Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519925
S. Johnsen, A. Bentien, G. Madsen, M. Nygren, B. Iversen
Calculated transport properties based on density functional theory calculations for Ba/sub 8/Cu/sub 6/Ge/sub 40/ predict the power function to be enhanced for a Fermi level located just below the top of the valence band. To explore the potential of Cu containing Ge clathrates as thermoelectric materials we have synthesized eight samples with nominal stoichiometry Ba/sub 8/Cu/sub 6-x/Ge/sub 40+x/ x = 0 - 0.7. This is an ongoing project and we present here some of our preliminary results for the x = 0.1 sample. Contradictory to expectation n-type behavior is observed in this sample. Furthermore, the thermoelectric properties are relatively poor, mainly due to the low mobility of the charge carriers that results in a high resistivity.
{"title":"Copper containing germanium clathrates","authors":"S. Johnsen, A. Bentien, G. Madsen, M. Nygren, B. Iversen","doi":"10.1109/ICT.2005.1519925","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519925","url":null,"abstract":"Calculated transport properties based on density functional theory calculations for Ba/sub 8/Cu/sub 6/Ge/sub 40/ predict the power function to be enhanced for a Fermi level located just below the top of the valence band. To explore the potential of Cu containing Ge clathrates as thermoelectric materials we have synthesized eight samples with nominal stoichiometry Ba/sub 8/Cu/sub 6-x/Ge/sub 40+x/ x = 0 - 0.7. This is an ongoing project and we present here some of our preliminary results for the x = 0.1 sample. Contradictory to expectation n-type behavior is observed in this sample. Furthermore, the thermoelectric properties are relatively poor, mainly due to the low mobility of the charge carriers that results in a high resistivity.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"56 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124046420","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519935
M. Smeller, Fred R. Harris, David C. Johnson
Reliable synthesis techniques are essential for industrial thermoelectric applications. The modulated elemental reactant (MER) method was used to make a set of seven (Bi/sub 2/Te/sub 3/)/sub 5/(TiTe/sub 2/)/sub 4/ superlattices, with a superlattice period reproducible to within 0.6%. The electrical properties of these samples were controlled by the distribution and densities of defects. Annealing at 270/spl deg/C changed the Seebeck coefficient from -60 /spl mu/V/K to -200 /spl mu/V/K after 111 hours annealing at 270/spl deg/C.
{"title":"Repeatable synthesis of (Bi/sub 2/Te/sub 3/)/sub 5/(TiTe/sub 2/)/sub 4/ superlattices using modulated elemental reactants","authors":"M. Smeller, Fred R. Harris, David C. Johnson","doi":"10.1109/ICT.2005.1519935","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519935","url":null,"abstract":"Reliable synthesis techniques are essential for industrial thermoelectric applications. The modulated elemental reactant (MER) method was used to make a set of seven (Bi/sub 2/Te/sub 3/)/sub 5/(TiTe/sub 2/)/sub 4/ superlattices, with a superlattice period reproducible to within 0.6%. The electrical properties of these samples were controlled by the distribution and densities of defects. Annealing at 270/spl deg/C changed the Seebeck coefficient from -60 /spl mu/V/K to -200 /spl mu/V/K after 111 hours annealing at 270/spl deg/C.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"57 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124446107","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519918
M. Itoh, H. Kitagawa, T. Kodama, H. Noguchi, S. Sota, K. Hasezaki, Y. Noda
Temperature dependence of the Seebeck coefficient of Bi-Sb alloy, which is known to be an efficient thermoelectric material, is investigated in terms of the multi-carrier Boltzmann transport theory. The chemical potential is calculated self-consistently with the measured Hall coefficient, by solving an integral equation. The calculated chemical potential shows a clear indication of the extrinsic-to-intrinsic transition, and determines the temperature dependence of all the transport properties. In particular, maximum thermopower is bound to occur in the vicinity of the transition temperature. It is confirmed that the electrons in the L-point conduction band act as dominant carriers, whereas the valence bands at the L, T and H points serve primarily as carrier reservoirs. The electrons are sufficiently degenerate that the conventional analysis is misleading, corresponding to the unphysical solution of the equation.
