Room Temperature Lattice Thermal Conductivity Research Articles

Synergistic Strategy to Enhance the Thermoelectric Properties of CoSbS1-xSex Compounds via Solid Solution.

High thermal conductivity of CoSbS-based limited its own prospect application in thermoelectric energy conversion. Solid solution is an effective approach to optimize the performance of thermoelectric materials with high lattice thermal conductivity because of the enhanced phonons scattering from disorder atoms. In this paper, we have synthesized and measured the thermoelectric properties of solid solution CoSbS1-xSex (x = 0, 0.05, 0.10, 0.15, 0.20, 0.30) series samples. The collaborative optimization (enhancing the power factors and reducing the thermal conductivities) to add zT values were realized via substitution of S atoms with the isoelectronic Se atoms in the matrix. Meanwhile, the lowest room temperature lattice thermal conductivity in CoSbS-based materials is obtained (4.72 W m-1 K-1) at present. Benefiting from the results of synergistic strategy, a zT of 0.35 was achieved at 923 K for sample CoSbS0.85Se0.15, a 59% improvement as compared with that of the pristine CoSbS. Band calculation demonstrated that CoSbS0.85Se0.15 present a similar band dispersion with CoSbS. The mechanism of point defect scattering for reducing the lattice thermal conductivity at room temperature, was also analyzed by the Callaway model. The contributions to decrease the room temperature lattice thermal conductivity from the mass and the strain fluctuation in the crystal are comparable. These results can also be extended to other high-efficiency thermoelectric materials with stiff bond and smaller Gruneisen parameters.

Lattice thermal conductivities and thermoelectric performances of binary tin-based sheets: A computational study

Thermal transport properties of nanomaterials are essential for their nanodevices and nano-energy applications. Here, utilizing first-principles calculation with the Boltzmann transport equation, we investigate the lattice thermal conductivities and thermoelectric performances of SnSi and SnGe sheets. Their room-temperature lattice thermal conductivities (κlat) are found in the magnitude of 5–12W/mK, which are smaller than the values in elemental silicene, germanene, and stanene sheets. A long phonon mean free path limitation is found for the SnSi system, which causes a ballistic thermal transport in its finite micro-scale samples, while for the SnGe one, it will still exhibit a diffusive feature instead. Accompanied with the low κlat, their figures of merit are estimated to exceed one in the wide temperature range of 350–800K, where the peak value can arrive at 1.47 and 1.64 for SnSi and SnGe sheets, respectively. Those merits of thermal transport properties will enable intriguing thermoelectric and other sustain-energy applications for binary SnSi and SnGe systems.

Thermoelectric conversion efficiency in IV-VI semiconductors with reduced thermal conductivity

Mid-temperature thermoelectric conversion efficiencies of the IV-VI materials were calculated under the Boltzmann transport theory of carriers, taking the Seebeck, Peltier, and Thomson effects into account. The conversion efficiency was discussed with respect to the lattice thermal conductivity, keeping other parameters such as Seebeck coefficient and electrical conductivity to the same values. If room temperature lattice thermal conductivity is decreased up to 0.5W/mK, the conversion efficiency of a PbS based material becomes as high as 15% with the temperature difference of 500K between 800K and 300K.

Unusual Enhancement in Intrinsic Thermal Conductivity of Multilayer Graphene by Tensile Strains.

Using the Boltzmann-Peierls equation for phonon transport approach with the inputs of interatomic force constants from the self-consistent charge density functional tight binding method, we calculate the room-temperature in-plane lattice thermal conductivities k of multilayer graphene (up to four layers) and graphite under different isotropic tensile strains. The calculated in-plane k of graphite, finite monolayer graphene and 3-layer graphene agree well with previous experiments. For unstrained graphene systems, both the intrinsic k and the extent of the diffusive transport regime present a drastic dimensional transition in going from monolayer to 2-layer graphene and thereafter a gradual transition to the graphite limit. We find a peak enhancement of intrinsic k for multilayer graphene and graphite with increasing strain with the largest enhancement amplitude ∼40%. Competition between the decreased mode heat capacities and the increased lifetimes of flexural phonons with increasing strain contribute to this k behavior. Similar k behavior is observed for 2-layer hexagonal boron nitride systems. This study provides insights into engineering k of multilayer graphene and boron nitride by strain and into the nature of thermal transport in quasi-two-dimensional and highly anisotropic systems.

