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Antoine Maignan - One of the best experts on this subject based on the ideXlab platform.
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Thermoelectric properties in the misfit-layered-Cobalt Oxides [Bi2A2O4][CoO2]b1/b2 (A=Ca, Sr, Ba, b1/b2=1.65, 1.82, 1.98) single crystals
2007 26th International Conference on Thermoelectrics, 2007Co-Authors: W. Kobayashi, Denis Pelloquin, S. Hébert, D Grebille, H. Muguerra, Antoine MaignanAbstract:Single crystals of different phases of misfit Cobalt Oxides have been synthesized. Using these materials, the intrinsic power factor has been determined. By combining thermopower S and Hall coefficient measurements, we will show how S can be tuned by doping in this family of materials, the doping being strongly dependent on the misfit ratio p=b1/b2 ([Bi2A2O4][CoO2]b1/b2 with A=Ca, Sr, Ba, b1/b2=1.65, 1.82, 1.98). The in-plane resistivity also strongly depends on the doping : the more metallic samples are obtained for the largest carrier concentration, i.e. the smaller S value. The combination of these two factors leads to an important conclusion that the power factor is independent of the doping in these Bi-based materials converging to a unique value of 2.2plusmn0.3 muW/cmK2 at room temperature, which is not so trivial. We will discuss the origin of the almost unique value of 2.2plusmn0.3 muW/cmK2.
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Enhanced thermoelectric properties in a layered rhodium oxide with a trigonal symmetry
Physical Review B - Condensed Matter and Materials Physics, 2007Co-Authors: W. Kobayashi, Denis Pelloquin, S. Hébert, O. Pérez, Antoine MaignanAbstract:We have synthesized an original layered rhodium oxide in the Bi-Sr-Rh-O system with alternately stacked conductive RhOx layer and insulating (Bi0.75Sr0.25)O1.5 fluorite-type layers. Thermopower, resistivity, Hall coefficient, magnetoresistance, and magnetization measurements evidence high thermoelectric properties with Pauli-like paramagnetism and large carrier concentration (∼1022 cm−3). The room-temperature resistivity, thermopower, and power factor are 1.6 mΩ cm, 63 μV∕K, and 2.48 μW∕cm K2, respectively, which are comparable with those of the best existing p-type thermoelectric Oxides, the misfit-layered Cobalt Oxides with the hexagonal CdI2-type CoO2 layer. In these crystals, the temperature dependence of the resistivity and the magnetic susceptibility suggest the presence of strong electron-electron interaction. This two-dimensional material emphasizes the potential of the transition-metal Oxides for thermoelectric applications.
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scaling behavior in thermoelectric misfit Cobalt Oxides
Physical Review Letters, 2006Co-Authors: P. Limelette, Raymond Frésard, Ch Simon, S. Hébert, V. Hardy, Antoine MaignanAbstract:We investigate both thermoelectric and thermodynamic properties of the misfit Cobalt oxide [Bi$_{1.7}$Co$_{0.3}$Ca$_{2}$O$_{4}$]$^{RS}_{0.6}$CoO$_{2}$. A large negative magnetothermopower is found to scale with both magnetic field and temperature revealing a significant spin entropy contribution to thermoelectric properties giving rise to a constant S$_0\approx$ 60 $\mu$V K$^{-1}$ equal to the high temperature asymptotic value of the spin 1/2 entropy. Low temperature specific heat measurements allow us to determine an enhanced electronic part with $\gamma\approx$ 50 mJ (mol K$^{2}$)$^{-1}$ attesting of strong correlations. Thereby, a critical comparison between [Bi$_{1.7}$Co$_{0.3}$Ca$_{2}$O$_{4}$]$^{RS}_{0.6}$CoO$_{2}$, other Cobaltites as well as other materials reveals a universal behavior of the thermopower low temperature slope as a function of $\gamma$ testifying thus a purely electronic origin. This potentially generic scaling behavior suggests here that the high room temperature value of the thermopower in misfit Cobalt Oxides results from the addition of a spin entropy contribution to an enlarged electronic one.
