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.

Atomic Displacement Parameters: A Useful Tool in the Search for New Thermoelectric Materials?

1998 ◽  
Vol 545 ◽  
Author(s):  
B. C. Sales ◽  
B. C. Chakoumakos ◽  
D. Mandrus ◽  
J. W. Sharp ◽  
N. R. Dilley ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermoelectric Materials ◽  
Lattice Thermal Conductivity ◽  
Mean Square Displacement ◽  
Atomic Displacement ◽  
Weakly Bound ◽  
The Mean ◽  
Atomic Displacement Parameters ◽  
Localized Vibrational Modes ◽  
Theoretical Minimum

AbstractThe atomic displacement parameters (ADPs) measure the mean-square displacement amplitude of an atom about its equilibrium position in a crystal. It is demonstrated that the ADPs can be used to identify crystalline solids with unusually low lattice thermal conductivties. A low lattice thermal conductivity is essential in the design of thermoelectric materials with improved efficiencies.The atomic displacement parameters (ADPs) have been measured using powder neutron diffraction as a function of temperature for several clathrate-like compounds (RxCo4-yFeySb12, where R= La, Ce, Yb or TI, x=0.22, 0.8, 1, y=0, 1;Tl2SnTe5 and Tl2GeTe5). The ADP data show that in each of the compounds one of the atoms is weakly bound and “rattles” within its atomic cage. This atomic “rattling” severely reduces the ability of these crystals to conduct heat and in some cases the lattice thermal conductivity approaches the theoretical minimum value. In many clathrate-like compounds, the ADP can also be used to estimate the Einstein frequency of the “rattler”, and to predict the existence of localized vibrational modes.

scholarly journals The origin of the lattice thermal conductivity enhancement at the ferroelectric phase transition in GeTe

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Đorđe Dangić ◽  
Olle Hellman ◽  
Stephen Fahy ◽  
Ivana Savić
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Phase Transitions ◽  
Thermoelectric Materials ◽  
Ferroelectric Phase Transition ◽  
Lattice Thermal Conductivity ◽  
Ferroelectric Phase ◽  
Structural Phase ◽  
High Symmetry ◽  
Structural Phase Transitions

AbstractThe proximity to structural phase transitions in IV-VI thermoelectric materials is one of the main reasons for their large phonon anharmonicity and intrinsically low lattice thermal conductivity κ. However, the κ of GeTe increases at the ferroelectric phase transition near 700 K. Using first-principles calculations with the temperature dependent effective potential method, we show that this rise in κ is the consequence of negative thermal expansion in the rhombohedral phase and increase in the phonon lifetimes in the high-symmetry phase. Strong anharmonicity near the phase transition induces non-Lorentzian shapes of the phonon power spectra. To account for these effects, we implement a method of calculating κ based on the Green-Kubo approach and find that the Boltzmann transport equation underestimates κ near the phase transition. Our findings elucidate the influence of structural phase transitions on κ and provide guidance for design of better thermoelectric materials.

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.

Thermoelectric Properties of Two Ternary Tellurides

1998 ◽  
Vol 545 ◽  
Author(s):  
Jeff W. Sharp ◽  
Brian C. Sales ◽  
David G. Mandrus ◽  
Bryan C. Chakoumakos
Keyword(s):  
Thermal Conductivity ◽  
Thermoelectric Properties ◽  
Figure Of Merit ◽  
Lattice Thermal Conductivity ◽  
Atomic Displacement ◽  
Thermal Expansion Coefficients ◽  
Good Figure ◽  
Atomic Displacement Parameters ◽  
Binary Compounds ◽  
P Type

AbstractWe present initial assessments of the thermoelectric properties of two ternary tellurides with known crystal structures, Tl2GeTeM5 and Tl2SnTe5. Tl2SnTe5 appears to have a p-type figure of merit about the same as that of Bi2Te3, the best thermoelectric material among binary compounds. A good figure of merit is possible because the lattice thermal conductivity is very low. Based on neutron diffraction data, we have calculated atomic displacement parameters and thermal expansion coefficients. The atomic displacement parameters give some understanding of the low lattice thermal conductivity.