{"title":"Mechanism of thermopower maximum of Bi-Sb semiconducting alloys","authors":"M. Itoh, H. Kitagawa, T. Kodama, H. Noguchi, S. Sota, K. Hasezaki, Y. Noda","doi":"10.1109/ICT.2005.1519918","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519918","url":null,"abstract":"Temperature dependence of the Seebeck coefficient of Bi-Sb alloy, which is known to be an efficient thermoelectric material, is investigated in terms of the multi-carrier Boltzmann transport theory. The chemical potential is calculated self-consistently with the measured Hall coefficient, by solving an integral equation. The calculated chemical potential shows a clear indication of the extrinsic-to-intrinsic transition, and determines the temperature dependence of all the transport properties. In particular, maximum thermopower is bound to occur in the vicinity of the transition temperature. It is confirmed that the electrons in the L-point conduction band act as dominant carriers, whereas the valence bands at the L, T and H points serve primarily as carrier reservoirs. The electrons are sufficiently degenerate that the conventional analysis is misleading, corresponding to the unphysical solution of the equation.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"155 4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128694940","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519912
N. Sato, Masatoshi Takeda
The purpose of this work is to fabricate and evaluate a flexible thermoelectric (TE) device. Because of its flexibility, it is expected that application field of the TE device will be enlarged. The device consists of p and n-type thin films placed between 2 polyimide sheets, and it can generate electricity from temperature difference (/spl Delta/T/sub out/) applied between the outer surfaces of the device. The /spl Delta/T/sub out/ is transformed into in-plane temperature difference (/spl Delta/T/sub in/), which can be utilized for thermoelectric power generation by the p-n couple. The /spl Delta/T/sub in/ was measured as 16.7 K when /spl Delta/T/sub out/ was 57.8 K, being in good agreement with calculated value by Finite Element Method. Calculations revealed that the use of TE material with high power factor is effective, and low thermal conductivity will be not so important for this device performance. Chromel as p-type and constantan as n-type was, therefore, selected for the flexible TE device. The device composed of 9 pairs of the films was fabricated by RF-sputtering-method. The device could generate maximum output of 144 nW at /spl Delta/T/sub out/ = 28.6 K in measurement. According to the calculation, maximum out of 114 nW at /spl Delta/T/sub out/ = 28.6 K was predicted, being in good agreement with measured value.
{"title":"Fabrication and evaluation of a flexible thermoelectric device using metal thin films","authors":"N. Sato, Masatoshi Takeda","doi":"10.1109/ICT.2005.1519912","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519912","url":null,"abstract":"The purpose of this work is to fabricate and evaluate a flexible thermoelectric (TE) device. Because of its flexibility, it is expected that application field of the TE device will be enlarged. The device consists of p and n-type thin films placed between 2 polyimide sheets, and it can generate electricity from temperature difference (/spl Delta/T/sub out/) applied between the outer surfaces of the device. The /spl Delta/T/sub out/ is transformed into in-plane temperature difference (/spl Delta/T/sub in/), which can be utilized for thermoelectric power generation by the p-n couple. The /spl Delta/T/sub in/ was measured as 16.7 K when /spl Delta/T/sub out/ was 57.8 K, being in good agreement with calculated value by Finite Element Method. Calculations revealed that the use of TE material with high power factor is effective, and low thermal conductivity will be not so important for this device performance. Chromel as p-type and constantan as n-type was, therefore, selected for the flexible TE device. The device composed of 9 pairs of the films was fabricated by RF-sputtering-method. The device could generate maximum output of 144 nW at /spl Delta/T/sub out/ = 28.6 K in measurement. According to the calculation, maximum out of 114 nW at /spl Delta/T/sub out/ = 28.6 K was predicted, being in good agreement with measured value.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127493889","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519983
H. Kitagawa, M. Wakatsuki, Y. Isoda, Y. Shinohara, K. Hasezaki, Y. Noda
Co/sub 1-x/Ni/sub x/Sb/sub 3/ (x = 0.005/spl ap/0.1) samples were prepared by direct melting of constituent elements in a graphite crucible and subsequently was sintered using spark plasma sintering. The temperature dependence of the Hall coefficient, Hall mobility, Seebeck coefficient, electrical resistivity and thermal conductivity were investigated in a temperature range from 20 to 773 K. All the measured samples are n-type semiconductor and the conduction type changes from n- to p-type at around 450 K. The temperature for the transition from n-type to p-type increased with increasing Ni content x. The scattering factor, Fermi energy and Lorenz number were estimated and thermal conductivity was analyzed as a function of temperature. The lattice component of thermal conductivity is dominant at low temperatures but carrier and bipolar components become large at temperatures higher than the transition temperature.
