The Experts below are selected from a list of 41505 Experts worldwide ranked by ideXlab platform
Mercouri G Kanatzidis - One of the best experts on this subject based on the ideXlab platform.
-
Ultralow thermal conductivity and high thermoelectric Figure of Merit in SnSe crystals
Nature, 2014Co-Authors: Li-dong Zhao, Gangjian Tan, Shih Han Lo, Chris Wolverton, Vinayak P. Dravid, Yongsheng Zhang, Ctirad Uher, Hui Sun, Mercouri G KanatzidisAbstract:The thermoelectric effect enables direct and reversible conversion between thermal and electrical energy, and provides a viable route for power generation from waste heat. The efficiency of thermoelectric materials is dictated by the dimensionless Figure of Merit, ZT (where Z is the Figure of Merit and T is absolute temperature), which governs the Carnot efficiency for heat conversion. Enhancements above the generally high threshold value of 2.5 have important implications for commercial deployment, especially for compounds free of Pb and Te. Here we report an unprecedented ZT of 2.6 ± 0.3 at 923 K, realized in SnSe single crystals measured along the b axis of the room-temperature orthorhombic unit cell. This material also shows a high ZT of 2.3 ± 0.3 along the c axis but a significantly reduced ZT of 0.8 ± 0.2 along the a axis. We attribute the remarkably high ZT along the b axis to the intrinsically ultralow lattice thermal conductivity in SnSe. The layered structure of SnSe derives from a distorted rock-salt structure, and features anomalously high Grüneisen parameters, which reflect the anharmonic and anisotropic bonding. We attribute the exceptionally low lattice thermal conductivity (0.23 ± 0.03 W m(-1) K(-1) at 973 K) in SnSe to the anharmonicity. These findings highlight alternative strategies to nanostructuring for achieving high thermoelectric performance.
-
lead free thermoelectrics high Figure of Merit in p type agsnmsbtem 2
Advanced Energy Materials, 2012Co-Authors: Mi Kyung Han, John Androulakis, Sungjin Kim, Mercouri G KanatzidisAbstract:Thermoelectric materials based on Pb-free compositions are of considerable current interest in environmentally friendly power-generation applications derived from waste-heat sources. Here, a new study of the thermoelectric properties of the tin-based compositions with the general formula AgSnmSbTem+2 (m = 2, 4, 5, 7, 10, 14, 18) is presented, where the m value is used as the tuning parameter of the thermoelectric properties. The electrical conductivity, Seebeck coefficient, and thermal conductivity are measured from 300 K to 723 K and the resulting thermoelectric Figure of Merit is determined as a function of the SnTe/AgSbTe2 ratio. A thermoelectric Figure of Merit ZT ≈1 is obtained at 710 K for m = 4, indicating that the system AgSnmSbTem+2 holds great promise as an alternative p-type, lead-free, thermoelectric material.
-
lead free thermoelectrics high Figure of Merit in p type agsn msbte m 2
Advanced Energy Materials, 2012Co-Authors: Mi Kyung Han, John Androulakis, Sungjin Kim, Mercouri G KanatzidisAbstract:Thermoelectric materials based on Pb-free compositions are of considerable current interest in environmentally friendly power-generation applications derived from waste-heat sources. Here, a new study of the thermoelectric properties of the tin-based compositions with the general formula AgSnmSbTem+2 (m = 2, 4, 5, 7, 10, 14, 18) is presented, where the m value is used as the tuning parameter of the thermoelectric properties. The electrical conductivity, Seebeck coefficient, and thermal conductivity are measured from 300 K to 723 K and the resulting thermoelectric Figure of Merit is determined as a function of the SnTe/AgSbTe2 ratio. A thermoelectric Figure of Merit ZT ≈1 is obtained at 710 K for m = 4, indicating that the system AgSnmSbTem+2 holds great promise as an alternative p-type, lead-free, thermoelectric material.