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Scaling behavior in thermoelectric misfit Cobalt Oxides
Physical Review Letters, 2006Co-Authors: P. Limelette, Raymond Frésard, Ch Simon, S. Hébert, V. Hardy, Antoine MaignanAbstract:We investigate both thermoelectric and thermodynamic properties of the misfit Cobalt oxide [Bi1.7Co0.3Ca2O4]RS0.6CoO2. A large negative magnetothermopower is found to scale with both magnetic field and temperature, revealing a significant spin entropy contribution to thermoelectric properties giving rise to a constant S0 approximately 60 microV K-1. Specific heat measurements allow us to determine an enhanced electronic part with gamma approximately 50 mJ (mol K2)-1 attesting to strong correlations. Thereby, the comparison between Cobaltites and other materials reveals a universal behavior of the thermopower slope as a function of gamma, testifying to a purely electronic origin. This potentially generic scaling behavior suggests here that the high room temperature value of the thermopower in misfit Cobalt Oxides results from the addition of a spin entropy contribution to an enlarged electronic one.
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Cobalt Oxides as potential thermoelectric elements: The influence of the dimensionality
Proceedings ICT'03. 22nd International Conference on Thermoelectrics (IEEE Cat. No.03TH8726), 2003Co-Authors: S. Hébert, Denis Pelloquin, Antoine Maignan, C. Martin, D. Flahaut, J. HejtmanekAbstract:2D misfit Cobalt Oxides combine a metallic behaviour at room temperature with a large thermopower, close to +90- +165/spl mu/V/K depending on the composition. High temperature measurements have shown that these good properties persist up to 800K, which makes them interesting for high temperature applications as p-type legs. The results for the different misfit phases investigated will be presented. Other families of Cobalt Oxides with different kinds of structure, 1D or 2D, have been investigated in order to improve the figure of merit and to find n-type thermoelectric materials and some promising results will be shown. Also, measurements of manganese Oxides at high temperature have been made to show their potentiality as n-type legs.
L Petrov - One of the best experts on this subject based on the ideXlab platform.
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nanosized iron and iron Cobalt spinel Oxides as catalysts for methanol decomposition
Applied Catalysis A-general, 2006Co-Authors: Elina Manova, Tanya Tsoncheva, Daniela Paneva, I Mitov, K Tenchev, Claude Estournes, L PetrovAbstract:Abstract Nanosized iron and mixed iron–Cobalt Oxides supported on activated carbon materials and their bulk analogues prepared by thermal synthesis are studied by X-rays diffraction, Mossbauer spectroscopy, magnetic measurements and temperature programmed reduction. Their catalytic behavior in methanol decomposition to H 2 , CO and methane is tested. Phase transformations in the metal Oxides affected by the reaction medium are also investigated. Changes in the reaction mechanism of the methanol decomposition after the metal Oxides deposition on the support as compared to the bulk phases are discussed.
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mechanochemically synthesized nano dimensional iron Cobalt spinel Oxides as catalysts for methanol decomposition
Applied Catalysis A-general, 2004Co-Authors: Elina Manova, Tanya Tsoncheva, Daniela Paneva, I Mitov, K Tenchev, L PetrovAbstract:Abstract Iron–Cobalt spinel oxide nanoparticles with different Fe/Co ratios have been prepared by the combination of chemical precipitation with simultaneous ultrasonic treatment and subsequent mechanical milling. For comparison, their analogues obtained by thermal synthesis were also studied. Phase composition and structural properties of iron–Cobalt Oxides are investigated by X-ray diffraction and Moessbauer spectroscopy. Their catalytic behavior in methanol decomposition to CO and methane is tested. A well-defined effect of the preparation method and Fe/Co ratio on the reduction and catalytic properties of iron–Cobalt samples is established.