{"title":"Analysis of thermal conductivity in Ni-doped CoSb/sub 3/","authors":"H. Kitagawa, M. Wakatsuki, Y. Isoda, Y. Shinohara, K. Hasezaki, Y. Noda","doi":"10.1109/ICT.2005.1519983","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519983","url":null,"abstract":"Co/sub 1-x/Ni/sub x/Sb/sub 3/ (x = 0.005/spl ap/0.1) samples were prepared by direct melting of constituent elements in a graphite crucible and subsequently was sintered using spark plasma sintering. The temperature dependence of the Hall coefficient, Hall mobility, Seebeck coefficient, electrical resistivity and thermal conductivity were investigated in a temperature range from 20 to 773 K. All the measured samples are n-type semiconductor and the conduction type changes from n- to p-type at around 450 K. The temperature for the transition from n-type to p-type increased with increasing Ni content x. The scattering factor, Fermi energy and Lorenz number were estimated and thermal conductivity was analyzed as a function of temperature. The lattice component of thermal conductivity is dominant at low temperatures but carrier and bipolar components become large at temperatures higher than the transition temperature.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130444656","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519928
J. Martín, S. Erickson, G. Nolas, P. Alboni, T. Tritt
We report the synthesis of the Si-Ge alloy type I clathrate Ba/sub 8/Ga/sub 16/Si/sub x/Ge/sub 30-x/ including a systematic investigation of the electrical properties by varying the Si-to-Ge ratio while a constant Ga-to-group IV element ratio is maintained. These Si-Ge type I clathrate samples demonstrate transport properties in direct contrast to those expected in a typical rigid band semiconducting material. The increasing Si substitution correlates to an increase in |S| even as the resistivity decreases and the carrier concentration increases, suggesting a modified band structure as compared to Ba/sub 8/Ga/sub 16/Ge/sub 30/. The structural, chemical, and electrical transport properties of Ba/sub 8/Ga/sub 16/Si/sub x/Ge/sub 30-x/ are reported in comparison to Ba/sub 8/Ga/sub 16/Ge/sub 30/ and Sr/sub 8/Ga/sub 16/Si/sub x/Ge/sub 30-x/.
{"title":"Thermoelectric properties of Ba-filled Si-Ge alloy type I semiconducting clathrates","authors":"J. Martín, S. Erickson, G. Nolas, P. Alboni, T. Tritt","doi":"10.1109/ICT.2005.1519928","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519928","url":null,"abstract":"We report the synthesis of the Si-Ge alloy type I clathrate Ba/sub 8/Ga/sub 16/Si/sub x/Ge/sub 30-x/ including a systematic investigation of the electrical properties by varying the Si-to-Ge ratio while a constant Ga-to-group IV element ratio is maintained. These Si-Ge type I clathrate samples demonstrate transport properties in direct contrast to those expected in a typical rigid band semiconducting material. The increasing Si substitution correlates to an increase in |S| even as the resistivity decreases and the carrier concentration increases, suggesting a modified band structure as compared to Ba/sub 8/Ga/sub 16/Ge/sub 30/. The structural, chemical, and electrical transport properties of Ba/sub 8/Ga/sub 16/Si/sub x/Ge/sub 30-x/ are reported in comparison to Ba/sub 8/Ga/sub 16/Ge/sub 30/ and Sr/sub 8/Ga/sub 16/Si/sub x/Ge/sub 30-x/.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121076537","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519939
P. Mayer, Rajeev J Ram
A thermoelectric power generator using thin-film materials presents many challenges due to its inherently large temperature gradient and correspondingly large power density. We present measurements of generated power density from BiTe-based thin-film and thick-film single-element devices (Marlow) in a variety of different element lengths (150-1500 micron) with an experimental setup capable of generating a large temperature difference (>300 K) across the films, and a novel load-matching scheme capable of matching milliohm impedances. Power densities in excess of 2 W/cm have been measured from a single element. The heat spreading in the copper contacts allows an effective heat transfer coefficient of h=18 W/cm/sup 2//K, and the parasitic electrical resistance of the system is below 12 m/spl Omega/. The same setup has also been used to obtain power measurements on thin-film superlattice thermoelectric elements. The effects of non-idealities such as imperfect impedance matching and non-zero thermal contact resistance are discussed in light of this data.