-
strained endotaxial nanostructures with high thermoelectric Figure of Merit
Nature Chemistry, 2011Co-Authors: Kanishka Biswas, Vinayak P. Dravid, Ctirad Uher, Mercouri G Kanatzidis, Qichun Zhang, Guoyu WangAbstract:Thermoelectric materials can directly generate electrical power from waste heat but the challenge is in designing efficient, stable and inexpensive systems. Nanostructuring in bulk materials dramatically reduces the thermal conductivity but simultaneously increases the charge carrier scattering, which has a detrimental effect on the carrier mobility. We have experimentally achieved concurrent phonon blocking and charge transmitting via the endotaxial placement of nanocrystals in a thermoelectric material host. Endotaxially arranged SrTe nanocrystals at concentrations as low as 2% were incorporated in a PbTe matrix doped with Na(2)Te. This effectively inhibits the heat flow in the system but does not affect the hole mobility, allowing a large power factor to be achieved. The crystallographic alignment of SrTe and PbTe lattices decouples phonon and electron transport and this allows the system to reach a thermoelectric Figure of Merit of 1.7 at ~800 K.
-
analysis of nanostructuring in high Figure of Merit ag1 xpbmsbte2 m thermoelectric materials
Advanced Functional Materials, 2009Co-Authors: B A Cook, Mercouri G Kanatzidis, Mi Kyung Han, M J Kramer, J L Harringa, Duck Young ChungAbstract:Thermoelectric materials based on quaternary compounds Ag1−xPbmSbTe2+m exhibit high dimensionless Figure-of-Merit values, ranging from 1.5 to 1.7 at 700 K. The primary factor contributing to the high Figure of Merit is a low lattice thermal conductivity, achieved through nanostructuring during melt solidification. As a consequence of nucleation and growth of a second phase, coherent nanoscale inclusions form throughout the material, which are believed to result in scattering of acoustic phonons while causing only minimal scattering of charge carriers. Here, characterization of the nanosized inclusions in Ag0.53Pb18Sb1.2Te20 that shows a strong tendency for crystallographic orientation along the {001} planes, with a high degree of lattice strain at the interface, consistent with a coherent interfacial boundary is reported. The inclusions are enriched in Ag relative to the matrix, and seem to adopt a cubic, 96 atom per unit cell Ag2Te phase based on the Ti2Ni type structure. In-situ high-temperature synchrotron radiation diffraction studies indicated that the inclusions remain thermally stable to at least 800 K.
Gang Chen - One of the best experts on this subject based on the ideXlab platform.
-
relationship between thermoelectric Figure of Merit and energy conversion efficiency
Proceedings of the National Academy of Sciences of the United States of America, 2015Co-Authors: Hee Seok Kim, Gang Chen, Weishu Liu, C W Chu, Zhifeng RenAbstract:The formula for maximum efficiency (ηmax) of heat conversion into electricity by a thermoelectric device in terms of the dimensionless Figure of Merit (ZT) has been widely used to assess the desirability of thermoelectric materials for devices. Unfortunately, the ηmax values vary greatly depending on how the average ZT values are used, raising questions about the applicability of ZT in the case of a large temperature difference between the hot and cold sides due to the neglect of the temperature dependences of the material properties that affect ZT. To avoid the complex numerical simulation that gives accurate efficiency, we have defined an engineering dimensionless Figure of Merit (ZT)eng and an engineering power factor (PF)eng as functions of the temperature difference between the cold and hot sides to predict reliably and accurately the practical conversion efficiency and output power, respectively, overcoming the reporting of unrealistic efficiency using average ZT values.
-
enhancement of thermoelectric Figure of Merit by resonant states of aluminium doping in lead selenide
Energy and Environmental Science, 2012Co-Authors: Weishu Liu, Qinyong Zhang, Haiyan Wang, Hengzhi Wang, Qian Zhang, Zhiting Tian, Sangyeop Lee, Keivan Esfarjani, Gang ChenAbstract:By adding aluminium (Al) into lead selenide (PbSe), we successfully prepared n-type PbSe thermoelectric materials with a Figure-of-Merit (ZT) of 1.3 at 850 K. Such a high ZT is achieved by a combination of high Seebeck coefficient caused by very possibly the resonant states in the conduction band created by Al dopant and low thermal conductivity from nanosized phonon scattering centers.
