High-Temperature Stability of Hot-Pressed Sr-Doped Ca3Co4O9

Madre, M. A.; Urrutibeascoa, I.; Garcia, Gustavo; Torres, Miguel; Sotelo, A.; Díez, J. C.

doi:10.1007/s11664-018-6748-x

Cited by 5 publications

(3 citation statements)

References 31 publications

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“…[6] The mismatch and weak connection between Ca 2 CoO and CoO 2 layers enhance phonon scattering, reduce thermal conductivity, and lead to significant anisotropy. [7] Due to its unique staggered structure, in order to improve the thermoelectric performance of Ca 3 Co 4 O 9 , the traditional method is to adjust the carrier concentration by doping ions at the Ca position [8][9][10][11][12] or Co position, [13][14][15][16] so as to affect the electric transport and phonon scattering. Another strategy is to add nano materials into Ca 3 Co 4 O 9 as the second phase.…”

Section: Introductionmentioning

confidence: 99%

Effect of carbon nanotubes addition on thermoelectric properties of Ca₃Co₄O₉ ceramics

Li¹,

Wu²,

Zhang³

et al. 2022

Chinese Phys. B

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Increasing the phonon scattering center by adding nanoparticles to thermoelectric materials is an effective method of regulating the thermal conductivity. In this study, a series of Ca3Co4O9/x wt.%CNTs (x=0, 3, 5, 7, 10) polycrystalline ceramic thermoelectric materials by adding carbon nanotubes (CNTs) were prepared with solgel method and cold-pressing sintering technology. The results of X-ray diffraction and field emission scanning electron microscopy show that the materials have a single-phase structure with high orientation and sheet like microstructure. The effect of adding carbon nanotubes to the thermoelectric properties of Ca3Co4O9 were systematically measured. The test results of thermoelectric properties show that the addition of carbon nanotubes reduce the electrical conductivity and Seebeck coefficient of the material. Nevertheless, the thermal conductivity of the samples with carbon nanotubes addition is lower than that of the samples without carbon nanotubes. At 625K, the thermal conductivity of Ca3Co4O9/10wt.%CNTs sample is reduced to 0.408Wm-1K-1, which is about 73% lower than that of the original sample. When the three parameters are coupled, the ZT value of Ca3Co4O9/3wt.%CNTs sample reaches 0.052, which is 29% higher than that of the original sample. This shows that an appropriate amount of carbon nanotubes addition can reduce the thermal conductivity of Ca3Co4O9 ceramic samples and improve their thermoelectric properties.

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Section: Introductionmentioning

confidence: 99%

Effect of carbon nanotubes addition on thermoelectric properties of Ca₃Co₄O₉ ceramics

Li¹,

Wu²,

Zhang³

et al. 2022

Chinese Phys. B

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“…Thermoelectric (TE) materials have the ability to directly transform temperature gradients into electrical power, thanks to the Seebeck effect. The efficiency of this conversion is normally quantified using the dimensionless figure of merit ZT, equal to S 2 T/ κ (in which S 2 / is also called the power factor, PF, representing the electrical performance), where S, , κ and T are the Seebeck coefficient (or thermopower), electrical resistivity, improved electrical properties in these cobaltites or in similar anisotropic ceramic systems, such as uniaxial hot-pressing (HP) [26], spark plasma sintering (SPS) [27], microwave sintering (MS) [28], (electrically assisted) laser floating zone melting ((EA)LFZ) [29,30] and reactive templated grain growth (TGG) [31]. These techniques have the main advantage of producing dense materials with very low electrical resistivity values, owing to the preferential alignment of the conducting planes with the direction of current flow.…”

Section: Introductionmentioning

confidence: 99%

Exploring the High-Temperature Electrical Performance of Ca3−xLaxCo4O9 Thermoelectric Ceramics for Moderate and Low Substitution Levels

