ALBERT

Description: Thermoelectric energy harvesting-the transformation of waste heat into useful electricity-is of great interest for energy sustainability. The main obstacle is the low thermoelectric efficiency of materials for converting heat to electricity, quantified by the thermoelectric figure of merit, ZT. The best available n-type materials for use in mid-temperature (500-900 K) thermoelectric generators have a relatively low ZT of 1 or less, and so there is much interest in finding avenues for increasing this figure of merit. Here we report a binary crystalline n-type material, In(4)Se(3-delta), which achieves the ZT value of 1.48 at 705 K-very high for a bulk material. Using high-resolution transmission electron microscopy, electron diffraction, and first-principles calculations, we demonstrate that this material supports a charge density wave instability which is responsible for the large anisotropy observed in the electric and thermal transport. The high ZT value is the result of the high Seebeck coefficient and the low thermal conductivity in the plane of the charge density wave. Our results suggest a new direction in the search for high-performance thermoelectric materials, exploiting intrinsic nanostructural bulk properties induced by charge density waves.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Rhyee, Jong-Soo -- Lee, Kyu Hyoung -- Lee, Sang Mock -- Cho, Eunseog -- Kim, Sang Il -- Lee, Eunsung -- Kwon, Yong Seung -- Shim, Ji Hoon -- Kotliar, Gabriel -- England -- Nature. 2009 Jun 18;459(7249):965-8. doi: 10.1038/nature08088.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Materials Research Laboratory, Samsung Advanced Institute of Technology, Yongin 446-712, Korea.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19536260" target="_blank"〉PubMed〈/a〉

Description: The widespread use of thermoelectric technology is constrained by a relatively low conversion efficiency of the bulk alloys, which is evaluated in terms of a dimensionless figure of merit (zT). The zT of bulk alloys can be improved by reducing lattice thermal conductivity through grain boundary and point-defect scattering, which target low- and high-frequency phonons. Dense dislocation arrays formed at low-energy grain boundaries by liquid-phase compaction in Bi(0.5)Sb(1.5)Te3 (bismuth antimony telluride) effectively scatter midfrequency phonons, leading to a substantially lower lattice thermal conductivity. Full-spectrum phonon scattering with minimal charge-carrier scattering dramatically improved the zT to 1.86 +/- 0.15 at 320 kelvin (K). Further, a thermoelectric cooler confirmed the performance with a maximum temperature difference of 81 K, which is much higher than current commercial Peltier cooling devices.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kim, Sang Il -- Lee, Kyu Hyoung -- Mun, Hyeon A -- Kim, Hyun Sik -- Hwang, Sung Woo -- Roh, Jong Wook -- Yang, Dae Jin -- Shin, Weon Ho -- Li, Xiang Shu -- Lee, Young Hee -- Snyder, G Jeffrey -- Kim, Sung Wng -- New York, N.Y. -- Science. 2015 Apr 3;348(6230):109-14. doi: 10.1126/science.aaa4166.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Materials Research Center, Samsung Advanced Institute of Technology, Samsung Electronics, Suwon 443-803, South Korea. sang.il.kim@samsung.com kimsungwng@skku.edu. ; Department of Nano Applied Engineering, Kangwon National University, Chuncheon 200-701, South Korea. ; Department of Energy Science, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon 440-746, South Korea. IBS Center for Integrated Nanostructure Physics, Institute for Basic Science, Sungkyunkwan University, Suwon 440-746, South Korea. ; Materials Research Center, Samsung Advanced Institute of Technology, Samsung Electronics, Suwon 443-803, South Korea. Materials Science, California Institute of Technology, Pasadena, California 91125, USA. ; Materials Research Center, Samsung Advanced Institute of Technology, Samsung Electronics, Suwon 443-803, South Korea. ; Department of Energy Science, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon 440-746, South Korea. Materials Science, California Institute of Technology, Pasadena, California 91125, USA. ; Department of Energy Science, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon 440-746, South Korea. IBS Center for Integrated Nanostructure Physics, Institute for Basic Science, Sungkyunkwan University, Suwon 440-746, South Korea. sang.il.kim@samsung.com kimsungwng@skku.edu.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25838382" target="_blank"〉PubMed〈/a〉

Description: We examine magnetic and electric field perturbations associated with a sudden commencement (SC), caused by an interplanetary (IP) shock passing over the Earth's magnetosphere on 16 February 2013. The SC was identified in the magnetic and electric field data measured at THEMIS-E (THE-E: MLT = 12.4, L = 6.3), Van Allen Probe-A (VAP-A: MLT = 3.2, L = 5.1), and Van Allen Probe-B (VAP-B: MLT = 0.2. L = 4.9) in the magnetosphere. During the SC interval, THE-E observed a dawnward-then-duskward electric (E) field perturbation around noon, while VAP-B observed a duskward E-field perturbation around midnight. VAP-A observed a dawnward-then-duskward E-field perturbation in the postmidnight sector, but the duration and magnitude of the dawnward E-perturbation are much shorter and weaker than that at THE-E. That is, the E-field signature changes with local time during the SC interval. The SuperDARN radar data indicate that the ionospheric plasma motions during the SC are mainly due to the E-field variations observed in space. This indicates that the SC-associated E-field in space plays a significant role in determining the dynamic variations of the ionospheric convection flow. By comparing previous SC MHD simulations and our observations, we suggest that the E-field variations observed at the spacecraft are produced by magnetospheric convection flows due to deformation of the magnetosphere as the IP shock sweeps the magnetopause.