-
enhanced thermoelectric Figure of Merit of p type half heuslers
Nano Letters, 2011Co-Authors: Xiao Yan, Giri Joshi, Yucheng Lan, Terry M Tritt, Weishu Liu, Sangyeop Lee, Hui Wang, J W Simonson, S J Poon, Gang ChenAbstract:Half-Heuslers would be important thermoelectric materials due to their high temperature stability and abundance if their dimensionless thermoelectric Figure of Merit (ZT) could be made high enough. The highest peak ZT of a p-type half-Heusler has been so far reported about 0.5 due to the high thermal conductivity. Through a nanocomposite approach using ball milling and hot pressing, we have achieved a peak ZT of 0.8 at 700 °C, which is about 60% higher than the best reported 0.5 and might be good enough for consideration for waste heat recovery in car exhaust systems. The improvement comes from a simultaneous increase in Seebeck coefficient and a significant decrease in thermal conductivity due to nanostructures. The samples were made by first forming alloyed ingots using arc melting and then creating nanopowders by ball milling the ingots and finally obtaining dense bulk by hot pressing. Further improvement in ZT is expected when average grain sizes are made smaller than 100 nm.
-
Enhancement of thermoelectric Figure-of-Merit by a bulk nanostructuring approach
Advanced Functional Materials, 2010Co-Authors: Yucheng Lan, Austin Jerome Minnich, Gang Chen, Zhifeng RenAbstract:Recently a significant Figure-of-Merit (ZT) improvement in the most-studied existing thermoelectric materials has been achieved by creating nanograins and nanostructures in the grains using the combination of high-energy ball milling and a direct-current-induced hot-press process. Thermoelectric transport measurements, coupled with microstructure studies and theoretical modeling, show that the ZT improvement is the result of low lattice thermal conductivity due to the increased phonon scattering by grain boundaries and structural defects. In this article, the synthesis process and the relationship between the microstructures and the thermoelectric properties of the nanostructured thermoelectric bulk materials with an enhanced ZT value are reviewed. It is expected that the nanostructured materials described here will be useful for a variety of applications such as waste heat recovery, solar energy conversion, and environmentally friendly refrigeration.
-
enhanced thermoelectric Figure of Merit in nanostructured n type silicon germanium bulk alloy
Applied Physics Letters, 2008Co-Authors: Xiaowei Wang, Giri Joshi, Andrew Muto, J Klatsky, S Song, Mildred S. Dresselhaus, Dezhi Wang, Jian Yang, Gang ChenAbstract:The dimensionless thermoelectric Figure of Merit (ZT) of the n-type silicon germanium (SiGe) bulk alloy at high temperature has remained at about one for a few decades. Here we report that by using a nanostructure approach, a peak ZT of about 1.3 at 900 °C in an n-type nanostructured SiGe bulk alloy has been achieved. The enhancement of ZT comes mainly from a significant reduction in the thermal conductivity caused by the enhanced phonon scattering off the increased density of nanograin boundaries. The enhanced ZT will make such materials attractive in many applications such as solar, thermal, and waste heat conversion into electricity.
Mildred S. Dresselhaus - One of the best experts on this subject based on the ideXlab platform.
-
enhanced thermoelectric Figure of Merit in nanostructured n type silicon germanium bulk alloy
Applied Physics Letters, 2008Co-Authors: Xiaowei Wang, Giri Joshi, Andrew Muto, J Klatsky, S Song, Mildred S. Dresselhaus, Dezhi Wang, Jian Yang, Gang ChenAbstract:The dimensionless thermoelectric Figure of Merit (ZT) of the n-type silicon germanium (SiGe) bulk alloy at high temperature has remained at about one for a few decades. Here we report that by using a nanostructure approach, a peak ZT of about 1.3 at 900 °C in an n-type nanostructured SiGe bulk alloy has been achieved. The enhancement of ZT comes mainly from a significant reduction in the thermal conductivity caused by the enhanced phonon scattering off the increased density of nanograin boundaries. The enhanced ZT will make such materials attractive in many applications such as solar, thermal, and waste heat conversion into electricity.
