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Yuping He, Catalin D Spataru, Francois Léonard, Reese E Jones, Michael E Foster, Mark D Allendorf, A Alec Talin
Two-dimensional (2D) materials have attracted much attention due to their novel properties. An exciting new class of 2D materials based on metal-organic frameworks (MOFs) has recently emerged, displaying high electrical conductivity, a rarity among organic nanoporous materials. The emergence of these materials raises intriguing questions about their fundamental electronic, optical, and thermal properties, but few studies exist in this regard. Here we present an atomistic study of the thermoelectric properties of crystalline 2D MOFs X3(HITP)2 with X = Ni, Pd or Pt, and HITP = 2,3,6,7,10,11-hexaiminotriphenylene, using both ab initio transport models and classical molecular dynamics simulations...
July 18, 2017: Physical Chemistry Chemical Physics: PCCP
Xiaoliang Zeng, Yucheng Xiong, Qiang Fu, Rong Sun, Jianbin Xu, Dongyan Xu, Ching-Ping Wong
The ability to control thermal conductivity is important in a wide variety of applications, especially in heat removal, heat insulation, and thermoelectric energy conversion. Herein, we reveal that the thermal conductivity of epoxy resin fibers increases on decreasing the fiber diameter and surpasses the bulk value (0.25 W m(-1) K(-1) at 300 K) for the fiber with a diameter of 211 nm. The variation of thermal conductivity in epoxy resin fibers can likely be attributed to their microstructure change-enhanced interface phonon scattering between amorphous and crystalline regions and the enhanced alignment of the molecular chain orientation...
July 17, 2017: Nanoscale
Yong Kyu Lee, Kyunghan Ahn, Joonil Cha, Chongjian Zhou, Hyo Seok Kim, Garam Choi, Sue In Chae, Jae-Hyuk Park, Yeseul Lee, Cheol-Hee Park, Sung-Pyo Cho, Sang Hyun Park, Yung-Eun Sung, Won Bo Lee, Taeghwan Hyeon, In Chung
SnSe emerges as a new class of thermoelectric materials since recent discovery of an ultrahigh thermoelectric figure of merit in its single crystals. Achieving such performance in the polycrystalline counterpart is still challenging and requires fundamental understandings of its electrical and thermal transport properties as well as structural chemistry. Here we demonstrate a new strategy of improving conversion efficiency of bulk polycrystalline SnSe thermoelectrics. We show that PbSe alloying decreases the transition temperature between Pnma and Cmcm phases and thereby can serve as a means of controlling its onset temperature...
July 14, 2017: Journal of the American Chemical Society
Xingang Zhao, Deepa Madan, Yan Cheng, Jiawang Zhou, Hui Li, Susanna M Thon, Arthur E Bragg, Mallory E DeCoster, Patrick E Hopkins, Howard E Katz
Air-stable and soluble tetrabutylammonium fluoride (TBAF) is demonstrated as an efficient n-type dopant for the conjugated polymer ClBDPPV. Electron transfer from F(-) anions to the π-electron-deficient ClBDPPV through anion-π electronic interactions is strongly corroborated by the combined results of electron spin resonance, UV-vis-NIR, and ultraviolet photoelectron spectroscopy. Doping of ClBDPPV with 25 mol% TBAF boosts electrical conductivity to up to 0.62 S cm(-1) , among the highest conductivities that have been reported for solution-processed n-type conjugated polymers, with a thermoelectric power factor of 0...
July 14, 2017: Advanced Materials
Bobo Shi, Hetao Su, Jinshi Li, Haining Qi, Fubao Zhou, José L Torero, Zhongwei Chen
The coal fires, a global catastrophe for hundreds of years, have been proved extremely difficult to control, and hit almost every coal-bearing area globally. Meanwhile, underground coal fires contain tremendous reservoir of geothermal energy. Approximately one billion tons of coal burns underground annually in the world, which could generate ~1000 GW per annum. A game-changing approach, environmentally sound thermal energy extraction from the intractable natural coalfield fires, is being developed by utilizing the waste energy and reducing the temperature of coalfield fires at the same time...
July 13, 2017: Scientific Reports
Stefan Maier, Olivier Perez, Denis Pelloquin, David Berthebaud, Sylvie Hébert, Franck Gascoin
Single-crystal and polycrystalline Ba4Cu8Se13 were synthesized; the average crystal structure was solved by single-crystal X-ray diffraction, and the structural model was confirmed by a detailed electron microscopy study of polycrystalline Ba4Cu8Se13. The title compound can be rationalized as (Ba(2+))4(Cu(+))8(Se(2-))2(Se2(2-))4(Se3(4-)) and crystallizes in a new structure type (space group C2/c with a = 9.171(8) Å, b = 9.146(8) Å, c = 27.35(3) Å, β = 93.21(3)°, and V = 2291 Å(3)). It contains unprecedented Cu4Se9 fragments with planar Cu rectangles...