Maarit Karppinen - One of the best experts on this subject based on the ideXlab platform.
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parent of misfit layered Cobalt Oxides sr2o2 qcoo2
Chemistry of Materials, 2006Co-Authors: H Yamauchi, K Sakai, Takuro Nagai, Yoshio Matsui, Maarit KarppinenAbstract:Misfit-layered (ML) Cobalt Oxides of the general formula of [MmA2Om+2]qCoO2 have been proven to be efficient thermoelectric materials because the structure is capable in accommodating the two seemingly contradictory characteristics of high electrical conductivity and large thermoelectric power. They are also potential hosts for other oxymoron-like functions. The known phases all contain one or two square-planar MO (M = Co, Bi, Pb, Tl, etc.) layers sandwiched together with two AO (A = Ca, Sr, Ba, etc.) planes of square symmetry between two adjacent CoO2 layers of hexagonal symmetry. Here, we report the realization of the simplest (m = 0) ML phase forming in the Sr−Co−O system with the cation ratio Sr/Co = 1. Atomic-resolution transmission electron microscopy (TEM) imaging confirms for the new phase the parent three-layer crystal structure, SrO−SrO−CoO2, which is compatible with the formula of [Sr2O2]qCoO2. Electron diffraction reveals that the phase is rather commensurate, i.e. the “misfit parameter” q is ...
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oxygen nonstoichiometry and Cobalt valence in misfit layered Cobalt Oxides
Journal of Solid State Chemistry, 2004Co-Authors: Y Morita, Ichiro Terasaki, H Yamauchi, T. Fujii, K Sakai, J Poulsen, T Motohashi, Maarit KarppinenAbstract:Abstract The hexagonal CoO 2 layer is the main building unit of the newly established category of misfit-layered and related Oxides showing—as a general feature—excellent thermoelectric characteristics. Here we use high-quality samples of the three prototype phases, Na 0.77 CoO 2+ δ , Ca 3 Co 3.95 O 9+ δ and (Bi,Pb) 2 Sr 2 Co 2 O 8+ δ , and apply both precise wet-chemical redox analysis techniques and thermogravimetric annealing experiments to approach the not-yet-addressed questions concerning oxygen nonstoichiometry and the valence of Co in these phases. In terms of the oxygen-stoichiometry tunability, substantial variation in the overall oxygen content upon reducing/oxidizing annealing is observed only for Ca 3 Co 3.95 O 9+ δ . The valence of Co in all the samples is found to lie in a range of 3.0–3.3, being significantly lower than the commonly believed values of 3.3–3.5.
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oxygen content analysis of functional perovskite derived Cobalt Oxides
Journal of Materials Chemistry, 2002Co-Authors: Maarit Karppinen, M Matvejeff, K Salomaki, H YamauchiAbstract:We have evaluated the possible redox chemical methods for precisely determining the oxygen content in complex Cobalt Oxides that are being studied increasingly for their interesting electric and magnetic properties. For the evaluation, BaNdCo2O5 + δ and Sr2(Ca,Y)Co2O6 + δ phases are selected as reference materials to elucidate the capabilities of the different analysis methods. Two redox methods so far commonly applied, i.e. thermogravimetric H2 reduction and iodometric titration, are tested and two other, as yet unapplied, methods, i.e. cerimetric titration and Cu+/Cu2+ coulometric titration, are introduced for the analysis of functional Cobalt Oxides. The three different titration methods are found to reveal consistent values for the oxygen content with good reproducibility. The results of thermogravimetric H2 reduction analysis agree with the titration results but show a wider scattering. Of the four analytical methods, the Cu+/Cu2+ coulometric titration method is considered most recommendable, since it is precise and may, furthermore, be applied to e.g. Cu and Fe substituted Cobalt oxide samples.
Elina Manova - One of the best experts on this subject based on the ideXlab platform.
