+- Report on ICT2006

+- Report on ICT2006 +- Overview & Statistics +- Proceedings +- Awards: Best Paper, Goldsmid & Young Investigator +- Selected Highlights +- ICT2007 Sets Dates – June 3-7, 2007 +- Society Updates: ICT2008, Elections & Other News +- Overview & Statistics The 25th International Conference on Thermoelectrics was held August 6-10, 2006 in one of Europe’s finest cities, Vienna. For those with the interest and time Vienna offers Castles & Palaces, Museums, music and some excellent bratwurst and beer. The Natural History Museum alone was worth the trip and qualifies as a business expense if you examine the skutterudite, bismuth telluride and lead telluride specimens in their mineralogy collection. The social highlight had to be the Reception held at the City Hall, complete with music and dance. The final day of the conference coincided with the breaking of the ‘liquid explosives’ plot in the UK and the associated air travel disruption and confusion which followed. Not a few of us managed to travel through London’s Heathrow in the days following the conference, suffering some stress and delay but only that. +- Report on ICT2006 +- Overview & Statistics +- Proceedings +- Awards: Best Paper, Goldsmid & Young Investigator +- Selected Highlights +- ICT2007 Sets Dates – June 3-7, 2007 +- Society Updates: ICT2008, Elections & Other News +- Overview & Statistics The 25th International Conference on Thermoelectrics was held August 6-10, 2006 in one of Europe’s finest cities, Vienna. For those with the interest and time Vienna offers Castles & Palaces, Museums, music and some excellent bratwurst and beer. The Natural History Museum alone was worth the trip and qualifies as a business expense if you examine the skutterudite, bismuth telluride and lead telluride specimens in their mineralogy collection. The social highlight had to be the Reception held at the City Hall, complete with music and dance. The final day of the conference coincided with the breaking of the ‘liquid explosives’ plot in the UK and the associated air travel disruption and confusion which followed. Not a few of us managed to travel through London’s Heathrow in the days following the conference, suffering some stress and delay but only that. ICT2006 set a record with 307 attendees, edging out ICT1993 held in Yokohama, Japan with 302 official attendees. Thirty nations were represented with large contingents from Japan (103), USA (35), Germany (24), S. Korea (23), Russia (19), France (17) and Austria (16). About 185 manuscripts were received. All will be reviewed before appearing in the Proceedings, a process which is already nearly complete. ICT2006 Attendance: ICT2006 held August 6-10, 2006 in Vienna, Austria set a new record with 307 attendees.ICT2006 Attendance: ICT2006 held August 6-10, 2006 in Vienna, Austria set a new record with 307 attendees. +- Proceedings ICT2006 required manuscripts be submitted prior to the conference, a procedure new to the ICTs but one which greatly facilitates the review and distribution process. As a result the organizers were able to provide each attendee with a CD-ROM containing all available as-received manuscripts. It was only after the fact realized that this CD-ROM might have been more accurately labeled “Submitted Manuscripts”, rather than “Proceedings”. Attendees will be mailed a second CD-ROM with the official Proceedings containing the peer-reviewed manuscripts. Shipping is expected before the end of 2006. Note that ICT2006 attendees will not be receiving printed hardcopy of the Proceedings. If you wish to order a hardcopy of the Proceedings you will need to contact the publisher, IEEE, directly by September 30, 2006 using the order form available online at: http://www.its.org/node/4718. Only a limited number of hardcopies will be produced, so place your order now. +- Awards: Best Paper, Goldsmid & Young Investigator http://www.its.org/bestpapers Each year at the ICT, papers are considered for one of two Awards: the Best Scientific Paper Award and the Best Applications Paper Award. Awards are presented only if unusually noteworthy papers are identified. Some preference is given to young investigators. Presently, the award includes a certificate and a check for US$500. A list of past winners is now available online at: http://www.its.org/bestpapers. [Editors note: Please let me know if you see errors or omissions in the online list.] At ICT2006 Michael Marek Koza received the Best Scientific Paper Award for his paper on neutron scattering in nanocage compounds. The general idea that ‘cage’ compounds might have unusually low thermal conductivity values was first suggested by G.A. Slack about 15-20 years ago and played a strong role in his consideration of skutterudites and clathrates (among others) as potential thermoelectric materials. The idea is to find a crystal structure with a void more than large enough to contain a ‘guest’ atom, which may then ‘rattle’ around and (hopefully) scatter phonons and lower the lattice thermal conductivity. The neutron scattering study by Koga et al is an