Thermal properties of high quality single crystals of bismuth telluride—Part II: Mixed-scattering model
TL;DR: In this paper, a mixed-scattering model was used to fit the sharp variations of the various parameters with stoichiometric deviations, and the optimum Fermi level for the maximum of the figure of merit was found just at the bottom of the conduction band.
About: This article is published in Journal of Physics and Chemistry of Solids.The article was published on 1988-01-01. It has received 26 citations till now. The article focuses on the topics: Fermi level & Effective mass (solid-state physics).
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TL;DR: In this paper, the authors identify and quantify the key material properties that make Bi2Te3 such a good thermoelectric material, which can be used for benchmarking future improvements in Bi2TE3 or new replacement materials.
Abstract: DOI: 10.1002/aelm.201800904 made for efficient thermoelectric cooling or temperature management uses Bi2Te3 alloys. Such solid-state devices dominate the market for temperature control in optoelectronics. As the need to eliminate greenhouse-gas refrigerants increases, Peltier cooling is becoming more attractive particularly in small systems where efficiencies are comparable to traditional refrigerant based cooling. Such small devices may enable distributive heating/ cooling (only where and when it is needed) with higher system level energy efficiency, for example in electric vehicles where energy for heating/cooling competes with vehicle range. Even for thermoelectric power generation, e.g., recovery of waste heat, Bi2Te3 alloys are most used because of superior efficiency up to 200 °C and the technology to make devices with Bi2Te3 is most advanced.[1–3] While the material and production technology for making Bi2Te3-based devices has remained essentially unchanged since the 1960s, our understanding of these materials has advanced considerably. Most recently, the interest in topological insulators (TI) has led to new insights into the complex electronic structure[4,5] revealing that with the accuracy in assessing the band structures available today, improvements in the electronic structure by band engineering should not only be possible but predictable.[6–9] Indeed, the p-type alloys chosen for use in commercial Peltier coolers appear to have unintentionally arrived at a composition close to a band convergence. The understanding of defects and doping is also advancing rapidly that will lead to new strategies for additional improvements in the electronic properties. The thermal conductivity of Bi2Te3-based alloys can also be engineered, where in particular there is much recent interest in microstructure engineering or nanostructuring.[10–22] Reduced thermal conductivity has led to numerous reports of exceptionally high efficiency (zT) that would be sufficient to revolutionize the industry. However, between measurement and material uncertainties, a revolutionary new Bi2Te3-based material has not made it to the market. Because even small but reliable improvements could make significant impact, it is worthwhile to better understand all the complex, interdependent effects of band engineering and microstructure engineering. To demonstrate and quantify improvements in thermoelectric properties, it is necessary to have well characterized properties or reliable benchmarks for comparison. Bismuth telluride is the working material for most Peltier cooling devices and thermoelectric generators. This is because Bi2Te3 (or more precisely its alloys with Sb2Te3 for p-type and Bi2Se3 for n-type material) has the highest thermoelectric figure of merit, zT, of any material around room temperature. Since thermoelectric technology will be greatly enhanced by improving Bi2Te3 or finding a superior material, this review aims to identify and quantify the key material properties that make Bi2Te3 such a good thermoelectric. The large zT can be traced to the high band degeneracy, low effective mass, high carrier mobility, and relatively low lattice thermal conductivity, which all contribute to its remarkably high thermoelectric quality factor. Using literature data augmented with newer results, these material parameters are quantified, giving clear insight into the tailoring of the electronic band structure of Bi2Te3 by alloying, or reducing thermal conductivity by nanostructuring. For example, this analysis clearly shows that the minority carrier excitation across the small bandgap significantly limits the thermoelectric performance of Bi2Te3, even at room temperature, showing that larger bandgap alloys are needed for higher temperature operation. Such effective material parameters can also be used for benchmarking future improvements in Bi2Te3 or new replacement materials.
350 citations
01 Jan 1995
TL;DR: In this paper, the ZT for PGEC relaxation of A,,.34.4.4 Introduction Systematic Search Historical Review New Materials Phonon "Glasses" Desired Performance PGEC Relaxation of A,.
Abstract: 34.4 Introduction Systematic Search Historical Review New Materials Phonon "Glasses" Desired Performance PGEC Relaxation of A,,. Assumption Band Gaps of Semiconductors Carrier Mobilities Background Explanation Electronegativities and Good Thermoelectric Semiconductors Dopant and Mixed-Crystal Effects on Mobilities Dopant Effects on the Weighted Mobility Mixed-Crystal Effects on Mobility Weighted Mobility Lattice Thermal Conductivity Phonon Scattering Mechanisms New Amin Crystals and New Thermoelectrics Conclusions From the Analysis Appendix: Calculation of ZT for PGEC References
341 citations
TL;DR: The uniformity and high yield of the nanowires provide a promising route to make significant contributions to the manufacture of nanotechnology-based thermoelectric power generation and solid-state cooling devices with superior performance in a reliable and a reproducible way.