et al. 2021

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Aliovalent substitutions in Ca3Co4O9 often result in complex effects on the electrical properties and the solubility, and impact of the substituting cation also depends largely on the preparation and processing method. It is also well-known that the monoclinic symmetry of this material’s composite crystal structure allows for a significant hole transfer from the rock salt-type Ca2CoO3 buffer layers to the hexagonal CoO2 ones, increasing the concentration of holes and breaking the electron–hole symmetry from the latter layers. This work explored the relevant effects of relatively low La-for-Ca substitutions, for samples prepared and processed through a conventional ceramic route, chosen for its simplicity. The obtained results show that the actual substitution level does not exceed 0.03 (x < 0.03) in Ca3−xLaxCo4O9 samples with x = 0.01, 0.03, 0.05 and 0.07 and that further introduction of lanthanum results in simultaneous Ca3Co4O9 phase decomposition and secondary Ca3Co2O6 and (La,Ca)CoO3 phase formation. The microstructural effects promoted by this phase evolution have a moderate influence on the electronic transport. The electrical measurements and determined average oxidation state of cobalt at room temperature suggest that the present La substitutions might only have a minor effect on the concentration of charge carriers and/or their mobility. The electrical resistivity values of the Ca3−xLaxCo4O9 samples with x = 0.01, 0.03 and 0.05 were found to be ~1.3 times (or 24%) lower (considering mean values) than those measured for the pristine Ca3Co4O9 samples, while the changes in Seebeck coefficient values were only moderate. The highest power factor value calculated for Ca2.99La0.01Co4O9 (~0.28 mW/K2m at 800 °C) is among the best found in the literature for similar materials. The obtained results suggest that low rare-earth substitutions in the rock salt-type layers can be a promising pathway in designing and improving these p-type thermoelectric oxides, provided by the strong interplay between the mobility of charge carriers and their concentration, capable of breaking the electron–hole symmetry from the conductive layers.

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“…This material was chosen for its good machinability and physical and chemical stability at high temperatures. 10 The machinability requirement is related to the main innovation of the structure, viz. a cut that divides the thermoelectric pellet into two segments joined by an upper section that is not affected by the mentioned cut, forming a section that resembles the Greek letter .…”

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confidence: 99%

Π Unileg Thermoelectric Structure for Cycling Robustness at High Temperature and Low Manufacturing Cost

Garcia¹,

Martínez-Filgueira²,

Urrutibeascoa

et al. 2019

Journal of Elec Materi

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Unileg-type thermoelectric generators have proven to be a good choice for hightemperature applications, because their composition from a single thermoelectric material avoids different thermal expansion coefficients, giving the structure good mechanical strength and increased lifespan during thermal cycling. These structures are usually composed of a thermoelectric pellet with metallic electrical conductors joining the hot and cold ends of consecutive pellets. The novel unileg structure described herein is designed to deal with one of the main issues with traditional devices, viz. the physical and chemical stability of the solder between the pellet and the conductor at the hot side. The material for which this structure is proposed is a p-type Ca 3 Co 4 O 9 semiconductor oxide, due to its chemical stability at high temperature and good machinability. This final requirement is related to the main innovation of the structure, viz. a partial cut that divides the pellet longitudinally, leaving two legs joined by an uncut section, forming a section similar to the letter . The metallic conductor stripe usually employed in unileg thermoelectric generator manufacturing is replaced by a coating of conductive material, in this case silver, on one of the legs resulting from the cut. Due to these operations, one of the legs is practically short-circuited and acts as an electrical conductor for the unileg structure, eliminating the need for soldering at the hot end of the pellet.

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High-Temperature Stability of Hot-Pressed Sr-Doped Ca3Co4O9

Cited by 5 publications

References 31 publications

Effect of carbon nanotubes addition on thermoelectric properties of Ca₃Co₄O₉ ceramics

Effect of carbon nanotubes addition on thermoelectric properties of Ca₃Co₄O₉ ceramics

Exploring the High-Temperature Electrical Performance of Ca3−xLaxCo4O9 Thermoelectric Ceramics for Moderate and Low Substitution Levels

Π Unileg Thermoelectric Structure for Cycling Robustness at High Temperature and Low Manufacturing Cost

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High-Temperature Stability of Hot-Pressed Sr-Doped Ca3Co4O9

Cited by 5 publications

References 31 publications

Effect of carbon nanotubes addition on thermoelectric properties of Ca3Co4O9 ceramics

Effect of carbon nanotubes addition on thermoelectric properties of Ca3Co4O9 ceramics

Exploring the High-Temperature Electrical Performance of Ca3−xLaxCo4O9 Thermoelectric Ceramics for Moderate and Low Substitution Levels

Π Unileg Thermoelectric Structure for Cycling Robustness at High Temperature and Low Manufacturing Cost

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Product

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About

Effect of carbon nanotubes addition on thermoelectric properties of Ca₃Co₄O₉ ceramics

Effect of carbon nanotubes addition on thermoelectric properties of Ca₃Co₄O₉ ceramics