important direct, experimental study of the phonon dynamics of these ‘rattlers’. Title: Lattice dynamics of thermoelectric nanocage-based compounds studied by inelastic neutron scattering. Authors: Koza, M.M.; Viennois, R.; Mutka, H.; Girard, L.; Ravot, D.; Toulemonde, P.; Miguel, A.S., Proceedings of the 25th International Conference on Thermoelectrics:, ICT2006, IEEE, Vienna, Austria, p.TBD (2006) Abstract: During the past ten years, nanocage based compounds like skutterudite and clathrate have attracted scientific attention due to their particular thermoelectric properties. In these compounds, the low thermal conductivity is believed to be due to the scattering of the heat-carrying phonons by the localized modes due to the rattling motion of the intercalated guest atoms in the nanocages. Hence, the experimental study of the lattice dynamics of these compounds is very important for confirming this picture. We hope to have an electronic version of Koga’s paper posted on the ITS website soon. Each year ITS also sponsors a “Goldsmid Award for Excellence in Research in Thermoelectrics by a Graduate Student” (http://www.its.org/taxonomy/term/257) and in 2006 initiated a new Award “ITS Young Investigator Award for Excellence in Research in Thermoelectrics” (http://www.its.org/taxonomy/term/258 ). These Awards each carry a certificate, a cash prize and are to be presented at the annual ICT Banquet, if suitable candidates have been nominated. In 2006 both Awards went unfilled because there were no applicants. While a formal announcement for the 2007 Goldsmid and Young Investigator Awards will not be made for some months, if you or someone you know are interested in these awards you might begin putting together your application package now. +- Selected Highlights It is not possible even to listen to all the presentations, much less to do justice to a report on them all. The following highlights, therefore, reflect my own interests and biases and those selected papers which caught my attention for one reason or another. I sincerely apologize for all the undoubted omissions and errors. Papers are presented here in no particular order, except for the obvious bias for chronology. Also note that I refer to each paper by the presenting author’s name only. I’m fully aware that virtually all papers represent a team (sometimes quite a large one), so please insert ‘they’ for ‘(s)he’ and ‘et al’ wherever seems appropriate. The full program for ICT2006, including all the authors for each paper, is available online at: http://www.univie.ac.at/ICT06/ICT06_ScientProgram_2707_final.pdf. Goldsmid, U. of New South Wales, Sydney, Australia Bismuth – The thermoelectric material of the future? TE grade Bi2Te3 costs about US$200/kg, which is driving people to consider ways of using less material. But there are limits to reducing the amount of material required imposed by contact resistances. So it is reasonable to consider ways of using bismuth alone, which costs only about US$20/kg. The ZT of n-type bismuth is thought to be attractive (possibly up to ZT~4) if the holes can be suppressed in bulk-like materials. Logvinov, Instituto Politecnico National, Mexico Contribution of Professor Anatoly Samoilovich to the Development of Thermoelectricity Logvinov commemorates the 100th birthday of Prof. Samoilovich with a synopsis of his contributions to thermoelectricity. Less well known outside the Soviet Union, Samoilovich was quite influential within the Soviet Union. He was active in both Leningrad (now St. Petersburg) and Chernovtsy, Ukraine where he founded what is now the Institute of Thermoelectricity headed by Prof. Anatychuk. Primarily a theoretical physicist, and burdened by physical handicap, Semoilovich nevertheless made important theoretical contributions and left behind a legacy of students and institutions active to this day. Crane, BSST, Irwindale, CA USA Maximizing the Performance of a Thermoelectric Generator Crane describes a TE generator design suitable for both waste heat and primary power generation incorporating a number of novel features intended to reduce costs, accommodate thermal expansion differences, and different segment thickness. A “Y” shaped thermocouple design (as distinct from the traditional “pi” shape) reduces thermal expansion issues, eliminates the need for the n- and p- legs to be of equal length and allows for thermal isolation (so that each thermocouple need not have the same temperature profile as all the others). An additional concept utilizes liquid metal joints for the electrical contact between connectors and the TE elements, intended to relieve thermal stress. TE material requirements may be as little as 1/6th that required for conventional devices. Johnson, U. Oregon, Eugene, Oregon, USA Engineering Low Thermal Conductivity in Novel Thermoelectric Materials Johnson reports remarkably thermal conductivity values in “designer nanolaminates” (synthetic structures with nano-scale periodicity, but not necessarily with thermally equilibrated crystal structures). Johnson notes that improvements in ZT