Heat Capacity Study on Anharmonicity in Ae8Ga16Ge30 (Ae = Sr and Ba)

Xu, Jingtao; Tang, Jun; Sato, Kazumi; Tanabe, Yoichi; Heguri, Satoshi; Miyasaka, Hitoshi; Yamashita, Masahiro; Tanigaki, Katsumi

doi:10.1007/s11664-011-1607-z

Cited by 13 publications

(14 citation statements)

References 24 publications

(30 reference statements)

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“…The humps in C V /T 3 of type-I Ba 8 Ga 16 Sn 30 (β-BGS) and type-I Sr 8 Ga 16 Ge 30 appear around T ≃5 [K] (Avila et al, 2008;Suekuni et al, 2007Suekuni et al, , 2008aUmeo et al, 2005;Xu et al, 2011). See Fig.…”

Section: Excess Specific Heats Over Debye Phonons At Temperatures Of ...mentioning

confidence: 97%

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

et al. 2014

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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.

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Section: Excess Specific Heats Over Debye Phonons At Temperatures Of ...mentioning

confidence: 97%

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

et al. 2014

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“…Several others have recognized this and have attempted to provide evidence for these properties while others have modified the model to make the TLS and distribution more meaningful [11,24,50,51]. A major flaw in this theory is this lack of understanding the source and distribution of the TLSs.…”

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confidence: 99%

Lattice vacancies responsible for the linear dependence of the low-temperature heat capacity of insulating materials

Schliesser

Woodfield

2015

Phys. Rev. B

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The linear dependence on temperature (γT) of the heat capacity at low temperatures (T < 15 K) is traditionally attributed to conduction electrons in metals; however, many insulators also exhibit a linear dependence that has been attributed to a variety of other physical properties. The property most commonly used to justify the presence of this linear dependence is lattice vacancies, but a correlation between these two properties has never been shown. We have devised a theory that justifies a linear heat capacity as a result of lattice vacancies, and we provide measured values and data from the literature to support our arguments. We postulate that many small Schottky anomalies are produced by a puckering of the lattice around these vacancies, and variations in the lattice caused by position or proximity to some form of structure result in a distribution of Schottky anomalies with different energies. We present a mathematical model to describe these anomalies and their distribution based on literature data that ultimately results in a linear heat capacity. From these calculations, a quantitative relationship between the linear term and the concentration of lattice vacancies is identified, and we verify these calculations using values of γ and vacancy concentrations for several materials. We have compiled many values of γ and vacancy concentrations from the literature which show several significant trends that provide further evidence for our theory.

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“…Typically, such excess specific heats due to guest "rattling" can be associated with the peak occurring in a temperature range whose center is normally 10-100 times smaller than the Debye temperature [37]. Previous reports identified the characteristic humps that were determined around T~5 K, in the case of Type-I β-Rb 8 Ga 16 Sn 30 (β-RGS) and Type-I Sr 8 Ga 16 Ge 30 [38][39][40][41][42][43] compounds. Our computational work presents this form of hump in the Type-II Rb 24 Ga 24 Sn 112 clathrate, owing primarily to two sorts of isotropic Einstein oscillators that originate from the 28 atom and 20 atom cages, respectively.…”

Section: Vibrtional and Thermal Properties Of Rb 24 Ga 24 Sn 112 And mentioning

confidence: 99%

First Principles Study of the Vibrational and Thermal Properties of Sn-Based Type II Clathrates, CsxSn136 (0 ≤ x ≤ 24) and Rb24Ga24Sn112

2019

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After performing first-principles calculations of structural and vibrational properties of the semiconducting clathrates Rb24Ga24Sn112 along with binary CsxSn136 (0 ≤ x ≤ 24), we obtained equilibrium geometries and harmonic phonon modes. For the filled clathrate Rb24Ga24Sn112, the phonon dispersion relation predicts an upshift of the low-lying rattling modes (~25 cm−1) for the Rb (“rattler”) compared to Cs vibration in CsxSn136. It is also found that the large isotropic atomic displacement parameter (Uiso) exists when Rb occupies the “over-sized” cage (28 atom cage) rather than the 20 atom counterpart. These guest modes are expected to contribute significantly to minimizing the lattice’s thermal conductivity (κL). Our calculation of the vibrational contribution to the specific heat and our evaluation on κL are quantitatively presented and discussed. Specifically, the heat capacity diagram regarding CV/T3 vs. T exhibits the Einstein-peak-like hump that is mainly attributable to the guest oscillator in a 28 atom cage, with a characteristic temperature 36.82 K for Rb24Ga24Sn112. Our calculated rattling modes are around 25 cm−1 for the Rb trapped in a 28 atom cage, and 65.4 cm−1 for the Rb encapsulated in a 20 atom cage. These results are utilized to predict the lattice’s thermal conductivity (approximately 0.62 W/m/K) in Rb24Ga24Sn112 within the kinetic theory approximation.

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Heat Capacity Study on Anharmonicity in Ae8Ga16Ge30 (Ae = Sr and Ba)

Cited by 13 publications

References 24 publications

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

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

Lattice vacancies responsible for the linear dependence of the low-temperature heat capacity of insulating materials

First Principles Study of the Vibrational and Thermal Properties of Sn-Based Type II Clathrates, CsxSn136 (0 ≤ x ≤ 24) and Rb24Ga24Sn112

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