Splitting of Guest Atom Sites and Lattice Thermal Conductivity in Ba-Ga-Ge Clathrate Compounds

2005 ◽  
Vol 886 ◽  
Author(s):  
Norihiko L. Okamoto ◽  
Katsushi Tanaka ◽  
Haruyuki Inui
Keyword(s):  
Thermal Conductivity ◽  
Room Temperature ◽  
Lattice Thermal Conductivity ◽  
Inverse Correlation ◽  
Atomic Displacement ◽  
Dominant Factor ◽  
Type I ◽  
Cage Structure ◽  
Clathrate Compounds ◽  
Guest Atom

ABSTRACTThe crystal structures of some type-I and -III clathrate compounds in the Ba-Ga-Ge system have been investigated by synchrotron X-ray powder diffraction at room temperature, paying special attention to the changes of the cage structure and the splitting behavior at the guest atom site upon alloying with Ga. For both types of the clathrate compounds, the split distance of the Ba(2) sites increases with the increase in the Ga content, corresponding to the change in the size and shape of the encapsulating polyhedral cage. Lattice thermal conductivity at room temperature has a positive correlation with the atomic displacement parameter (ADPsplit) based on the split-site model but has an inverse correlation with the split distance of the Ba(2) sites, indicating that a dominant factor of reducing the lattice thermal conductivity is not thermal vibration at the split sites but thermal jump among the split sites.

Variation in the Einstein Temperature of Guest Atoms in Ba-Ge-X type-III Clathrate Compounds

2007 ◽  
Vol 1044 ◽  
Author(s):  
Katsushi Tanaka ◽  
Jung-Hwan Kim ◽  
Kyosuke Kishida ◽  
Haruyuki Inui
Keyword(s):  
Thermal Conductivity ◽  
Temperature Dependence ◽  
Lattice Thermal Conductivity ◽  
Atomic Displacement ◽  
X Ray ◽  
Type Iii ◽  
Clathrate Compounds ◽  
Einstein Temperature ◽  
Small Lattice ◽  
Atomic Displacement Parameters

AbstractEinstein temperatures of guest atoms in Ba-Ge-(Al, In) type-III clathrate compounds have been estimated from the temperature dependence of the atomic displacement parameters determined by synchrotron X-ray powder diffractions. The lowest temperature is obtained for the vibration of Ba(2) atoms along the x-direction, which corresponds to the “rattling motion” of the guest atoms in the compounds. The temperature estimated is significantly low of about 50 K, which agrees with the fact that the compounds have small lattice thermal conductivities of about 0.6 W/mK. Though the lattice thermal conductivity of Ba24Ge88Al12 is larger than that of Ba24Ge88In12, the Einstein temperature of Ba24Ge88Al12 is slightly smaller than that of Ba24Ge88In12. This discrepancy can be explained by the consideration of higher Debye temperature of Ba24Ge88Al12 than that of Ba24Ge88In12, that is, lattice thermal conductivity without “rattling motion” is larger for Ba24Ge88Al12 than that for Ba24Ge88In12.

Connections between Crystallographic Data and New Thermoelectric Compounds

2000 ◽  
Vol 626 ◽  
Author(s):  
B. C. Sales ◽  
B. C. Chakoumakos ◽  
D. Mandrus
Keyword(s):  
Crystal Structure ◽  
Thermal Conductivity ◽  
Thermoelectric Materials ◽  
Room Temperature ◽  
Lattice Thermal Conductivity ◽  
Atomic Displacement ◽  
High Symmetry ◽  
Structure Property ◽  
Weakly Bound ◽  
Atomic Displacement Parameters

ABSTRACTNew bulk thermoelectric compounds are normally discovered with the aid of simple qualitative structure-property relationships. Most good thermoelectric materials are narrow gap semiconductors composed of heavy elements with similar electronegativities. The crystal structures are usually of high symmetry (cubic, hexagonal, and possibly tetragonal), and often contain a large number of atoms per unit cell. In the present work a new structure-property relationship is discussed which links atomic displacement parameters (ADPs) and the lattice thermal conductivity of clathrate-like compounds. For many clathrate-like compounds, in which one of the atom-types is weakly bound and “rattles” within its atomic cage, room temperature ADP information can be used to estimate the room temperature lattice thermal conductivity, the vibration frequency of the “rattler”, and the temperature dependence of the heat capacity. ADPs are reported as part of the crystal structure description, and hence APDs represent some of the first information that is known about a new compound. For most ternary and quaternary compounds, all that is known is its crystal structure. ADP information thus provides a useful screening tool for the large and growing crystallographic databases. Examples of the use and limitations of this analysis are presented for several promising classes of thermoelectric materials.

scholarly journals Local ferroelectric polarization switching driven by nanoscale distortions in thermoelectric $${\text {Sn}}_{0.7}{\text {Ge}}_{0.3}{\text {Te}}$$

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Aastha Vasdev ◽  
Moinak Dutta ◽  
Shivam Mishra ◽  
Veerpal Kaur ◽  
Harleen Kaur ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Figure Of Merit ◽  
Room Temperature ◽  
Lattice Thermal Conductivity ◽  
Direct Evidence ◽  
Temperature Dependent ◽  
Force Microscopy ◽  
Ferroelectric Domains ◽  
Pdf Analysis ◽  
Ferroelectric Transition Temperature