{"title":"Thin-film thermoelectric generator element characterization","authors":"P. Mayer, Rajeev J Ram","doi":"10.1109/ICT.2005.1519939","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519939","url":null,"abstract":"A thermoelectric power generator using thin-film materials presents many challenges due to its inherently large temperature gradient and correspondingly large power density. We present measurements of generated power density from BiTe-based thin-film and thick-film single-element devices (Marlow) in a variety of different element lengths (150-1500 micron) with an experimental setup capable of generating a large temperature difference (>300 K) across the films, and a novel load-matching scheme capable of matching milliohm impedances. Power densities in excess of 2 W/cm have been measured from a single element. The heat spreading in the copper contacts allows an effective heat transfer coefficient of h=18 W/cm/sup 2//K, and the parasitic electrical resistance of the system is below 12 m/spl Omega/. The same setup has also been used to obtain power measurements on thin-film superlattice thermoelectric elements. The effects of non-idealities such as imperfect impedance matching and non-zero thermal contact resistance are discussed in light of this data.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"83 3-4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116562256","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519954
R. Welle, B. Hardy
Valves for microfluidic systems have, for various reasons, proven to be difficult to fabricate, cumbersome to operate, and/or unreliable. We have explored the performance of a novel microfluidic valve formed by creating a flow channel past a Peltier junction. When the Peltier junction is used as a thermoelectric cooler it is possible to freeze the fluid in the valve, forming an ice plug that blocks flow through the valve. This type of valve is fundamentally leak-free, has no moving parts, and is electrically actuated. We have fabricated several experimental prototypes and evaluated their performance. We find that they are reliably capable of closing in less than 100 ms, and of opening substantially faster.
{"title":"Peltier-actuated microvalve performance optimization","authors":"R. Welle, B. Hardy","doi":"10.1109/ICT.2005.1519954","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519954","url":null,"abstract":"Valves for microfluidic systems have, for various reasons, proven to be difficult to fabricate, cumbersome to operate, and/or unreliable. We have explored the performance of a novel microfluidic valve formed by creating a flow channel past a Peltier junction. When the Peltier junction is used as a thermoelectric cooler it is possible to freeze the fluid in the valve, forming an ice plug that blocks flow through the valve. This type of valve is fundamentally leak-free, has no moving parts, and is electrically actuated. We have fabricated several experimental prototypes and evaluated their performance. We find that they are reliably capable of closing in less than 100 ms, and of opening substantially faster.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"310 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122425082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519999
Bing Shen, Robert Hendry, Jai Cancheevaram, C. Watkins, Mike Mantini, Rama Venkatasubramanian
With recent advancements in thermoelectric material performance, thermoelectric generators have become a viable alternative for power generation using small temperature differentials with benefits that can not be found in other energy conversion methods. The power generated by a thermoelectric generator, using a small /spl Delta/T, is characterized by a relatively high current (-/spl sim/5 A), but a relatively low voltage (<0.3 V), which is often not suited for many practical applications. In order to make use of the thermoelectric generated power in applications requiring a higher voltage, a DC-DC step up converter that can handle low input voltage is needed. Commercial available DC step up converters require an input voltage of at least 0.7 volts, which is the minimal voltage required for operating a bipolar junction switch. Several novel approaches for low input voltage DC-DC converter concepts have been studied and proved to be feasible. Their operations are based on some unconventional methods achieving DC to AC conversion for low input voltage. In one solid state approach, a normally-on transistor and a tunnel diode were utilized to achieve low voltage oscillation. A conversion concept was also developed which is based on an electromagnetic actuated mechanical switch. Operating principles and measured performance of these approaches will be reported.