特異な構造に起因する Fe<sub>2</sub>Al<sub>5</sub> と Fe<sub>4</sub>Al<sub>13</sub> の低格子熱伝導率と熱電材料としての可能性

Iron Aluminide Fe2Al5 has a rigid framework of both fully occupied Al and Fe sites and chains of partially occupied Al sites. On the other hand, Fe4Al13 possesses a large unit cell with 102 atoms. These complex and peculiar crystal structures bring a low lattice thermal conductivity. Here, we report the thermoelectric properties and discuss how the chain structure and large unit cell can lead to a low lattice thermal conductivity. The calculated room-temperature lattice thermal conductivity by using the Wiedemann-Franz law is approximately 1.5 W/mK and 0.8 W/mK for Fe2Al5 and Fe4Al13, respectively. From the comparison with other Fe-Al alloys, which have neither plural partially occupied sites nor a large unit cell, we found that (1) the heat capacity does not decrease at high temperature, i.e. Al atoms at partially occupied sites do not behave as liquid, (2) the speed of sound for Fe2Al5 and Fe4Al13 is almost identical among Fe-Al alloys, i.e. the average phonon group velocity of acoustic modes for Fe2Al5 and Fe4Al13 is not slower than that of Fe-Al alloys, (3) the electrical conductivities of Fe2Al5 and Fe4Al13 are lower than those of the other Fe-Al alloys. These results suggest that the low lattice thermal and electrical conductivities are brought by short relaxation times of both phonons and electrons due to chemical disorder such as the partially occupied sites. In particular, the unit cell of the Fe4Al13 includes 102 atoms, which beneficially reduce the lattice thermal conductivity. The maximum dimensionless figure of merit is approximately 0.02 for both Fe2Al5 and Fe4Al13 at 973 K.

Cu–Bi–Se-based pavonite homologue: a promising thermoelectric material with low lattice thermal conductivity

Pavonite homologues, Cux+yBi5−ySe8 (1.2 ≤ x ≤ 1.5, 0.1 ≤ y ≤ 0.4), in a polycrystalline bulk form have been synthesized using a conventional solid state sintering technique. Their thermal and electronic transport properties were evaluated for mid-temperature thermoelectric power generation applications. Structural complexity, based on unique substitutional and interstitial Cu atoms in the structure, makes this system attractive as an intrinsic low thermal conductivity material; also the band structure calculations revealed that interstitial Cu atoms generate n-type carrier conduction. Room temperature lattice thermal conductivities ranging between 0.41 W m−1 K−1 and 0.55 W m−1 K−1 were found for Cux+yBi5−ySe8; these values are comparable to those of the state-of-the-art low lattice thermal conductivity systems. These extremely low thermal conductivities combined with the power factors result in the highest ZT = 0.27 at 560 K for Cu1.9Bi4.6Se8.

Preparation and thermoelectric properties of sintered n-type K8M8Sn38 (M = Al, Ga and In) with the type-I clathrate structure

The maximum dimensionless figures-of-merit ZTmax were 0.13 at 410 K for K8Al8Sn38, 0.25 at 440 K for K8Ga8Sn38 and 0.21 at 420 K for K8In8Sn38, where their room temperature (RT) mobilities were 4.1 cm2 V−1 s−1, 31.0 cm2 V−1 s−1 and 9.8 cm2 V−1 s−1, respectively, their RT effective masses were 4.3, 1.8 and 3.2 me, respectively, and their RT lattice thermal conductivities were 12 mW cm−1 K−1, 14 mW cm−1 K−1 and 13 mW cm−1 K−1, respectively. The analysis of the measured transport properties suggested that these samples suffered from grain boundary scattering at lower temperatures and from alloy disorder scattering and acoustic phonon scattering at higher temperatures. In particular, such a low mobility of the K8Al8Sn38 sample was considered to be caused by strong alloy disorder scattering. Band structure calculations demonstrated that, in order of K8Ga8Sn38, K8In8Sn38 and K8Al8Sn38, their conduction band edges were sharper and their band structures near the gaps were more similar to that of K8Sn46. These features were well consistent with their measured effective masses and mobilities.