AbstractA remarkable decrease in the lattice thermal conductivity and enhancement of thermoelectric figure of merit were recently observed in rock-salt cubic SnTe, when doped with germanium (Ge). Primarily, based on theoretical analysis, the decrease in lattice thermal conductivity was attributed to local ferroelectric fluctuations induced softening of the optical phonons which may strongly scatter the heat carrying acoustic phonons. Although the previous structural analysis indicated that the local ferroelectric transition temperature would be near room temperature in $${\text {Sn}}_{0.7}{\text {Ge}}_{0.3}{\text {Te}}$$ Sn 0.7 Ge 0.3 Te , a direct evidence of local ferroelectricity remained elusive. Here we report a direct evidence of local nanoscale ferroelectric domains and their switching in $${\text {Sn}}_{0.7}{\text {Ge}}_{0.3}{\text {Te}}$$ Sn 0.7 Ge 0.3 Te using piezoeresponse force microscopy(PFM) and switching spectroscopy over a range of temperatures near the room temperature. From temperature dependent (250–300 K) synchrotron X-ray pair distribution function (PDF) analysis, we show the presence of local off-centering distortion of Ge along the rhombohedral direction in global cubic $${\text {Sn}}_{0.7}{\text {Ge}}_{0.3}{\text {Te}}$$ Sn 0.7 Ge 0.3 Te . The length scale of the $${\text {Ge}}^{2+}$$ Ge 2 + off-centering is 0.25–0.10 Å near the room temperatures (250–300 K). This local emphatic behaviour of cation is the cause for the observed local ferroelectric instability, thereby low lattice thermal conductivity in $${\text {Sn}}_{0.7}{\text {Ge}}_{0.3}{\text {Te}}$$ Sn 0.7 Ge 0.3 Te .

Thermoelectric Properties of CoSb3-based Skutterudite Compounds

2010 ◽  
Vol 1267 ◽  
Author(s):  
Adul Harnwunggmoung ◽  
Ken Kurosaki ◽  
Hiroaki Muta ◽  
Shinsuke Yamanaka
Keyword(s):  
Thermal Conductivity ◽  
Thermoelectric Properties ◽  
Figure Of Merit ◽  
Room Temperature ◽  
Lattice Thermal Conductivity ◽  
Filling Ratio ◽  
Thermoelectric Figure Of Merit ◽  
Thermoelectric Figure ◽  
Alloy Scattering ◽  
Skutterudite Compound

AbstractCoSb3 is known as a skutterudite compound that could exhibit high thermoelectric figure of merit. However, the thermal conductivity of CoSb3 is relatively high. In order to enhance the thermoelectric performance of this compound, we tried to reduce the thermal conductivity of CoSb3 by substitution of Rh for Co and by Tl-filling into the voids. The polycrystalline samples of (Co,Rh)Sb3 and Tl-filled CoSb3 were prepared and the thermoelectric properties such as the Seebeck coefficient, electrical resistivity, and thermal conductivity were measured in the temperature range from room temperature to 750 K. The Rh substitution for Co reduced the lattice thermal conductivity, due to the alloy scattering effect. The minimum value of the lattice thermal conductivity was 4 Wm-1K-1 at 750 K obtained for (Co0.7Rh0.3)Sb3. Also the lattice thermal conductivity rapidly decreased with increasing the Tl-filling ratio. T10.25Co4Sb12 exhibited the best ZT values; the maximum ZT was 0.9 obtained at 600 K.

Design Concepts for Improved Thermoelectric Materials

1997 ◽  
Vol 478 ◽  
Author(s):  
Glen A. Slack
Keyword(s):  
Thermal Conductivity ◽  
Thermoelectric Materials ◽  
Lattice Thermal Conductivity ◽  
Design Concepts ◽  
Clathrate Compounds ◽  
New Guidelines ◽  
Better Than

AbstractSome new guidelines are given that should be useful in the search for thermoelectric materials that are better than those currently available. In particular, clathrate and crypto-clathrate compounds with filler atoms in their cages offer the ability to substantially lower the lattice thermal conductivity.

scholarly journals Effect of rattling motion without cage structure on lattice thermal conductivity in LaOBiS2−xSex

2018 ◽  
Vol 112 (2) ◽  
pp. 023903 ◽  
Author(s):  
C. H. Lee ◽  
A. Nishida ◽  
T. Hasegawa ◽  
H. Nishiate ◽  
H. Kunioka ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Lattice Thermal Conductivity ◽  
Cage Structure

scholarly journals Dimer rattling mode induced low thermal conductivity in an excellent acoustic conductor

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Ji Qi ◽  
Baojuan Dong ◽  
Zhe Zhang ◽  
Zhao Zhang ◽  
Yanna Chen ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Single Crystals ◽  
Layered Structure ◽  
First Principles ◽  
Sound Speed ◽  
Lattice Dynamics ◽  
Room Temperature ◽  
Lattice Thermal Conductivity ◽  
Atomic Structures ◽  
Order Of Magnitude

Abstract A solid with larger sound speeds usually exhibits higher lattice thermal conductivity. Here, we report an exception that CuP2 has a quite large mean sound speed of 4155 m s−1, comparable to GaAs, but single crystals show very low lattice thermal conductivity of about 4 W m−1 K−1 at room temperature, one order of magnitude smaller than GaAs. To understand such a puzzling thermal transport behavior, we have thoroughly investigated the atomic structures and lattice dynamics by combining neutron scattering techniques with first-principles simulations. This compound crystallizes in a layered structure where Cu atoms forming dimers are sandwiched in between P atomic networks. In this work, we reveal that Cu atomic dimers vibrate as a rattling mode with frequency around 11 meV, which is manifested to be remarkably anharmonic and strongly scatters acoustic phonons to achieve the low lattice thermal conductivity.

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