-
enhanced thermoelectric Figure of Merit in nanostructured p type silicon germanium bulk alloys
Nano Letters, 2008Co-Authors: Giri Joshi, Xiaowei Wang, Yucheng Lan, Dezhi Wang, Hohyun Lee, Gaohua Zhu, Ryan W Gould, Diana C Cuff, Ming Y Tang, Mildred S. DresselhausAbstract:A dimensionless thermoelectric Figure-of-Merit (ZT) of 0.95 in p-type nanostructured bulk silicon germanium (SiGe) alloys is achieved, which is about 90% higher than what is currently used in space flight missions, and 50% higher than the reported record in p-type SiGe alloys. These nanostructured bulk materials were made by using a direct current-induced hot press of mechanically alloyed nanopowders that were initially synthesized by ball milling of commercial grade Si and Ge chunks with boron powder. The enhancement of ZT is due to a large reduction of thermal conductivity caused by the increased phonon scattering at the grain boundaries of the nanostructures combined with an increased power factor at high temperatures.
-
thermoelectric Figure of Merit of a one dimensional conductor
Physical Review B, 1993Co-Authors: L. D. Hicks, Mildred S. DresselhausAbstract:We investigate the effect on the thermoelectric Figure of Merit of preparing materials in the form of one-dimensional conductors or quantum wires. Our calculations show that this approach has the potential to achieve a significant increase in the Figure of Merit over both the bulk value and the calculated superlattice values.
-
Effect of quantum-well structures on the thermoelectric Figure of Merit
Physical Review B, 1993Co-Authors: L. D. Hicks, Mildred S. DresselhausAbstract:Currently the materials with the highest thermoelectric Figure of Merit Z are BizTe3 alloys. There- fore these compounds are the best thermoelectric refrigeration elements. However, since the 1960s only slow progress has been made in enhancing Z, either in Bi2Te3 alloys or in other thermoelectric materials. So far, the materials used in applications have all been in bulk form. In this paper, it is proposed that it may be possible to increase Z of certain materials by preparing them in quantum- well superlattice structures. Calculations have been done to investigate the potential for such an approach, and also to evaluate the efFect of anisotropy on the Figure of Merit. The calculations show that layering has the potential to increase significantly the Figure of Merit of a highly anisotropic material such as BizTe3, provided that the superlattice multilayers are made in a particular orienta- tion. This result opens the possibility of using quantum-well superlattice structures to enhance the performance of thermoelectric coolers.
Giri Joshi - One of the best experts on this subject based on the ideXlab platform.
-
enhanced thermoelectric Figure of Merit of p type half heuslers
Nano Letters, 2011Co-Authors: Xiao Yan, Giri Joshi, Yucheng Lan, Terry M Tritt, Weishu Liu, Sangyeop Lee, Hui Wang, J W Simonson, S J Poon, Gang ChenAbstract:Half-Heuslers would be important thermoelectric materials due to their high temperature stability and abundance if their dimensionless thermoelectric Figure of Merit (ZT) could be made high enough. The highest peak ZT of a p-type half-Heusler has been so far reported about 0.5 due to the high thermal conductivity. Through a nanocomposite approach using ball milling and hot pressing, we have achieved a peak ZT of 0.8 at 700 °C, which is about 60% higher than the best reported 0.5 and might be good enough for consideration for waste heat recovery in car exhaust systems. The improvement comes from a simultaneous increase in Seebeck coefficient and a significant decrease in thermal conductivity due to nanostructures. The samples were made by first forming alloyed ingots using arc melting and then creating nanopowders by ball milling the ingots and finally obtaining dense bulk by hot pressing. Further improvement in ZT is expected when average grain sizes are made smaller than 100 nm.
