Microstructural and Thermoelectric Characteristics of Zinc Oxide‐Based Thermoelectric Materials Fabricated Using a Spark Plasma Sintering Process

Kim, Kyoung Hun; Shim, Seung‐Bo; Shim, Kwang Bo; Niihara, Koichi; Hojo, Junichi

doi:10.1111/j.1551-2916.2005.00131.x

Cited by 104 publications

(66 citation statements)

References 25 publications

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“…In-doped nanobulk ZnO pellets show -250 ≤  300K ≤ -325 VK -1 with a maximum at 0.25 at.% In, while Bi doping yields -480 ≤  300K ≤ -530 VK -1 . These  300K values are 10-50% higher than reported for any standard thermoelectric samples of ZnO 5,24,25 . Uniquely, 0.5 at.% In doping yields a higher  300K than the non-nanostructured counterparts at comparably high n and .…”

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confidence: 52%

Heavy element doping for enhancing thermoelectric properties of nanostructured zinc oxide

et al. 2014

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ZnO is a high melting point high charge carrier mobility semiconductor with potential as a thermoelectric material, but its high thermal conductivity is the limiting factor for increasing the thermoelectric figure of merit ZT. Here, we demonstrate that doping ZnO with heavy elements can significantly enhance ZT. Indium doping leads to ultralow κ~3 Wm , yielding ZT 1000K ~ 0.45 that is ~80% higher than nonnanostructured In-Zn-O alloys. Although Bi doping also yields high Seebeck coefficient of α 300K~5 00 μVK -1 , Bi segregation, grain growth and defect complexing are unfavorable for increasing ZT. Thus, besides increased impurity scattering of phonons, the concurrence of nanostructuring and charge carrier concentration control is key to ZT enhancement. Our results open up a new means to realize high ZT thermoelectric nanomaterials based on ZnO.Keywords: Nanobulk thermoelectrics, indium doping, bismuth doping, zinc oxide, first principle transport calculations, high figure of merit ZT This is an author-produced, peer-reviewed version of this article. The final, definitive version of this document can be found online at RCS Advances, published by The Royal Society of Chemistry: RSC Publishing. Copyright restrictions may apply. DOI: 10.1039/c3ra46813e 2 Table of Contents FigureHigh efficiency thermoelectric devices offer great potential for harvesting waste heat into electricity 1 , but require materials with thermoelectric figure of merit ZT>1 above 600 K. We recapitulate that ZT is defined as  2 /  is the Seebeck coefficient,  is the electrical conductivity and  is the thermal conductivity, and the numerator  2  is also known as the power factor. Zinc oxide 2 and its alloys are attractive candidates because of their high thermal stability, corrosion resistance, low-cost, and non-toxicity. But, unlike low bandgap semiconductor thermoelectrics with complex crystal structures and heavy elements, ZnO is composed of light elements and has a 3.3 eV bandgap and a relatively simple wurtzite structure. In contrast to conventional thermoelectric materials, which typically have heavy band features, n-type ZnO has a singly degenerate s-electron conduction band, with a low effective mass, m * =0.24m e , and high mobility. Thus, even though ZnO can exhibit a high Seebeck coefficient 3,4 it does so at low carrier concentrations. In general, the Wiedemann Franz relation can be used to write ZT= r 2 /L, where L is the effective Lorentz number and r= e /, where κ is the sum of a lattice part κ L and an electronic part κ e . Good thermoelectrics have sizeable values of the ratio r at carrier concentrations where  is also high. In ZnO, the lattice thermal conductivity is generally too high (e.g.,  L~~5 Wm -1 K -1 at 1000 K) 5 to achieve high values of r. Lowering  L by nanostructuring combined with tapping into local strain effects, e.g., arising from the anisotropic thermal expansion 6 , will be essential to realize high ZT in ZnO-based materials. The challenge with decreasing  L by nanostructuring alone ...

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Heavy element doping for enhancing thermoelectric properties of nanostructured zinc oxide

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“…The retardation of ZnO grain growth may be due to the pinning by dispersed ZnAl 2 O 4 particles. 4 As seen at points 3 and 4, the bent of grain boundaries means the pinning. According to the above result, the fine distribution of ZnAl 2 O 4 seemed to be achieved in powder mixing method rather than in colloidal method.…”

Section: Crystalline Phases Of Zno Sintered Bodymentioning

confidence: 99%

“…Kim et al 4 reported that 1 atomic! Al did not fully dissolve into ZnO structure because of limited solubility, therefore, excess Al reacted with ZnO to form ZnAl 2 O 4 phase.…”

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Distribution and Solubility Limit of Al in Al2O3-Doped ZnO Sintered Body

Shirouzu

Ohkusa²,

Hotta

et al. 2007

J. Ceram. Soc. Japan

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A few mol! Al 2 O 3 -doped ZnO sintered body forms a substitutional solid solution and the semi-conducting property is drastically affected by the content of the dissolved Al. It was suggested from the results of XRD and EPMA that Al existed in the ZnO sintered body in the form of ZnAl 2 O 4 . Furthermore, the distribution of ZnAl 2 O 4 was visualized by AFM and SEM. It was, however, difficult for these techniques to detect dissolved Al in ZnO grains directly. The SIMS mapping suggested that the trace amount of Al approximately 0.3 atomic! dissolved into ZnO grains because of high sensitivity for trace impurities. This result was consistent with the change in lattice constants of ZnO with Al dissolution.

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“…Material family References Mn oxide [49][50][51][52][53][54][55][56][57][58][59][60] ZnO, SrTiO 3 33, [61][62][63][64][65][66][67][68][69][70][71][72] Co oxide 34,35,[73][74][75][76][77] other oxide 28,63,[78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95][96] Si-Ge …”

Section: Acknowledgementmentioning

confidence: 99%

Data-Driven Review of Thermoelectric Materials: Performance and Resource Considerations

et al. 2013

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In this review, we describe the creation of a large database of thermoelectric materials prepared by abstracting information from over 100 publications. The database has over 18 000 data points from multiple classes of compounds, whose relevant properties have been measured at several temperatures. Appropriate visualization of the data immediately allows certain insights to be gained with regard to the property space of plausible thermoelectric materials. Of particular note is that any candidate material needs to display an electrical resistivity value that is close to 1 mW cm at 300 K, i.e., samples should be significantly more conductive than the Mott minimum metallic conductivity. The Herfindahl-Hirschman index, a commonly accepted measure of market concentration, has been calculated from geological data (known elemental reserves) and geopolitical data (elemental production) for much of the periodic table. The visualization strategy employed here allows rapid sorting of thermoelectric compositions with respect to important issues of elemental scarcity and supply risk.

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Microstructural and Thermoelectric Characteristics of Zinc Oxide‐Based Thermoelectric Materials Fabricated Using a Spark Plasma Sintering Process

Cited by 104 publications

References 25 publications

Heavy element doping for enhancing thermoelectric properties of nanostructured zinc oxide

Heavy element doping for enhancing thermoelectric properties of nanostructured zinc oxide

Distribution and Solubility Limit of Al in Al2O3-Doped ZnO Sintered Body

Data-Driven Review of Thermoelectric Materials: Performance and Resource Considerations

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