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.

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 .

scholarly journals Crystal Structure of Moganite and Its Anisotropic Atomic Displacement Parameters Determined by Synchrotron X-ray Diffraction and X-ray/Neutron Pair Distribution Function Analyses

Minerals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 272
Author(s):  
Seungyeol Lee ◽  
Huifang Xu ◽  
Hongwu Xu ◽  
Joerg Neuefeind
Keyword(s):  
Crystal Structure ◽  
Distribution Function ◽  
Single Crystal ◽  
Pair Distribution Function ◽  
Atomic Displacement ◽  
Single Crystal Xrd ◽  
X Ray Diffraction ◽  
X Ray ◽  
Neutron Pair ◽  
Atomic Displacement Parameters

The crystal structure of moganite from the Mogán formation on Gran Canaria has been re-investigated using high-resolution synchrotron X-ray diffraction (XRD) and X-ray/neutron pair distribution function (PDF) analyses. Our study for the first time reports the anisotropic atomic displacement parameters (ADPs) of a natural moganite. Rietveld analysis of synchrotron XRD data determined the crystal structure of moganite with the space group I2/a. The refined unit-cell parameters are a = 8.7363(8), b = 4.8688(5), c = 10.7203(9) Å, and β = 90.212(4)°. The ADPs of Si and O in moganite were obtained from X-ray and neutron PDF analyses. The shapes and orientations of the anisotropic ellipsoids determined from X-ray and neutron measurements are similar. The anisotropic ellipsoids for O extend along planes perpendicular to the Si-Si axis of corner-sharing SiO4 tetrahedra, suggesting precession-like movement. Neutron PDF result confirms the occurrence of OH over some of the tetrahedral sites. We postulate that moganite nanomineral is stable with respect to quartz in hypersaline water. The ADPs of moganite show a similar trend as those of quartz determined by single-crystal XRD. In short, the combined methods can provide high-quality structural parameters of moganite nanomineral, including its ADPs and extra OH position at the surface. This approach can be used as an alternative means for solving the structures of crystals that are not large enough for single-crystal XRD measurements, such as fine-grained and nanocrystalline minerals formed in various geological environments.

Investigation of Thermoelectric Materials: Substitution effect of Bi on the Ag1-xPb18MTe20 (M = Sb, Bi) (x = 0, 0.14, 0.3)

2007 ◽  
Vol 1044 ◽  
Author(s):  
Mi-kyung Han ◽  
Huijun Kong ◽  
Ctirad Uher ◽  
Mercouri G Kanatzidis
Keyword(s):  
Thermal Conductivity ◽  
Electrical Conductivity ◽  
Seebeck Coefficient ◽  
Thermoelectric Materials ◽  
Figure Of Merit ◽  
Lattice Thermal Conductivity ◽  
Substitution Effect ◽  
Dimensionless Figure Of Merit ◽  
The Matrix ◽  
Mass Fluctuation

AbstractWe performed comparative investigations of the Ag1-xPb18MTe20 (M = Bi, Sb) (x = 0, 0.14, 0.3) system to better understand the roles of Sb and Bi on the thermoelectric properties. In both systems, the electrical conductivity nearly keeps the same values, while the Seebeck coefficient decreases dramatically in going from Sb to Bi. Compared to the lattice thermal conductivity of PbTe, that of AgPb18BiTe20 is substantially reduced. The lattice thermal conductivity of the Bi analog, however, is higher than that of AgPb18SbTe20 and this is attributed largely to the decrease in the degree of mass fluctuation between the nanostructures and the matrix (for the Bi analog). As a result the dimensionless figure of merit ZT of Ag1-xPb18MTe20 (M = Bi) is found to be smaller than that of Ag1-xPb18MTe20 (M = Sb).

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