reported by Kanatzidis, Harman and Venkatasubramanian all appear to be due primarily to reductions in lattice thermal conductivity. So his group began looking at more complex structures to lower thermal conductivity even more than possible with only two components. Various chemistries based mostly on bismuth telluride, as well as systems based on tungsten diselenide, were prepared using a ‘modulated elemental reaction’ synthesis method where atomic layers are deposited on a substrate with a profile approximating the desired compound, followed by annealing at sufficiently low temperatures such that diffusion is still slow. Metastable structures, nanolaminates, with good periodicity can be prepared by this method. Perhaps the most notable result to date involves the tungsten diselenide – based nanolaminates where thermal conductivity values well below the classically estimated minimum lattice thermal conductivity have been repeatedly observed. Indeed, values just below the thermal conductivity of ‘still air’ appear to be reproducible. Measurements were performed by David Cahill (U. of Illinois) and speed of sound measurements indicate the sound velocity in the nanolaminates is much lower than expected based on the bulk materials. The low sound velocity values explain how it is possible to reach thermal conductivity below the classical minimum. For those fixated on ZT, the electrical resistivity was orders of magnitude too high and ZT is quite small. Caillat, JPL, Pasadena, CA USA Development of a New Generation of High-Temperature Thermoelectric Couples for Space Applications Caillat reported on developments at JPL for space power applications. Promising low thermal conductivity and high ZT (ZT~1 @ 1275 K, nearly twice the state of the art SiGe values) were reported on p-type Si-Ge nanocomposites, which may play a role in far term space applications. The ZT values Zintl phase materials, Yb_14MnSb_11, have been reproduced with 10 batches and ZTmax ~ 1.4 +- 0.1 at very high temperatures. Sublimation at 1275 K is presently about 2000x higher than desired and remains a serious concern for these materials. Bell, BSST, Irwindale, CA USA High Capacity Thermoelectric Temperature Control Systems Bell reports on efforts to develop TE technology suitable for larger-scale cooling, heating and temperature control applications. Using an advanced thermodynamic cycle, increased power density designs and reduced temperature losses at TE/electrode interfaces TE systems become competitive with traditional two phase systems for heating and cooling capacities from 50 to 3,500 watts and TE material costs can be reduced by a factor of about four. Advanced design tools have been developed which show good correlation with experimental results on the new designs. In time, these new designs are expected to find application in the automobile market. BSST reports placing their current designs in automobiles at the rate of 1 million units last year, 1.3 million this year and 1.7 million projected for next year. Gaydina, RIF Corporation, Voronezh, Russia Application of Low-Power Thermoelectric Generators Gaydina reports on efforts at RIF corporation to develop a commercially available thermoelectric generator. Their 60 W (electrical), 12 V ‘Termit’ unit weighs 20 kg and is expected to last 10 years. The units use a radial thermocouple design, which in their design reduces heat losses substantially. Gaydina reports producing 10 such units this year, with plans to produce 100 units next year and a 500 watt unit in about six months. Gross, Office of Naval Research, USA Converging Concepts in Nano-Structure-Enhanced Thermoelectric Performance for Power Generation Gross presented an overview of thermoelectric materials, devices and systems supported by the Office of Naval Research, DARPA and interrelated programs. With an emphasis on exploiting the possibilities of nanostructures, end applications include waste heat recovery, primary and auxiliary power and alternator replacement. Over 25 University, industry and government laboratories are presently supported. One overall target is greater than 25% system conversion efficiency and a challenge is to achieve 40-50% of Carnot. Among supported projects is the LAST work by Kanatzidis where nanostructures may have a role in the enhanced ZT. Other objectives include ZT=4 in the 300-900 K range, to design and build a 1 kWe device and to publish results in peer-reviewed journals. Among results presented was a figure attributed to Venkatasubramanian indicating a measured ZT of about 3 for some of his Bi2Te3-based superlattice materials. O’Dwyer, University of Wollongong, Wollongong, Australia Power generation with nanowire resonant tunneling thermoelectrics In this report Mark O’Dwyer combines aspects of the Hicks & Dresselhaus (1992) theoretical work on nanowires with ideas introduced by Humphrey to achieve reversible thermoelectric energy conversion to describe the detailed requirements for a InAs/InP nanowire heterostructure capable of achieving near Carnot electronic efficiencies. The central idea