplay among chemical bonds, lattice dynamics, and thermal transport in materials is also an attractive topic in condensed matter physics (6) and materials science (7). Thermal transport is a key issue in thermoelectric (TE) energy-conversion materials, which are regarded among the potential candidates for revolutionizing waste-heat recovery (2, 7-9). The dimensionless figure of merit of a TE material is defined as ZT = TS 2 σ=κ, where T, S, σ, and κ are the absolute temperature, Seebeck coefficient, electrical conductivity, and thermal conductivity, respectively. To improve the efficiency of TE conversion, many approaches aim at reducing the thermal conductivity, especially the lattice part, to a minimum level, namely the realization of phonon-glass-like thermal transport (1, 7).TE materials research primarily focuses on solid and crystalline thermoelectrics. It has been long viewed that all solids contain strong interatomic interactions without even an exception, and thus the established approaches to describe thermal transports in crystalline solids, including TE solids, are solely based on the perturbative "small-parameter" approximation to lattice dynamics of atoms around their equilibrium positions, i.e., phonons and phonon-phonon interactions (10, 11). As a result, crystallographic homogeneity at the atomic level in solid materials has overwhelmingly been accepted. However, recent work on exploring novel TE materials went noticeably beyond the conventional knowledge of solid TE compounds being ideally crystalline, atomically...

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Section: Resultsmentioning

confidence: 99%

Part-crystalline part-liquid state and rattling-like thermal damping in materials with chemical-bond hierarchy

Qiu

Wei

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

238

209

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“…Although a rich phase space can be inferred, very few compositions are experimentally known [5]. Previously reported crystallographic [6], Raman 6 Author to whom any correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 99%

A study of low-energy guest phonon modes in clathrate-II Na_xSi₁₃₆(x= 3, 23, and 24)

Beekman

Hermann

Möchel

et al. 2010

J. Phys.: Condens. Matter

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Single-crystal x-ray diffraction from clathrate-II Na x Si 136 (x = 24) prepared by a new technique reveals the exceptionally large Na@Si 28 atomic displacement parameter (U eq ) is strongly temperature dependent, and can be attributed to low-energy rattling modes associated with the Na guest. Inelastic neutron scattering (INS) spectra collected from Na x Si 136 powder specimens (x = 3, 23) confirm the presence of low-energy guest-derived phonon modes for Na@Si 28 and Na@Si 20 . The lower energy Na@Si 28 rattler mode falls in the frequency range of the silicon host acoustic phonons, indicating the possibility for interaction with these phonons. The presence of these low-energy modes combined with the ability to controllably vary the guest content presents a unique opportunity for exploring the influence of guest-framework interactions on the lattice dynamics in intermetallic clathrates.

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“…The close relationship between structure and properties is of scientific and technological importance 7,8 . Among other applications,…”

Section: Introductionmentioning

confidence: 99%

Vibrational dynamics of the host framework in Sn clathrates

Leu

Sturza

et al. 2014

Phys. Rev. B

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We use nuclear resonance inelastic X-ray scattering (NRIXS), a relatively new, synchrotronbased, isotope-specific technique in combination with a more traditional one, Raman spectroscopy, to probe the vibrational dynamics of the host frameworks in two Zintl clathrates: K 8 Zn 4 Sn 42 (KZS) and Ba 8 Ga 16 Sn 30 (BGS). From the normalized Sn vibrational density of states obtained from NRIXS we calculate the stiffness, a mean force constant of the Sn environment, the resilience, a compact way of expressing the temperature dependence of the Sn mean square displacement, and several thermodynamic properties. The stiffness and the resilience are approximately 7% lower in KZS, reflecting its larger unit cell compared to BGS. We emphasize the complementariness between NRIXS and Raman spectroscopy and establish a series of benchmarks for a more quantitative evaluation of the Raman spectra for the numerous clathrates that are still not suitable for NRIXS studies.

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Inorganic clathrate-II materials of group 14: synthetic routes and physical properties

Cited by 180 publications

References 120 publications

Part-crystalline part-liquid state and rattling-like thermal damping in materials with chemical-bond hierarchy

Part-crystalline part-liquid state and rattling-like thermal damping in materials with chemical-bond hierarchy

A study of low-energy guest phonon modes in clathrate-II Na_xSi₁₃₆(x= 3, 23, and 24)

Vibrational dynamics of the host framework in Sn clathrates

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Inorganic clathrate-II materials of group 14: synthetic routes and physical properties

Cited by 180 publications

References 120 publications

Part-crystalline part-liquid state and rattling-like thermal damping in materials with chemical-bond hierarchy

Part-crystalline part-liquid state and rattling-like thermal damping in materials with chemical-bond hierarchy

A study of low-energy guest phonon modes in clathrate-II NaxSi136(x= 3, 23, and 24)

Vibrational dynamics of the host framework in Sn clathrates

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A study of low-energy guest phonon modes in clathrate-II Na_xSi₁₃₆(x= 3, 23, and 24)