-
enhanced thermoelectric Figure of Merit in nanostructured n type silicon germanium bulk alloy
Applied Physics Letters, 2008Co-Authors: Xiaowei Wang, Giri Joshi, Andrew Muto, J Klatsky, S Song, Mildred S. Dresselhaus, Dezhi Wang, Jian Yang, Gang ChenAbstract:The dimensionless thermoelectric Figure of Merit (ZT) of the n-type silicon germanium (SiGe) bulk alloy at high temperature has remained at about one for a few decades. Here we report that by using a nanostructure approach, a peak ZT of about 1.3 at 900 °C in an n-type nanostructured SiGe bulk alloy has been achieved. The enhancement of ZT comes mainly from a significant reduction in the thermal conductivity caused by the enhanced phonon scattering off the increased density of nanograin boundaries. The enhanced ZT will make such materials attractive in many applications such as solar, thermal, and waste heat conversion into electricity.
-
enhanced thermoelectric Figure of Merit in nanostructured p type silicon germanium bulk alloys
Nano Letters, 2008Co-Authors: Giri Joshi, Xiaowei Wang, Yucheng Lan, Dezhi Wang, Hohyun Lee, Gaohua Zhu, Ryan W Gould, Diana C Cuff, Ming Y Tang, Mildred S. DresselhausAbstract:A dimensionless thermoelectric Figure-of-Merit (ZT) of 0.95 in p-type nanostructured bulk silicon germanium (SiGe) alloys is achieved, which is about 90% higher than what is currently used in space flight missions, and 50% higher than the reported record in p-type SiGe alloys. These nanostructured bulk materials were made by using a direct current-induced hot press of mechanically alloyed nanopowders that were initially synthesized by ball milling of commercial grade Si and Ge chunks with boron powder. The enhancement of ZT is due to a large reduction of thermal conductivity caused by the increased phonon scattering at the grain boundaries of the nanostructures combined with an increased power factor at high temperatures.
Tie-jun Zhu - One of the best experts on this subject based on the ideXlab platform.
-
unique role of refractory ta alloying in enhancing the Figure of Merit of nbfesb thermoelectric materials
Advanced Energy Materials, 2018Co-Authors: Yintu Liu, Xin Bing Zhao, Umut Aydemir, Jeffrey G Snyder, Kaiyang Xia, Thomas C Chasapis, Tie-jun ZhuAbstract:NbFeSb-based half-Heusler alloys have been recently identified as promising high-temperature thermoelectric materials with a Figure of Merit zT > 1, but their thermal conductivity is still relatively high. Alloying Ta at the Nb site would be highly desirable because the large mass fluctuation between them could effectively scatter phonons and reduce the lattice thermal conductivity. However, practically it is a great challenge due to the high melting point of refractory Ta. Here, the successful synthesis of Ta-alloyed (Nb1−xTax)0.8Ti0.2FeSb (x = 0 – 0.4) solid solutions with significantly reduced thermal conductivity by levitation melting is reported. Because of the similar atomic sizes and chemistry of Nb and Ta, the solid solutions exhibit almost unaltered electrical properties. As a result, an overall zT enhancement from 300 to 1200 K is realized in the single-phase Ta-alloyed solid solutions, and the compounds with x = 0.36 and 0.4 reach a maximum zT of 1.6 at 1200 K. This work also highlights that the isoelectronic substitution by atoms with similar size and chemical nature but large mass difference should reduce the lattice thermal conductivity but maintain good electrical properties in thermoelectric materials, which can be a guide for optimizing the Figure of Merit by alloying.
-
realizing high Figure of Merit in heavy band p type half heusler thermoelectric materials
Nature Communications, 2015Co-Authors: Shengqiang Bai, Xin Bing Zhao, Yintu Liu, Lidong Chen, Yunshan Tang, Tie-jun ZhuAbstract:Thermoelectric materials could be used to convert waste heat into useful electricity, but the ideal substance needs to both optimize the electrical power factor and suppress thermal conductivity. Here, the authors report a high Figure of Merit of 1.5 at 1,200 K in the p-type half-Heusler alloy FeNbSb.