is a nanowire with a single, embedded quantum dot through which electrons only with the suitable, resonant energy may tunnel. A detailed theoretical analysis of the energy levels follows for a device which may be fabricated with available techniques. The described device is expected to be dominated by phonon heat flow, but it is thought to provide proof of principle that near Carnot efficiency can actually be achieved in the electronic system. [Note that Mark O’Dwyer, mo15@uow.edu.au, is nearing completion of his studies in Australia and, one expects, might entertain inquiries regarding future positions.] Fukushima, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan. Peltier effect in sub-micron-sized metallic junctions Fukushima reports on the Peltier effect in sub-micron sized metallic junctions, such as Co/Au and Cr/Au interfaces, show a Peltier effect larger than expected from bulk materials of the same elements. Plots of electrical resistance vs. current are used to demonstrate the cooling effect. Since the electrical resistance, R, of metals increases with temperature, measurement of R is a proxy for measuring temperature. A plot of R vs. I can be expected to be roughly parabolic in shape due to joule heating, and a shift in the minimum off of I=0 indicates Peltier cooling. Due to the small size of the junctions, the measured cooling power was large (~ 10E5 W/cm^2) as was the current density (~ 0E7 A/cm^2). Measured cooling power was on the order of 100 microwatts, which the authors suggest may be large enough to be useful for some microelectronic applications. Qiu, CANMET Energy Technology Centre-Ottawa Natural Resources Canada, Ottawa, Canada Integrated Thermoelectric Generator and Application to Self-Powered Heating Systems Qiu reports on development of a 550 W tin-telluride-based thermoelectric module incorporated into a gas-fired furnace. The self-generated electrical power provides increased reliability for home heat sources and any excess power can be used to charge batteries or supplement the household power requirements. The converter operates with between 630 oC and about 75 oC. Bierschenk, Marlow Industries, Dallas, TX Assessment of TEC Requirements for Thermoelectrically Enhanced Heat Sinks for CPU Cooling Applications Bierschenk’s report focuses on the lifetime and other requirements TE coolers must meet in order to service the PC cooling market. Thermal cycling is one key lifetime limiting factor for computer CPUs. Based on 2 thermal cycles per day (i.e. turning your computer on twice a day) one estimates about 5,000 thermal cycles for 7 year service life. But CPU heat production when running computing intensive software increases the number of thermal cycles up to several millions over the service life. Several types of TE coolers were life tested to determine the mean time to failure (MTTF) of production coolers under several test conditions. With delta T values (i.e. thermal cycle temperature change) of 15 oC the TECs survived 2,000,000 cycles with less than 2% change in resistance, and were estimated to last 81 million cycles before resistance changes became unacceptable (10%). The authors conclude that TECs are extremely reliable even under the heavy thermal stresses required by CPU applications. Bierschenk indicated the CPU industry cost target of US$0.10/watt of cooling will be tough to meet, but that for high end (i.e. gaming) applications TECs were more attractive. Fedorov, Ioffe Institute, St. Petersburg, Russia Some peculiarities of development of efficient thermoelectrics on the base of silicon compounds. Fedorov reports ZTmax > 1.1 for n-type Mg_2Si_0.4Sn_0.6 between about 650 and 750 K, depending on doping level. Seebeck, resistivity and thermal conductivity were measured simultaneously between 80 – 850 K and for a range of doping levels. Key to the high ZT value is the degeneracy of two different conduction bands which occurs at this particular composition and enhance the Seebeck coefficient, amounting to up to a 50% enhancement in ZT. Chaput, Laboratoire de Physique des Materiaux, UMR, Nancy France Calculation of transport properties for thermoelectric materials Chaput discusses efforts to calculate thermoelectric transport properties from first principles, using band structure calculations as an input. The anisotropic thermoelectric properties Zinc are calculated and good agreement with experiment is achieved even for this difficult test case. Witanachchi,U. of South Florida, Tampa, FL USA Synthesis and Characterization of Bulk and Thin Film Type I and Type II Clathrate Materials for Thermoelectric and Optoelectronic Applications. Witanachchi uses a pulsed laser ablation method to prepare polycrystalline thin films of the type I clathrate Ba_8Ge_16Ge_30. SEM, XRD and EDX confirmed the low defect density, crystallinity and composition. Electrical resistivity measurements between 50-300 K are believed to be the first reported on a thin film clathrate. Resistivity decreases from about 10 to 3.5 ohm-cm as temperature increases from 50 to 300 K, indicating semiconducting