CsBi4Te6: A High-Performance Thermoelectric Material for Low-Temperature Applications (original) (raw)
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A New Thermoelectric Material: CsBi 4 Te 6
Journal of the American Chemical Society, 2004
The highly anisotropic material CsBi4Te6 was prepared by the reaction of Cs/Bi2Te3 around 600°C . The compound crystallizes in the monoclinic space group C2/m with a ) 51.9205(8) Å, b ) 4.4025(1) Å, c ) 14.5118(3) Å, ) 101.480(1)°, V ) 3250.75(11) Å 3 , and Z ) 8. The final R values are R1 ) 0.0585 and wR2 ) 0.1127 for all data. The compound has a 2-D structure composed of NaCl-type [Bi4Te6] anionic layers and Cs + ions residing between the layers. The [Bi4Te6] layers are interconnected by Bi-Bi bonds at a distance of 3.2383(10) Å. This material is a narrow gap semiconductor. Optimization studies on the thermoelectric properties with a variety of doping agents show that the electrical properties of CsBi4Te6 can be tuned to yield an optimized thermoelectric material which is promising for low-temperature applications. SbI3 doping resulted in p-type behavior and a maximum power factor of 51.5 µW/cm‚K 2 at 184 K and the corresponding ZT of 0.82 at 225 K. The highest power factor of 59.8 µW/cm‚K 2 at 151 K was obtained from 0.06% Sb-doped material. We report here the synthesis, physicochemical properties, doping characteristics, charge-transport properties, and thermal conductivity. Also presented are studies on n-type CsBi4Te6 and comparisons to those of p-type. Hogan, T.; Schindler, J.; Iordanidis, L.; Brazis, P.; Kannewurf, C. R.; Chen, B.; Uher, C.; Kanatzidis, M. G. In Materials Iordanidis, L.; Schindler, J. L.; Brazis, P. W.; Kannewurf, C. R.; Chen, B.; Hu, S.; Uher, C.; Kanatzidis, M. G. Chem.
New promising bulk thermoelectrics: intermetallics, pnictides and chalcogenides
The European Physical Journal B, 2014
The need of alternative "green" energy sources has recently renewed the interest in thermoelectric (TE) materials, which can directly convert heat to electricity or, conversely, electric current to cooling. The thermoelectric performance of a material can be estimated by the so-called figure of merit, zT = σα 2 T /λ (α the Seebeck coefficient, σα 2 the power factor, σ and λ the electrical and thermal conductivity, respectively), that depends only on the material. In the middle 1990s the "phonon glass and electron crystal" concept was developed, which, together with a better understanding of the parameters that affect zT and the use of new synthesis methods and characterization techniques, has led to the discovery of improved bulk thermoelectric materials that start being implemented in applications. During last decades, special focus has been made on skutterudites, clathrates, half-Heusler alloys, Si1−xGex-, Bi2Te3and PbTe-based materials. However, many other materials, in particular based on intermetallics, pnictides, chalcogenides, oxides, etc. are now emerging as potential advanced bulk thermoelectrics. Herein we discuss the current understanding in this field, with special emphasis on the strategies to reduce the lattice part of the thermal conductivity and maximize the power factor, and review those new potential thermoelectric bulk materials, in particular based on intermetallics, pnictides and chalcogenides. A final chapter, discussing different shaping techniques leading to bulk materials (eventually from nanostructured TE materials), is also included.
High performance n-type (Bi,Sb)2(Te,Se)3 for low temperature thermoelectric generator
Journal of Physics D-applied Physics, 2010
Starting with elemental chunks of bismuth, antimony, tellurium and selenium, densified bulk materials (Bi 0.95 Sb 0.05 ) 2 (Te 1−x Se x ) 3 (x = 0.10, 0.13, 0.15 and 0.17) were prepared by melt spinning subsequently combined with a spark plasma sintering process. The prepared bulk materials display fine grain size and numerous layered structures with a size of 10-100 nm; moreover, details of the composition difference and phase difference cannot be observed. Measurements of electrical conductivity, Seebeck coefficient and thermal conductivity have been performed in the temperature range 300-500 K, and it is found that the thermoelectric properties are significantly affected by the content of selenium. All the prepared samples show higher ratios of electrical conductivity and total thermal conductivity compared with state-of-the-art commercial zone melted materials, mainly a large reduction in lattice thermal conductivity, which is more beneficial to the concept of 'electron crystal phonon glass'. Subsequently, the resulting thermoelectric figure of merit ZT value reaches a maximum of 1.0 at 460 K for the n-type (Bi 0.95 Sb 0.05 ) 2 (Te 0.85 Se 0.15 ) 3 bulk material. Compared with traditional zone melted materials, the peak ZTs move towards a higher temperature and this study demonstrates the possibility of preparing materials with high performance, which can be applied for low temperature power generation or multi-stage devices.