July 13, 2017: Inorganic Chemistry
Hatef Sadeghi, Sara Sangtarash, Colin J Lambert
Recent advances in the engineering of pico-scale gaps between electroburnt graphene electrodes provide new opportunities for studying electron transport through electrostatically-gated single molecules. But first we need to understand and develop strategies for anchoring single molecules to such electrodes. Here, for the first time, we present a systematic theoretical study of transport properties using four different modes of anchoring zinc-porphyrin monomer, dimer and trimer molecular wires to graphene electrodes...
July 12, 2017: Nano Letters
Hanyu Jia, Zhaoyang Ju, Xinglei Tao, Xiao-Qian Yao, Yapei Wang
An intriguing p-n conversion of thermoelectric property was observed in a water-ionic liquid ([EMIm][Ac]) binary system with precise control over water content. The highest p-type and n-type Seebeck coefficient were optimized at water-[EMIm][Ac] molar ratio of 2:1 and 4:1, respectively. DFT calculation illustrates that a configuration of solvent separation ion pairs is preferred at the water-[EMIm][Ac] molar ratio of 4:1, leading to the p-n conversion through weakening interaction between anion clusters and gold electrodes...
July 12, 2017: Langmuir: the ACS Journal of Surfaces and Colloids
Jaeyoo Choi, Yeonsu Jung, Seung Jae Yang, Jun Young Oh, Jinwoo Oh, Kiyoung Jo, Jeong Gon Son, Seung Eon Moon, Chong Rae Park, Heesuk Kim
As practical interest in flexible/or wearable power-conversion devices increases, the demand for high-performance alternatives to thermoelectric (TE) generators based on brittle inorganic materials is growing. Herein, we propose a flexible and ultralight TE generator (TEG) based on carbon nanotube yarn (CNTY) with excellent TE performance. The as-prepared CNTY shows a superior electrical conductivity of 3147 S/cm due to increased longitudinal carrier mobility derived from highly-aligned structure. Our TEG is innovative in that the CNTY acts as multi-functions in the same device...
July 12, 2017: ACS Nano
Biplab Paul, Jun Lu, Per Eklund
Due to their inherent rigidity and brittleness, inorganic materials have seen limited use in flexible thermoelectric applications. On the other hand, for high output power density and stability, the use of inorganic materials is required. Here, we demonstrate a concept of fully-inorganic flexible thermoelectric thin films with Ca3Co4O9-on-mica. Ca3Co4O9 is promising not only due to its high Seebeck coefficient and good electrical conductivity but also important due to the abundance, low cost and nontoxicity of its constituent raw materials...
July 12, 2017: ACS Applied Materials & Interfaces
Peter Samuelsson, Sara Kheradsoud, Björn Sothmann
We show theoretically that a thermoelectric heat engine, operating exclusively due to quantum-mechanical interference, can reach optimal linear-response performance. A chiral edge state implementation of a close-to-optimal heat engine is proposed in an electronic Mach-Zehnder interferometer with a mesoscopic capacitor coupled to one arm. We demonstrate that the maximum power and corresponding efficiency can reach 90% and 83%, respectively, of the theoretical maximum. The proposed heat engine can be realized with existing experimental techniques and has a performance robust against moderate dephasing...
June 23, 2017: Physical Review Letters
Tianhua Zou, Tiantian Jia, Wenjie Xie, Yongsheng Zhang, Marc Widenmeyer, Xingxing Xiao, Anke Weidenkaff
Doping (or substitution)-induced modification of the electronic structure to increase the electronic density of states (eDOS) near the Fermi level is considered as an effective strategy to enhance the Seebeck coefficient, and may consequently boost the thermoelectric performance. Through density-functional theory calculations of Mn-substituted TiFe2-xMnxSn compounds, we demonstrate that the d-states of the substituted Mn atoms induce a strong resonant level near the Fermi energy. Our experimental results are in good agreement with the calculations...
July 11, 2017: Physical Chemistry Chemical Physics: PCCP
Xixia Kong, Wei Zhu, Lili Cao, Yuncheng Peng, Shengfei Shen, Yuan Deng
The contact resistance between metals and semiconductors has become critical for the design of thin-film thermoelectric devices with their continuous miniaturization. Herein, we report a novel interface tuning method to regulate the contact resistance at the Bi2Te3-Cu interface, and three Bi2Te3 films with different oriented microstructures are obtained. The lowest contact resistivity (∼10(-7) Ω cm(2)) is observed between highly (00l) oriented Bi2Te3 and Cu film, nearly an order of magnitude lower than other orientations...