behavior. The paper establishes a new fabrication technique suitable for studying the properties of clathrates. Welle, Aerospace Corporation, USA Stand-Off Pressures in the Peltier-Actuated Microvalve Welle describes use of a Peltier device to freeze the fluid in a flow channel suitable for micro-fluidic applications, thereby controlling the flow without need for the usual mechanical plunger actuated values. The present study focuses on determining the maximum stand-off pressure possible for such values and also studies the effects of supercooling. The valves are shown to withstand more than 10 MPa, exceeding Welle’s present ability to measure the pressure. Thermoelectric leg lengths were reduced to 300 microns to reduce response time to about 50 ms. Supercooling of the water working fluid becomes an issue in microfluidic devices, which are relatively free of nucleation sites. Experiments and thermal modeling indicate that supercooling of 15-20 oC can be expected in Peltier-actuated microvalves using water but such cooling can still be achieved and with satisfactory performance. Mori, National Institute for Materials Science, Tsukuba, Japan Homologous rare earth boron cluster compounds; a possible n-type counterpart to boron carbide Mori reports studies of boron-rich rare-earth compounds based on B_12 icosohedra (RE-B_x-C[N}) which exhibit both n-type and p-type behavior with low thermal conductivity (~ 0.02 W/cm-K), reasonably large Seebeck coefficient values (up to about +70 to -60 microV/K) and electrical resistivity values in the milliohm-cm range all at high temperatures (1000 K). Boron carbide and related boron cluster compounds have been of interest as potential high temperature TE materials for some years, but satisfactory n-type materials have been particularly difficult to find. These new compounds exhibit n-type behavior without extreme doping efforts. The conduction mechanism appears to be different from the variable-range hopping behavior typical of boron-carbide class materials. While the power factor values are presently not as high as desired, further development may yield materials useful as high as 1500 K. +- ICT2007 Sets Dates – June 3-7, 2007 Last year the Board selected Dr. H. W. Lee’s proposal from the Korea Electrotechnology Research Institute to host ICT2007 on Jeju Island, S. Korea. The dates for this conference have now been fixed at June 3-7, 2007. Further details will be provided by this mail list as they become available and we will keep the latest available information online at http://www.its.org/ict2007. +- Society Updates: ICT2007, ICT2008, Elections & Other News The Annual Board Meeting for the International Thermoelectric Society is held each year the day before the ICT proper opens. At ICT2006, as in some recent years, ITS business items required more discussion than convenient for a single session and a second meeting was held during the week. Some of the main items of discussion always include site selection for future ICTs, financial matters, elections and many other items. This year, in spite of a Call for Proposals, no formal proposals were received to host ICT2008. As a result, President Uher announced that the ITS Board would entertain proposals from attendees to host ICT2008 anywhere in the world. At this time the ITS Board has received several expressions of interest and has established a timetable to allow a site selection announcement by the end of 2006. For those looking ahead, the usual ITS rotation of locations would return the ICT to Europe in 2009. A formal Call for Proposals to host ICT2009 will eventually be issued, but potential host organizations should begin thinking about the matter now. There are typically about 12-14 members of the ITS Board, with staggered terms of 3 years. Voting by ICT attendees each year fills any vacancies, with the hope that Board membership will be geographically diverse. The three ITS Officers (currently President Uher, Treasurer Boettner, and Secretary Rowe) by the Board members from among the Board members. Also, each ICT chair automatically becomes a Board member in recognition of their key role in the Society. The terms of four ITS Board members expired at the end of ICT2006: Fleurial (JPL, USA) Koumoto (Nagoya, Japan) Rowe (Cardiff, Wales) and Tedenac (Nancy, France). Prof. Rowe was re-elected by the Board as ITS Secretary and therefore remains on the Board. Prof. Koumoto was re-elected to the Board by the attendees and therefore also remains on the Board. The terms of Dr. Fleurial and Prof. Tedenac have expired and they were not re-elected. Speaking as an ITS member and Webmaster I’d like to thank Jean-Pierre and Jean Claude for their service to the ITS. The sole addition to the ITS Board this year is Thierry Caillat (JPL, USA). Dr. Caillat is well known to the community and has served previously on the ITS Board. Welcome back Thierry! Finally, the ITS Board voted to add a Best Poster Award beginning with ICT2007 which will be in addition to the annual Best Scientific Paper and Best Applications Paper awards.