Abstract: A rational yet scalable solution phase method has been established, for the first time, to obtain n-type Bi2Te3 ultrathin nanowires with an average diameter of 8 nm in high yield (up to 93%). Thermoelectric properties of bulk pellets fabricated by compressing the nanowire powder through spark plasma sintering have been investigated. Compared to the current commercial n-type Bi2Te3-based bulk materials, our nanowire devices exhibit an enhanced ZT of 0.96 peaked at 380 K due to a significant reduction of thermal conductivity derived from phonon scattering at the nanoscale interfaces in the bulk pellets, which corresponds to a 13% enhancement compared to that of the best n-type commercial Bi2Te2.7Se0.3 single crystals (∼0.85) and is comparable to the best reported result of n-type Bi2Te2.7Se0.3 sample (ZT = 1.04) fabricated by the hot pressing of ball-milled powder. The uniformity and high yield of the nanowires provide a promising route to make significant contributions to the manufacture of nanotechnology-...
281 citations
TL;DR: In this article, the thermoelectric properties and crystal structure of individual electrodeposited bismuth telluride nanowires (NWs) were characterized using a microfabricated measurement device and transmission electron microscopy.
Abstract: The thermoelectric properties and crystal structure of individual electrodeposited bismuth telluride nanowires (NWs) were characterized using a microfabricated measurement device and transmission electron microscopy. Annealing in hydrogen was used to obtain electrical contact between the NW and the supporting Pt electrodes. By fitting the measured Seebeck coefficient with a two-band model, the NW samples were determined to be highly n-type doped. Higher thermal conductivity and electrical conductivity were observed in a 52 nm diameter monocrystalline NW than a 55 nm diameter polycrystalline NW. The electron mobility of the monocrystalline NW was found to be about 19% lower than that of bulk crystal at a similar carrier concentration and about 2.5 times higher than that of the polycrystalline NW. The specularity parameter for electron scattering by the NW surface was determined to be about 0.7 and partially specular and partially diffuse, leading to a reduction in the electron mean-free path from 61 nm in ...
165 citations
TL;DR: In this article, single crystal solid solutions with compositions Bi 8 Sb 32 Te 60, Bi 9 Sb 31 Te 60 and Bi 10 Sb 30 Te 60 were grown using the Traveling Heater Method (T.H.M.).
157 citations
References
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TL;DR: In this article, the phase diagram in the region about the cleavage planes was clarified and the lattice conductivity was attributed to transport of energy by ambipolar diffusion of electrons and holes.
Abstract: Samples of both $n$-type and $p$-type ${\mathrm{Bi}}_{2}$${\mathrm{Te}}_{3}$ containing from 3\ifmmode\times\else\texttimes\fi{}${10}^{17}$ to 5\ifmmode\times\else\texttimes\fi{}${10}^{19}$ extrinsic carriers were prepared and the phase diagram in the region about ${\mathrm{Bi}}_{2}$${\mathrm{Te}}_{3}$ has been clarified. The Hall mobility parallel to the cleavage planes varies as ${T}^{\ensuremath{-}1.5}$ for holes and ${T}^{\ensuremath{-}2.7}$ for electrons. Room temperature values are ${\ensuremath{\mu}}_{p}=420$ ${\mathrm{cm}}^{2}$ ${\mathrm{v}}^{\ensuremath{-}1}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ and ${\ensuremath{\mu}}_{n}=270$ ${\mathrm{cm}}^{2}$ ${\mathrm{v}}^{\ensuremath{-}1}$ ${\mathrm{sec}}^{\ensuremath{-}1}$. The energy gap is ${E}_{g}=0.20$ electron volts. From thermal conductivity measurements over the temperature range from 77\ifmmode^\circ\else\textdegree\fi{}K to 380\ifmmode^\circ\else\textdegree\fi{}K the lattice conductivity was found to be ${\ensuremath{\kappa}}_{L}=5.10\ifmmode\times\else\texttimes\fi{}\frac{{10}^{\ensuremath{-}2}}{T}$ watt-${\mathrm{deg}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$. The sharp rise in the thermal conductivity in the vicinity of room temperature was attributed to transport of energy by ambipolar diffusion of electrons and holes.
380 citations
TL;DR: In this paper, the authors examined the high-temperature thermoelectric energy-conversion theory and showed that semiconductors are the logical choices for high-figure of merit-value materials, but the requirements for optimization differ depending on whether the material is classed as a broadband or narrowband semiconductor.
23 citations