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Bentien, Anders; Pacheco, V.; Paschen, S.; Grin, Yu.; Steglich, F.

doi:10.1103/physrevb.71.165206

Cited by 118 publications

(97 citation statements)

References 43 publications

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“…13,14 A second challenge to the TRR model is: can the shift from crystalline to glasslike behavior be explained solely by phonon scattering mechanisms within the framework, i.e., by interactions between phonons and charge carriers? This question was raised in a series of papers by Bentien et al 15,16,18 which we now discuss.…”

Section: Discussionmentioning

confidence: 99%

“…These differences can be mostly reproduced by an increase in resonant scattering, however, an increase in both resonant and tunnelling scattering levels are required to reproduce the full set of data below 100 K. Heat capacity and single-crystal x-ray diffraction data indicated that these increases are not the result of any major change in the guest ions' vibrational behaviors, therefore a more effective coupling of the frameworks with p-type carriers to the TS and rattling vibrations of the guest ions is the most likely mechanism. The T 2 dependence in κ L (T ) obtained at lowest temperatures for both n-type and p-type Ba 8 Ga 16 Ge 30 indicates that tunnelling states should be present for the Ba(2) ions in this compound, therefore its mere presence is insufficient to guarantee glasslike κ L (T ).…”

Section: Discussionmentioning

confidence: 99%

“…One proposes that the tunnelling states are not required, only an off-center vibration of the guest ions, 13,14 and another proposes that the guest ions don't play a major role at all at low temperatures, but rather it is the phonon scattering on charge carriers that leads to the glasslike behavior. 15,16,17,18 In this work we address the issue by performing single crystal x-ray diffraction (SCXRD), thermal conductivity κ(T ) and heat capacity C p (T ) experiments on Ba 8 Ga 16 Sn 30 (BGS) and Ba 8 Ga 16 Ge 30 (BGG) crystals, which have been tuned through the crystal growth process to display n-type or p-type majority charge carriers as a result of small imbalances in their Ga:Ge or Ga:Sn ratios. 19,20 By analyzing the differences and similarities between the behaviors of these samples, we can test the applicability of the various models proposed to explain the origin of unusual glasslike behavior, in this case observed for p-type samples whereas the n-type samples show the normal crystalline peak.…”

Section: Fig 1: (Color Online)mentioning

confidence: 99%

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Glasslike versus crystalline thermal conductivity in carrier-tunedBa8Ga16X30clathrates(X<

et al. 2006

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The present controversy over the origin of glasslike thermal conductivity observed in certain crystalline materials is addressed by studies on single-crystal x-ray diffraction, thermal conductivity κ(T ) and specific heat Cp(T ) of carrier-tuned Ba8Ga16X30 (X = Ge, Sn) clathrates. These crystals show radically different low-temperature κ(T ) behaviors depending on whether their charge carriers are electrons or holes, displaying the usual crystalline peak in the former case and an anomalous glasslike plateau in the latter. In contrast, Cp(T ) above 4 K and the general structural properties are essentially insensitive to carrier tuning. We analyze these combined results within the framework of a Tunneling/Resonant/Rayleigh scatterings model, and conclude that the evolution from crystalline to glasslike κ(T ) is accompanied by an increase both in the effective density of tunnelling states and in the resonant scattering level, while neither one of these contributions can solely account for the observed changes in the full temperature range. This suggests that the most relevant factor which determines crystalline or glasslike behavior is the coupling strength between the guest vibrational modes and the frameworks with different charge carriers.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Fig 1: (Color Online)mentioning

confidence: 99%

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Glasslike versus crystalline thermal conductivity in carrier-tunedBa8Ga16X30clathrates(X<

et al. 2006

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“…Using a linear extrapolation of the thermal conductivity data to higher temperatures, it is estimated to reach a maximum of ZT max % 0.2 at 680 K. This is higher than for n-type Ba 8 Ga 6 Ge 40 (ZT max % 0.02 at 300 K) 12 but lower than for n-type a-and b-Eu 8 Ga 16 Ge 30 (ZT max % 0.4 at 400 K). 13 For thermoelectric applications, the Seebeck coefficient and the resistivity need to be improved by optimizing the Ni content and thus the carrier concentration. …”

Section: Resultsmentioning

confidence: 99%

Physical Properties of Single-Crystalline Ba8Ni3.5Ge42.1□0.4

Nguyen

Aydemir

Baitinger

et al. 2010

Journal of Elec Materi

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Clathrates are candidate materials for thermoelectric applications because of a number of unique properties. The clathrate I phases in the Ba-Ni-Ge ternary system allow controlled variation of the charge carrier concentration by adjusting the Ni content. Depending on the Ni content, the physical properties vary from metal-like to insulator-like and show a transition from p-type to n-type conduction. Here we present first results on the characterization of millimeter-sized single crystals grown by the Bridgman technique. Single crystals with a composition of Ba 8 Ni 3.5 Ge 42.1 h 0.4 show metallic behavior (dq/dT > 0) albeit with high resistivity at room temperature [q (300 K) = 1 mX cm]. The charge carrier concentration at 300 K, as determined from Hall-effect measurements, is 2.3 e À /unit cell. The dimensionless thermoelectric figure of merit estimated at 680 K is ZT % 0.2.

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“…The analysis of the XRD data shows similar size of the grains in the range of several micrometers for all samples. Since the expected mean free path of charge carriers in Ba 8 Ga 16 Ge 30 and other similar clathrates is in the range of 1-300 Å at 2 K and is reduced with temperature [30][31][32] it is concluded that grain size effects cannot explain the behavior of the resistiv-FIG. 1.…”

Section: Electrical Resistivitymentioning

confidence: 99%

Thermoelectric properties of partly Sb- and Zn-substituted Ba8Ga16Ge30 clathrates

Cederkrantz

Nygren

Palmqvist

2010

Journal of Applied Physics

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The effects on the thermoelectric properties of n-Ba8Ga16Ge30 when substituting small amounts of the Ga or Ge with Sb or Zn have been investigated. A number of syntheses were prepared in quaternary systems of Ba8Ga16Ge30 substituted with either Sb or Zn but only three samples were found to yield single phase products with nominal compositions of Ba8Ga15Sb1Ge30, Ba8Ga15Zn1Ge30 and Ba8Ga16Ge28Zn2, respectively. When Ge was substituted for Zn the resulting sample remained n-type and an increase in thermopower and a decrease in thermal conductivity were achieved. These positive effects were accompanied with an increased electrical resistivity and thus the ZT was only somewhat improved up to about 400 °C. When substituting Ga with either Sb or Zn samples remained n-type but showed decreased thermopower and increased electrical resistivity and thermal conductivity. It is thus concluded that substitution of Ga with Zn or Sb is detrimental for the thermoelectric properties of Ba8Ga16Ge30, whereas substitution of Ge with Zn appears a potent method for improving its performance.

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Transport properties of composition tunedα- andβ−Eu8Ga16−x

Cited by 118 publications

References 43 publications

Glasslike versus crystalline thermal conductivity in carrier-tunedBa8Ga16X30clathrates(X<

Glasslike versus crystalline thermal conductivity in carrier-tunedBa8Ga16X30clathrates(X<

Physical Properties of Single-Crystalline Ba8Ni3.5Ge42.1□0.4

Thermoelectric properties of partly Sb- and Zn-substituted Ba8Ga16Ge30 clathrates

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