Bi 2 Te 3-based compounds have long been studied as thermoelectric materials in cooling applications near room temperature. Here, we investigated the thermoelectric properties of CuI-doped Bi 2 Te 2.1 Se 0.9 compounds. The Cu/I codoping induces the lattice distortion partially in the matrix. We report that the charge density wave caused by the local lattice distortion affects the electrical and thermal transport properties. From the high-temperature specific heat, we found a first-order phase transitions near 490 and 575 K for CuI-doped compounds (CuI) x Bi 2 Te 2.1 Se 0.9 (x = 0.3 and 0.6%), respectively. It is not a structural phase transition, confirming from the high-temperature X-ray diffraction. The temperature-dependent electrical resistivity shows a typical behavior of charge density wave transition, which is consistent with the temperature-dependent Seebeck coefficient and thermal conductivity. The transmission electron microscopy and electron diffraction show a local lattice distortion, driven by the charge density wave transition. The charge density wave formation in the Bi 2 Te 3-based compounds are exceptional because of the possibility of coexistence of charge density wave and topological surface states. From the Kubo formula and Boltzmann transport calculations, the formation of charge density wave enhances the power factor. The lattice modulation and charge density wave decrease lattice thermal conductivity, resulting in the enhancement of thermoelectric performance simultaneously in CuI-doped samples. Consequently, an enhancement of thermoelectric performance ZT over 1.0 is achieved at 448 K in the (CuI) 0.003 Bi 2 Te 2.1 Se 0.9 sample. The enhancement of ZT at high temperature gives rise to a superior average ZT avg (1.0) value than those of previously reported ones.
Physical Review Applied
Deeper understanding of electrical and thermal transport is critical for further development of thermoelectric materials. Here we describe the thermoelectric performance of a group of rare-earth-bearing half-Heusler phases determined in a wide temperature range. Polycrystalline samples of ScNiSb, DyNiSb, ErNiSb, TmNiSb, and LuNiSb are synthesized by arc melting and densified by spark plasma sintering. They are characterized by powder x-ray diffraction and scanning electron microscopy. The physical properties are studied by means of heat-capacity and Hall-effect measurements performed in the temperature range from 2 to 300 K, as well as electrical-resistivity, Seebeck-coefficient, and thermal-conductivity measurements performed in the temperature range from 2 to 950 K. All the materials except TmNiSb are found to be narrow-gap intrinsic p-type semiconductors with rather light charge carriers. In TmNiSb, the presence of heavy holes with large weighted mobility is evidenced by the highest power factor among the series (17 μW K −2 cm −1 at 700 K). The experimental electronic relaxation time calculated with the parabolic band formalism is found to range from 0.8 × 10 −14 to 2.8 × 10 −14 s. In all the materials studied, the thermal conductivity is between 3 and 6 W m −1 K −1 near room temperature (i.e., smaller than in other pristine d-electron half-Heusler phases reported in the literature). The experimental observation of the reduced thermal conductivity appears fully consistent with the estimated low sound velocity as well as strong point-defect scattering revealed by Debye-Callaway modeling. Furthermore, analysis of the bipolar contribution to the measured thermal conductivity yields abnormally large differences between the mobilities of n-type and p-type carriers. The latter feature makes the compounds examined excellent candidates for further optimization of their thermoelectric performance via electron doping.
Solution-Based Synthesis and Low-Temperature Transport Properties of CsBi4Te6
ACS Applied Materials & Interfaces, 2012
The thermoelectric material CsBi 4 Te 6 was synthesized in nanometer thin flake-like form by a low temperature solvothermal approach. The crystals were then densified by spark plasma sintering (SPS), resulting in a polycrystalline specimen with layered and partially orientated grains. The orientation of the CsBi 4 Te 6 flakes reflects the anisotropic crystal structure of the material aided by the unidirectional pressure during SPS. Hall, resistivity, Seebeck coefficient, and thermal conductivity was measured on the polycrystalline specimen in evaluating the potential of this approach for thermoelectric applications.
Applied Physics Letters, 2011
The electronic band structures of Ce 3 Te 4 have been studied using the first-principles density-functional theory calculations. It is found that the density of states of Ce 3 Te 4 has a very high delta-shaped peak appearing 0.21 eV above the Fermi level, which mainly comes from the f orbital electrons of the rare-earth element Ce. Using the simple theory proposed by Mahan and Sofo, ͓Proc. Natl. Acad. Sci. U.S.A. 93, 7436 ͑1996͔͒, we obtain an ideal value of zT= 13.5 for Ce 3 Te 4 at T = 1200 K, suggesting that the rare-earth chalcogenide Ce 3 Te 4 could be a promising high efficiency high temperature thermoelectric material.