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nanosized iron and iron Cobalt spinel Oxides as catalysts for methanol decomposition
Applied Catalysis A-general, 2006Co-Authors: Elina Manova, Tanya Tsoncheva, Daniela Paneva, I Mitov, K Tenchev, Claude Estournes, L PetrovAbstract:Abstract Nanosized iron and mixed iron–Cobalt Oxides supported on activated carbon materials and their bulk analogues prepared by thermal synthesis are studied by X-rays diffraction, Mossbauer spectroscopy, magnetic measurements and temperature programmed reduction. Their catalytic behavior in methanol decomposition to H 2 , CO and methane is tested. Phase transformations in the metal Oxides affected by the reaction medium are also investigated. Changes in the reaction mechanism of the methanol decomposition after the metal Oxides deposition on the support as compared to the bulk phases are discussed.
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mechanochemically synthesized nano dimensional iron Cobalt spinel Oxides as catalysts for methanol decomposition
Applied Catalysis A-general, 2004Co-Authors: Elina Manova, Tanya Tsoncheva, Daniela Paneva, I Mitov, K Tenchev, L PetrovAbstract:Abstract Iron–Cobalt spinel oxide nanoparticles with different Fe/Co ratios have been prepared by the combination of chemical precipitation with simultaneous ultrasonic treatment and subsequent mechanical milling. For comparison, their analogues obtained by thermal synthesis were also studied. Phase composition and structural properties of iron–Cobalt Oxides are investigated by X-ray diffraction and Moessbauer spectroscopy. Their catalytic behavior in methanol decomposition to CO and methane is tested. A well-defined effect of the preparation method and Fe/Co ratio on the reduction and catalytic properties of iron–Cobalt samples is established.
S. Hébert - One of the best experts on this subject based on the ideXlab platform.
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Thermoelectric properties in the misfit-layered-Cobalt Oxides [Bi2A2O4][CoO2]b1/b2 (A=Ca, Sr, Ba, b1/b2=1.65, 1.82, 1.98) single crystals
2007 26th International Conference on Thermoelectrics, 2007Co-Authors: W. Kobayashi, Denis Pelloquin, S. Hébert, D Grebille, H. Muguerra, Antoine MaignanAbstract:Single crystals of different phases of misfit Cobalt Oxides have been synthesized. Using these materials, the intrinsic power factor has been determined. By combining thermopower S and Hall coefficient measurements, we will show how S can be tuned by doping in this family of materials, the doping being strongly dependent on the misfit ratio p=b1/b2 ([Bi2A2O4][CoO2]b1/b2 with A=Ca, Sr, Ba, b1/b2=1.65, 1.82, 1.98). The in-plane resistivity also strongly depends on the doping : the more metallic samples are obtained for the largest carrier concentration, i.e. the smaller S value. The combination of these two factors leads to an important conclusion that the power factor is independent of the doping in these Bi-based materials converging to a unique value of 2.2plusmn0.3 muW/cmK2 at room temperature, which is not so trivial. We will discuss the origin of the almost unique value of 2.2plusmn0.3 muW/cmK2.
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Enhanced thermoelectric properties in a layered rhodium oxide with a trigonal symmetry
Physical Review B - Condensed Matter and Materials Physics, 2007Co-Authors: W. Kobayashi, Denis Pelloquin, S. Hébert, O. Pérez, Antoine MaignanAbstract:We have synthesized an original layered rhodium oxide in the Bi-Sr-Rh-O system with alternately stacked conductive RhOx layer and insulating (Bi0.75Sr0.25)O1.5 fluorite-type layers. Thermopower, resistivity, Hall coefficient, magnetoresistance, and magnetization measurements evidence high thermoelectric properties with Pauli-like paramagnetism and large carrier concentration (∼1022 cm−3). The room-temperature resistivity, thermopower, and power factor are 1.6 mΩ cm, 63 μV∕K, and 2.48 μW∕cm K2, respectively, which are comparable with those of the best existing p-type thermoelectric Oxides, the misfit-layered Cobalt Oxides with the hexagonal CdI2-type CoO2 layer. In these crystals, the temperature dependence of the resistivity and the magnetic susceptibility suggest the presence of strong electron-electron interaction. This two-dimensional material emphasizes the potential of the transition-metal Oxides for thermoelectric applications.
