Interacting dipoles in type-I clathrates: Why glass-like though crystalline?

Nakayama, Tsuneyoshi; Kaneshita, Eiji

doi:10.1209/0295-5075/84/66001

Cited by 19 publications

(24 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Equation (66) predicts larger specific heats for smaller dipole moments p, but η vanishes with p → 0 (Nakayama and Kaneshita, 2008). A carrier-type dependence on C tun (T ) has been observed by Suekuni et al (2008a) for n-and p-type β-BGS with deviations U 0 = 0.434 and 0.439 [Å], respectively.…”

Section: Explicit Form Of Specific Heats Below 1 Kmentioning

confidence: 67%

“…This naive view misleads in that it suggests an isolated non-interacting picture could explain the observed glass-like behaviors. Such a non-interacting picture does not reproduce the observed temperature dependence as well as the magnitudes of the specific heats for type-I clathrate compounds with off-center guest atoms at 1 [K] and below (Nakayama and Kaneshita, 2008). In fact, as will be discussed in the next section, the tunneling between the nearby potential minima in configuration space generated by a combination of interacting dipoles is crucial for interpreting glass-like thermal properties at low temperatures.…”

Section: Specific Heats Below 1 [K]mentioning

confidence: 99%

See 1 more Smart Citation

Phonon-glass electron-crystal thermoelectric clathrates: Experiments and theory

et al. 2014

View full text Add to dashboard Cite

Type-I clathrate compounds have attracted a great deal of interest in connection with the search for efficient thermoelectric materials. These compounds constitute networked cages consisting of nano-scale tetrakaidecahedrons (14 hedrons) and dodecahedrons (12 hedrons), in which the group 1 or 2 elements in the periodic table are encaged as the so-called "rattling" guest atom. It is remarkable that, though these compounds have crystalline cubic-structure, they exhibit glasslike phonon thermal conductivity over the whole temperature range depending on the states of rattling guest atoms in the tetrakaidecahedron. In addition, these compounds show unusual glass-like specific heats and THz-frequency phonon dynamics, providing a remarkable broad peak almost identical to those observed in topologically disordered amorphous materials or structural glasses, the so-called Boson peak. An efficient thermoelectric effect is realized in compounds showing these glass-like characteristics. This decade, a number of experimental works dealing with type-I clathrate compounds have been published. These are diffraction experiments, thermal and spectroscopic experiments in addition to those based on heat and electronic transport. These form the raw materials for this article based on advances this decade. The subject of this article involves interesting phenomena from the viewpoint of not only physics but also from the view point of the practical problem of elaborating efficient thermoelectric materials. This review presents a survey of a wide range of experimental investigations of type-I clathrate compounds, together with a review of theoretical interpretations of the peculiar thermal and dynamic properties observed in these materials.

show abstract

Section: Explicit Form Of Specific Heats Below 1 Kmentioning

confidence: 67%

Section: Specific Heats Below 1 [K]mentioning

confidence: 99%

Phonon-glass electron-crystal thermoelectric clathrates: Experiments and theory

et al. 2014

View full text Add to dashboard Cite

show abstract

“…The random orientation of the vector U ℓ originates from four hollows of the anharmonic potential 4,24) in addition to inter-site dipole-dipole interactions between off-center guest ions. 25,26) It has been confirmed 4) that off-centered guest ions experience a hindering potential V h (θ) with a fourfold inversion symmetry along the azimuthal direction.…”

Section: Potential For Off-centered Guest Ionsmentioning

confidence: 92%

“…The first-principles calculations have shown V h to be ≃ 20 K for Sr 2+ guest ions in β-SGG. 24) The effect of long-range electrostatic force has been treated in our papers 25,26) for the elucidation of glass-like behaviours of OFS at low temperatures. Electric dipole moments of guest ions provide long-range interactions with dipoles in other cages.…”

Section: Potential For Off-centered Guest Ionsmentioning

confidence: 99%

Significance of Off-Center Rattling for Emerging Low-Lying THz Modes in Type-I Clathrates

Nakayama

Kaneshita

2011

J. Phys. Soc. Jpn.

View full text Add to dashboard Cite

We show that the distinct differences of low-lying THz-frequency dynamics between type-I clathrates with on-center and off-center guest ions naturally follow from a theoretical model taking into account essential features of the dynamics of rattling guest ions. Our model analysis demonstrates the drastic change from the conventional dynamics shown by on-center systems to the peculiar dynamics of off-center systems in a unified manner. We claim that glass-like plateau thermal conductivities observed for off-center systems stem from the flattening of acoustic phonon dispersion in the regime |k | < |G|/4. The mechanism is applicable to other systems such as glasses or relaxers.

show abstract

“…of thermoelectrics is their ability to conduct electricity like a crystalline solid and at the same time to conduct heat like a glass, i.e. the "phonon glass-electron crystal" paradigm [18,19]. These systems have a perfectly ordered crystalline (host) lattice but they contain caged (typically heavier) atoms referred to as "rattlers" (see Fig.1), which give rise to independent quasi-localized vibrational modes that scatter acoustic phonons and have an important impact on the energy conversion efficiency of the systems [20][21][22][23].…”

mentioning

confidence: 99%

Theory of the phonon spectrum in host-guest crystalline solids with avoided crossing

2019

View full text Add to dashboard Cite

We develop an analytical model to describe the phonon dispersion relations of thermoelectrics with heavy guest atoms (rattlers). Crucially, the model also accounts for phonon damping arising from anharmonicity. The spectrum of low energy states contains acoustic-like and (soft) optical-like modes, which display the typical avoided crossing, and which can be derived analytically by considering the dynamical coupling between host lattice and guest rattlers. Inclusion of anharmonic damping in the model allows us, for the first time, to compute the vibrational density of states (VDOS) and the specific heat, unveiling the presence of a boson peak (BP) anomaly indicating the glassy behaviour of phonons in the otherwise crystalline material. We discuss the dynamics of the BP as a function of the strength of the interaction between the soft modes and the anharmonic lattice, and of the energy gap between the two avoided-crossing branches. Upon increasing the coupling strength between the host and the guest dynamics, and by decreasing the energy of the soft optical modes, the BP anomaly becomes stronger and it moves towards lower frequencies. Moreover, we find a robust linear correlation between the BP frequency and the energy of the soft optical-like modes. Our results provide decisive evidence for the link between soft gapped modes and glassy phonon anomalies. Finally, it provides a useful model for tuning the phonon glass behaviour of thermoelectrics, which is crucial for optimizing the energy conversion efficiency in these materials.

show abstract

Interacting dipoles in type-I clathrates: Why glass-like though crystalline?

Cited by 19 publications

References 24 publications

Phonon-glass electron-crystal thermoelectric clathrates: Experiments and theory

Phonon-glass electron-crystal thermoelectric clathrates: Experiments and theory

Significance of Off-Center Rattling for Emerging Low-Lying THz Modes in Type-I Clathrates

Theory of the phonon spectrum in host-guest crystalline solids with avoided crossing

Contact Info

Product

Resources

About