Probing the Lower Limit of Lattice Thermal Conductivity in an Ordered Extended Solid: Gd117Co56Sn112, a Phonon Glass–Electron Crystal System

The discovery of novel materials with low thermal conductivity is paramount to improving the efficiency of thermoelectric devices. As lattice thermal conductivity is inversely linked to unit cell complexity, we set out to synthesize a highly complex crystalline material with glasslike thermal conductivity. Here we present the structure, transport properties, heat capacity, and magnetization of single-crystal Gd(117)Co(56)Sn(112), a complex material with a primitive unit cell volume of ~6858 Å(3) and ~285 atoms per primitive unit cell (1140 atoms per face-centered cubic unit cell). The room temperature lattice thermal conductivity of this material is κ(L) = 0.28 W/(m·K) and represents one of the lowest ever reported for a nonglassy or nonionically conducting bulk solid. Furthermore, this material exhibits low resistivity at room temperature, and thus represents a true physical system that approaches the ideal phonon glass-electron crystal.

Low-temperature structure and lattice dynamics of the thermoelectric clathrate Sn24P19.3I8

The crystal structure of the thermoelectric clathrate Sn24P19.3I8 was determined down to 10K showing no variations with the temperature. Even at 10K Sn24P19.3I8 crystallizes in the type-I clathrate structure, space group Pm3-n, with the cubic unit cell parameter ranging from 10.9173Å at 10K to 10.9554Å at room temperature. In its crystal structure, tin and phosphorus atoms form the framework that traps the guest iodine atoms in the polyhedral cavities of two different shapes. The temperature-dependent crystal structure data and the results of the heat capacity measurements revealed the localized vibrations of the guest atoms inside the oversized cavities with the characteristic Einstein temperatures of θE1=60K and θE2=78K, whereas the characteristic Debye temperature for Sn24P19.3I8 is 265K. The room temperature lattice thermal conductivity was calculated using the Debye model to be κL=0.85Wm−1K−1, which is in excellent agreement with the experimentally measured data and demonstrates that the thermal conductivity is almost entirely phononic.

Preparation and thermoelectric properties of sintered type-I clathrates K8GaxSn46−x

Polycrystalline clathrate samples of nominal K(8)Ga(x)Sn(46-x) were prepared by the spark plasma sintering method to investigate their crystal structures, mobilities and thermoelectric properties. The samples almost had a single-phase type-I clathrate structure, and their relative densities reached as high as 98%. The room-temperature mobility of the K(8)Ga(8)Sn(38) sample was 25 cm(2) V(-1) s(-1), which substantially exceeded the reported mobilities of Rb- and Cs-containing Sn clathrates. Moreover, the mobility was larger than those of the type-I Ba(8)Ga(16)Sn(30), which had more Ga substituting atoms in unit cell. A higher mobility might accordingly be achieved in thermoelectric clathrates with a smaller number of substituting atoms. Their electrical conductivities and Seebeck coefficients in the temperature range 300-450 K were typical of n-type doped semiconductors in the extrinsic region while their room-temperature lattice thermal conductivities were as low as approximately 11 mW cm(-1) K(-1). The maximum dimensionless figure of merit ZT was estimated to be 0.27 at 490 K from the Seebeck coefficient of -262 microV K(-1) and the electrical conductivity of 96 S cm(-1) for the K(8)Ga(8)Sn(38) sample with a carrier concentration of 2.9 x 10(19) cm(-3).

Thermoelectric Properties of the Compounds AgPbmLaTem+2

The thermoelectric properties of the new compounds AgPbmLaTem+2 (m = 15, 18, 20, 25, 30, 35) were investigated in the temperature range of 300 to ∼720 K and compared to those of AgPb18MTe20 (M = Sb, Bi). All samples crystallize in the NaCl-type structure without noticeable secondary phase. The room-temperature electrical conductivities of the AgPbmLaTem+2 samples are >1700 S/cm, which are higher than the Sb or Bi analog. The Seebeck coefficient in the AgPbmLaTem+2 samples ranges from −60 μV/K at 300 K to −160 μV/K at 670 K and is much smaller than the Sb analog, but comparable to the Bi analog. A small Seebeck coefficient is consistent with a high electron concentration of the AgPbmLaTem+2 samples. The corresponding power factors (15−17 μW/(cm K2) at ∼670 K) of the AgPbmLaTem+2 samples are comparable to the Sb analog and higher than the Bi analog. The temperature dependent mobility of the La samples can be expressed through that of n-type degenerate PbTe samples. The derived room temperature lattice thermal conductivities of the AgPbmLaTem+2 samples are <1.4 W/(m K), which are higher than that of the Sb analog (∼0.8 W/(m K)) and are comparable to that of the Bi analog (∼1.2 W/(m K)). A ZT of ∼0.9 at ∼670 K was achieved for the AgPb25LaTe27.