July 19, 2017: ACS Applied Materials & Interfaces
Michał Falkowski, Andre M Strydom
The results of the magnetic, electron transport, heat capacity and heat conduction measurements on the new rhombohedral ternary compound Pr<sub>2</sub>Rh<sub>3</sub>Ge have been investigated. The synthesized polycrystalline compound was found to crystallize in the ternary ordered variant of the cubic Laves phase MgCu<sub>2</sub>-type of structure with the space group <i>R</i>-3<i>m</i>, as previously reported. Pr<sub>2</sub>Rh<sub>3</sub>Ge exhibits a ferromagnetic behaviour below T<sub>C</sub> = 8...
July 6, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Yanguang Zhou, Xiaojing Gong, Ben Xu, Ming Hu
Thermoelectric (TE) materials manifest themselves to enable direct conversion of temperature differences to electric power and vice versa. Though remarkable advances have been achieved in the past decades for various TE systems, the energy conversion efficiency of TE devices, which is characterized by a dimensionless figure-of-merit (ZT = S(2)σT/(κel + κph)), generally remains a poor factor that severely limits TE devices' competitiveness and range of employment. The bottleneck for substantially boosting the ZT coefficient lies in the strong interdependence of the physical parameters involved in electronic (S and σ, and κel) and phononic (κph) transport...
July 6, 2017: Nanoscale
C Yang, D Souchay, M Kneiß, M Bogner, H M Wei, M Lorenz, O Oeckler, G Benstetter, Y Q Fu, M Grundmann
Thermoelectric devices that are flexible and optically transparent hold unique promise for future electronics. However, development of invisible thermoelectric elements is hindered by the lack of p-type transparent thermoelectric materials. Here we present the superior room-temperature thermoelectric performance of p-type transparent copper iodide (CuI) thin films. Large Seebeck coefficients and power factors of the obtained CuI thin films are analysed based on a single-band model. The low-thermal conductivity of the CuI films is attributed to a combined effect of the heavy element iodine and strong phonon scattering...
July 6, 2017: Nature Communications
Sol Kim, Man Young Lee, Seong Lee, Seung-Hoon Jhi
Discovering the materials that have work functions less than 1 eV is essential for efficient thermionic energy converter (TEC). The lowest work function of materials reported so far is in a range of about 1 eV. Here, to design low work function materials, we perform first-principles calculations on selected materials of transition metal dichalcogenide as substrates and alkali metals as adsorbates. The work function of our selected materials has a dip ubiquitously independent of the true binding distances of the adsorbates and exhibits contrasting behavior between empty d-shell elements (K, Rb, and Cs) and the others (Li and Na)...
July 6, 2017: Journal of Physics. Condensed Matter: An Institute of Physics Journal
Tursun Ablekim, Santosh K Swain, Wan-Jian Yin, Katherine Zaunbrecher, James Burst, Teresa M Barnes, Darius Kuciauskas, Su-Huai Wei, Kelvin G Lynn
Efficient p-type doping in CdTe has remained a critical challenge for decades, limiting the performance of CdTe-based semiconductor devices. Arsenic is a promising p-type dopant; however, reproducible doping with high concentration is difficult and carrier lifetime is low. We systematically studied defect structures in As-doped CdTe using high-purity single crystal wafers to investigate the mechanisms that limit p-type doping. Two As-doped CdTe with varying acceptor density and two undoped CdTe were grown in Cd-rich and Te-rich environments...
July 4, 2017: Scientific Reports
J Zhang, H J Liu, L Cheng, J Wei, J H Liang, D D Fan, P H Jiang, J Shi
Phosphorene has attracted tremendous interest recently due to its intriguing electronic properties. However, the thermal transport properties of phosphorene, especially for its allotropes, are still not well-understood. In this work, we calculate the thermal conductivities of five phosphorene allotropes (α-, β-, γ-, δ- and ζ-phase) by using phonon Boltzmann transport theory combined with first-principles calculations. It is found that the α-phosphorene exhibits considerable anisotropic thermal transport, while it is less obvious in the other four phosphorene allotropes...
July 4, 2017: Scientific Reports
Francesco Ricci, Wei Chen, Umut Aydemir, G Jeffrey Snyder, Gian-Marco Rignanese, Anubhav Jain, Geoffroy Hautier
Electronic transport in materials is governed by a series of tensorial properties such as conductivity, Seebeck coefficient, and effective mass. These quantities are paramount to the understanding of materials in many fields from thermoelectrics to electronics and photovoltaics. Transport properties can be calculated from a material's band structure using the Boltzmann transport theory framework. We present here the largest computational database of electronic transport properties based on a large set of 48,000 materials originating from the Materials Project database...
July 4, 2017: Scientific Data
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