{"title":"DC-DC converter suitable for thermoelectric generator","authors":"Bing Shen, Robert Hendry, Jai Cancheevaram, C. Watkins, Mike Mantini, Rama Venkatasubramanian","doi":"10.1109/ICT.2005.1519999","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519999","url":null,"abstract":"With recent advancements in thermoelectric material performance, thermoelectric generators have become a viable alternative for power generation using small temperature differentials with benefits that can not be found in other energy conversion methods. The power generated by a thermoelectric generator, using a small /spl Delta/T, is characterized by a relatively high current (-/spl sim/5 A), but a relatively low voltage (<0.3 V), which is often not suited for many practical applications. In order to make use of the thermoelectric generated power in applications requiring a higher voltage, a DC-DC step up converter that can handle low input voltage is needed. Commercial available DC step up converters require an input voltage of at least 0.7 volts, which is the minimal voltage required for operating a bipolar junction switch. Several novel approaches for low input voltage DC-DC converter concepts have been studied and proved to be feasible. Their operations are based on some unconventional methods achieving DC to AC conversion for low input voltage. In one solid state approach, a normally-on transistor and a tunnel diode were utilized to achieve low voltage oscillation. A conversion concept was also developed which is based on an electromagnetic actuated mechanical switch. Operating principles and measured performance of these approaches will be reported.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"40 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131178424","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2005-06-19DOI: 10.1109/ICT.2005.1519989
T. Takeuchi, T. Kitao, T. Kondo, M. Mikami
Angle resolved photoemission spectroscopy (ARPES) with synchrotron radiation as an incident photon source was performed on the two different layered cobalt oxides, Ca/sub 3/Co/sub 4/O/sub 9/ and Na/sub 0.6/CoO/sub 2/. The energy-momentum dispersion was clearly observed in ARPES spectra, indicating the presence of extended and coherent Bloch states, and consequently the Boltzmann-type electrical conduction. The electronic structure near the Fermi level (E/sub F/) in Ca/sub 3/Co/sub 4/O/sub 9/ was assigned not to be those from the Ca/sub 2/CoO/sub 3/ rock-salt layers but consisting of the a/sub 1g/ and e'/sub g/ bands from the CoO/sub 2/ layers in the same manner as in Na/sub 0.6/CoO/sub 2/. The topology of the measured band was essentially the same with the calculated ones, but the energy width of the bands was greatly reduced to less than 60% of the calculated ones in both compounds most likely due to strong electron-correlation. The bilayer-splitting of the a/sub 1g/ and e'/sub g/ bands was observed for Na/sub 0.6/CoO/sub 2/ in sharp contrast with its absence in Ca/sub 3/Co/sub 4/O/sub 9/. This difference is caused by the difference in nature of the interstitial layers; thin disordered Na layer in Na/sub 0.6/CoO/sub 2/ and thick insulating Ca/sub 2/CoO/sub 3/ rock-salt layer in Ca/sub 3/Co/sub 4/O/sub 9/. Making full use of the measured electronic structure, we succeeded in qualitatively accounting for mechanism of the coexistence of a metallic electrical conduction with a large thermoelectric power.
{"title":"Electronic structure and its contribution to the thermoelectric power of Ca/sub 3/Co/sub 4/O/sub 9/ and Na/sub x/CoO/sub 2/ layered cobalt oxides","authors":"T. Takeuchi, T. Kitao, T. Kondo, M. Mikami","doi":"10.1109/ICT.2005.1519989","DOIUrl":"https://doi.org/10.1109/ICT.2005.1519989","url":null,"abstract":"Angle resolved photoemission spectroscopy (ARPES) with synchrotron radiation as an incident photon source was performed on the two different layered cobalt oxides, Ca/sub 3/Co/sub 4/O/sub 9/ and Na/sub 0.6/CoO/sub 2/. The energy-momentum dispersion was clearly observed in ARPES spectra, indicating the presence of extended and coherent Bloch states, and consequently the Boltzmann-type electrical conduction. The electronic structure near the Fermi level (E/sub F/) in Ca/sub 3/Co/sub 4/O/sub 9/ was assigned not to be those from the Ca/sub 2/CoO/sub 3/ rock-salt layers but consisting of the a/sub 1g/ and e'/sub g/ bands from the CoO/sub 2/ layers in the same manner as in Na/sub 0.6/CoO/sub 2/. The topology of the measured band was essentially the same with the calculated ones, but the energy width of the bands was greatly reduced to less than 60% of the calculated ones in both compounds most likely due to strong electron-correlation. The bilayer-splitting of the a/sub 1g/ and e'/sub g/ bands was observed for Na/sub 0.6/CoO/sub 2/ in sharp contrast with its absence in Ca/sub 3/Co/sub 4/O/sub 9/. This difference is caused by the difference in nature of the interstitial layers; thin disordered Na layer in Na/sub 0.6/CoO/sub 2/ and thick insulating Ca/sub 2/CoO/sub 3/ rock-salt layer in Ca/sub 3/Co/sub 4/O/sub 9/. Making full use of the measured electronic structure, we succeeded in qualitatively accounting for mechanism of the coexistence of a metallic electrical conduction with a large thermoelectric power.","PeriodicalId":422400,"journal":{"name":"ICT 2005. 24th International Conference on Thermoelectrics, 2005.","volume":"113 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2005-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133625086","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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