Preparation and thermal conductivities of filled tetrahedral LixIn1−xZnxSb and the related compounds

Abstract Li-filling in tetrahedral InSb and related compounds was attempted to investigate its effect on their thermal conductivities. Li-filled Li 0.2 In 0.8 Zn 0.2 Sb, Li 0.4 In 0.6 Zn 0.4 Sb, LiZnSb, and Li 0.16 Ga 0.84 Zn 0.16 Sb sintered samples were prepared by powder metallurgy. The filled samples had much lower room temperature lattice thermal conductivities than those of the corresponding unfilled materials; the values of the Li 0.4 In 0.6 Zn 0.4 Sb, LiZnSb, and Li 0.16 Ga 0.84 Zn 0.16 Sb were 23, 45, and 72 mW cm −1 K −1 , respectively. Filled tetrahedral compounds such as Li x In 1− x Zn x Sb might be good thermoelectric materials.

Spinodal Decomposition and Nucleation and Growth as a Means to Bulk Nanostructured Thermoelectrics: Enhanced Performance in Pb1-xSnxTe−PbS

The solid-state transformation phenomena of spinodal decomposition and nucleation and growth are presented as tools to create nanostructured thermoelectric materials with very low thermal conductivity and greatly enhanced figure of merit. The systems (PbTe)(1-x)(PbS)(x) and (Pb(0.95)Sn(0.05)Te)(1-x)(PbS)(x) are not solid solutions but phase separate into PbTe-rich and PbS-rich regions to produce coherent nanoscale heterogeneities that severely depress the lattice thermal conductivity. For x > approximately 0.03 the materials are ordered on three submicrometer length scales. Transmission electron microscopy reveals both spinodal decomposition and nucleation and growth phenomena the relative magnitude of which varies with x. We show that the (Pb(0.95)Sn(0.05)Te)(1-x)(PbS)(x) system, despite its nanostructured nature, maintains a high electron mobility (>100 cm(2)/V x s at 700 K). At x approximately 0.08 the material achieves a very low room-temperature lattice thermal conductivity of approximately 0.4 W/m x K. This value is only 28% of the PbTe lattice thermal conductivity at room temperature. The inhibition of heat flow in this system is caused by nanostructure-induced acoustic impedance mismatch between the PbTe-rich and PbS-rich regions. As a result the thermoelectric properties of (Pb(0.95)Sn(0.05)Te)(1-x)(PbS)(x) at x = 0.04, 0.08, and 0.16 were found to be superior to those of PbTe by almost a factor of 2. The relative importance of the two observed modes of nanostructuring, spinodal decomposition and nucleation and growth, in suppressing the thermal conductivity was assessed in this work, and we can conclude that the latter mode seems more effective in doing so. The promise of such a system for high efficiency is highlighted by a ZT approximately 1.50 at 642 K for x approximately 0.08.

Structure and Raman scattering study on Ba 8Ga xSi 46− x ( x=10 and 16) type I clathrates

Structure and vibrational properties of Ba 8Ga x Si 46− x ( x=10 and 16) clathrates were studied by X-ray diffraction and Raman scattering measurements. The temperature dependent electrical resistivity measurement on Ba 8Ga 10Si 36 has shown semiconducting nature of that clathrate with an energy band gap value of 0.31 eV. On the other hand the measurement on Ba 8Ga 16Si 30 has shown metallic like electrical conductivity of that clathrate. The origin of semiconductivity in Ba 8Ga 10Si 36 was found to be due to the vacancy disorder in the framework sites. Room temperature Raman scattering measurements resolved several Raman vibrational modes, including low frequencies ones corresponding to the rattling motion of Ba atoms. The low frequency positions of Ba in the respective clathrates at 49.4, 73.7 and 97.3 cm −1 for Ba 8Ga 10Si 36 and at 43.7, 74.5 and 92.4 cm −1 for Ba 8Ga 16Si 30 were found to be in agreement with the reported density functional (DF) calculated low frequency modes of Ba 8Ga 16Si 30. The framework gallium difference and vacancy disorders were found to influence the position and widths of frequency modes. Room temperature lattice thermal conductivity of Ba 8Ga 10Si 36 and Ba 8Ga 16Si 30 were 1.128 and 1.071 Wm −1 K −1, respectively, and this low value was attributed to the resonant scattering between the framework acoustic and Ba rattling modes.