-
scaling behavior in thermoelectric misfit Cobalt Oxides
Physical Review Letters, 2006Co-Authors: P. Limelette, Raymond Frésard, Ch Simon, S. Hébert, V. Hardy, Antoine MaignanAbstract:We investigate both thermoelectric and thermodynamic properties of the misfit Cobalt oxide [Bi$_{1.7}$Co$_{0.3}$Ca$_{2}$O$_{4}$]$^{RS}_{0.6}$CoO$_{2}$. A large negative magnetothermopower is found to scale with both magnetic field and temperature revealing a significant spin entropy contribution to thermoelectric properties giving rise to a constant S$_0\approx$ 60 $\mu$V K$^{-1}$ equal to the high temperature asymptotic value of the spin 1/2 entropy. Low temperature specific heat measurements allow us to determine an enhanced electronic part with $\gamma\approx$ 50 mJ (mol K$^{2}$)$^{-1}$ attesting of strong correlations. Thereby, a critical comparison between [Bi$_{1.7}$Co$_{0.3}$Ca$_{2}$O$_{4}$]$^{RS}_{0.6}$CoO$_{2}$, other Cobaltites as well as other materials reveals a universal behavior of the thermopower low temperature slope as a function of $\gamma$ testifying thus a purely electronic origin. This potentially generic scaling behavior suggests here that the high room temperature value of the thermopower in misfit Cobalt Oxides results from the addition of a spin entropy contribution to an enlarged electronic one.
-
Scaling behavior in thermoelectric misfit Cobalt Oxides
Physical Review Letters, 2006Co-Authors: P. Limelette, Raymond Frésard, Ch Simon, S. Hébert, V. Hardy, Antoine MaignanAbstract:We investigate both thermoelectric and thermodynamic properties of the misfit Cobalt oxide [Bi1.7Co0.3Ca2O4]RS0.6CoO2. A large negative magnetothermopower is found to scale with both magnetic field and temperature, revealing a significant spin entropy contribution to thermoelectric properties giving rise to a constant S0 approximately 60 microV K-1. Specific heat measurements allow us to determine an enhanced electronic part with gamma approximately 50 mJ (mol K2)-1 attesting to strong correlations. Thereby, the comparison between Cobaltites and other materials reveals a universal behavior of the thermopower slope as a function of gamma, testifying to a purely electronic origin. This potentially generic scaling behavior suggests here that the high room temperature value of the thermopower in misfit Cobalt Oxides results from the addition of a spin entropy contribution to an enlarged electronic one.
-
Cobalt Oxides as potential thermoelectric elements: The influence of the dimensionality
Proceedings ICT'03. 22nd International Conference on Thermoelectrics (IEEE Cat. No.03TH8726), 2003Co-Authors: S. Hébert, Denis Pelloquin, Antoine Maignan, C. Martin, D. Flahaut, J. HejtmanekAbstract:2D misfit Cobalt Oxides combine a metallic behaviour at room temperature with a large thermopower, close to +90- +165/spl mu/V/K depending on the composition. High temperature measurements have shown that these good properties persist up to 800K, which makes them interesting for high temperature applications as p-type legs. The results for the different misfit phases investigated will be presented. Other families of Cobalt Oxides with different kinds of structure, 1D or 2D, have been investigated in order to improve the figure of merit and to find n-type thermoelectric materials and some promising results will be shown. Also, measurements of manganese Oxides at high temperature have been made to show their potentiality as n-type legs.