Composition and Properties of Layered Compounds in the GeTe–Sb2Te3System

The 620-K section of the Ge–Sb–Te phase diagram was mapped out using x-ray diffraction, microstructural analysis, and microhardness measurements. The transport properties of the layered tetradymite-like compounds nGeTe · mSb2Te3(n, m= 1–4) were studied in wide temperature ranges (Hall effect and electrical resistivity, from 77 to 800 K, and thermoelectric power, from 90 to 450 K). The results show that the nGeTe · mSb2Te3compounds are degeneratep-type semiconductors with a fairly high hole concentration due to the high density of intrinsic point defects. The temperature dependences of the Hall coefficient and resistivity exhibit anomalies related to solid-state phase transitions. The room-temperature lattice thermal conductivity ofnGeTe · mSb2Te3is fairly low, in the range 8–10 mW/(cm K).

Connections between Crystallographic Data and New Thermoelectric Compounds

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 and the Lattice Thermal Conductivity of Clathrate-like Thermoelectric Compounds

A new structure–property relationship links atomic displacement parameters (ADP) 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. X-ray crystallography data, reported in the literature, are used to apply this analysis to several promising classes of thermoelectric materials.

Preparation and thermoelectric properties of semiconducting Zn 4Sb 3

Hot-pressed samples of the semiconducting compound β-Zn 4Sb 3 were prepared and characterized by X-ray and microprobe analysis. Some physical properties of β-Zn 4Sb 3 were determined and its thermoelectric properties measured between room temperature and 650 K. Exceptionally low thermal conductivity values were obtained in the 300–650 K temperature range and the room temperature lattice thermal conductivity was estimated at 6.5 W cm −1 K −1. High thermoelectric figures of merit ( ZTs) were obtained between 450 and 670 K and a maximum of about 1.3 was obtained at a temperature of 670 K, the highest known at this temperature. The stability of the compound was investigated by several techniques, including thermogravimetric studies. The results showed that the samples were stable under argon atmosphere and static vacuum up to about 670 K and up to 520 K in dynamic vacuum. The high thermoelectric performance of β-Zn 4Sb 3 in the 300–670 K temperature range fills the existing gap in the ZT spectrum of p-type state-of-the-art thermoelectric materials between Bi 2Te 3-based alloys and PbTe-based alloys. This material, relatively inexpensive, could be used in more efficient thermoelectric generators for waste heat recovery and automobile industry applications, for example.

Calculation of the lattice thermal conductivity in GaAs-InAs alloys and comparison with experiment

The room-temperature lattice thermal conductivity of GaAs-InAs alloys is calculated and compared to recently measured thermal conductivity of GaAs dilutely alloyed with InAs [M. C. Ohmer, W. C. Mitchel, G. A. Graves, D. E. Holmes, H. Kuwamoto, and P. W. Yu, J. Appl. Phys. 64, 2775 (1988)] and with older data at higher concentrations. Our calculation considers both the normal and Umklapp anharmonic interaction, as well as mass differences and size distortions for the scattering by point defects. The results indicate that it is the size-distortion scattering which leads to a very abrupt decrease in the thermal conductivity for dilute alloys. The theory of Klemens and Callaway used in the present work is in semiquantitative agreement with experiments, consistent with both the experimental and theoretical uncertainties. Unlike previous calculations, we were able to reproduce a very sharp decline in the thermal conductivity upon alloying for very dilute alloys.

Calculation of room temperature lattice thermal conductivity of several materials using a continuum model

The lattice thermal conductivities at 300°K of Ge, Si, GaAs, MgO, NaCl and KCl have been calculated using a method which starts from the second and third order elastic constants.