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김참,백주영,David Humberto Lopez,김동환,김호영 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.71 No.-
We provided a Bi2Te3-polypyrrole hybrid material, in which energy band junction and phonon scatteringeffects should appear at the interface of the two components. The hybrid material exhibited increases inelectrical resistivity and the Seebeck coefficient due the energy band junction, thus retaining the powerfactor without loss, whereas showing a great reduction in thermal conductivity because of the phononscattering at the interface. This significant decoupling of electrical and thermal properties resulted inpredominantfigures of merit (ZTmax1.21 at 100 C and ZTave1.18 at 50–150 C) among n-type Bi2Te3or Bi2(Te,Se)3 materials previously reported.
김참,백주영,김동환,김종태,David Humberto Lopez,김태욱,김호영 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.60 No.-
A polycrystalline WSe2 nanocompound was produced via a brief thermal reaction between the atomic elements. It should grow along the in-plane direction with covalent bonds rather than along the through-plane direction with van der Waals forces, leading to both crystallographic and morphological anisotropies. Not only the anisotropies should structurally induce strong phonon scattering but they alleviate possible electron scattering at the van der Waals forces; thus, we greatly reduced thermal conductivity while minimizing electrical conductivity loss. The decoupled conductivities resulted in enhancement in figure of merit, by approximately 70% at 350 °C, thus affording a promising material for mid-temperature thermoelectric operations.
Kim, Cham,Jung, Su Yeol,Lopez, David Humberto,Kim, Dong Hwan,Kim, Hoyoung Elsevier 2018 Scripta materialia Vol.144 No.-
<P><B>Abstract</B></P> <P>We report significant enhancement in thermoelectric performance of n-type Bi<SUB>2</SUB>(Te,Se)<SUB>3</SUB> prepared via conventional melting process. We deposited chemically synthesized Ag nanoparticles onto Te-rich Bi<SUB>2</SUB>(Te,Se)<SUB>3</SUB> and sintered the resulting substance to obtain a bulk product. The Ag nanoparticles and excessive Te elements should be converted to interstitial and antisite defects in the product, respectively, which possibly interacted to vary thermoelectric transport properties of the product. We endeavored to balance the concentration of the defects to optimize the properties, and thus we strengthened phonon glass electron crystal characteristic of the product, resulting in the improvement in thermoelectric performance.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kim, Cham,Baek, Ju Young,Lopez, David Humberto,Kim, Dong Hwan,Kim, Hoyoung Elsevier 2019 Journal of industrial and engineering chemistry Vol.71 No.-
<P><B>Abstract</B></P> <P>We provided a Bi<SUB>2</SUB>Te<SUB>3</SUB>-polypyrrole hybrid material, in which energy band junction and phonon scattering effects should appear at the interface of the two components. The hybrid material exhibited increases in electrical resistivity and the Seebeck coefficient due the energy band junction, thus retaining the power factor without loss, whereas showing a great reduction in thermal conductivity because of the phonon scattering at the interface. This significant decoupling of electrical and thermal properties resulted in predominant figures of merit (ZT<SUB>max</SUB> ∼1.21 at 100°C and ZT<SUB>ave</SUB> ∼1.18 at 50–150°C) among n-type Bi<SUB>2</SUB>Te<SUB>3</SUB> or Bi<SUB>2</SUB>(Te,Se)<SUB>3</SUB> materials previously reported.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We strategized to hybridize Bi<SUB>2</SUB>Te<SUB>3</SUB> with polypyrrole to obtain a bulk-phase structure. </LI> <LI> The hybrid material decoupled the electrical and thermal properties. </LI> <LI> The decoupling effect induced the excellent thermoelectric (TE) performance as below. </LI> <LI> The hybrid material recorded ZT<SUB>max</SUB> ∼1.21 at 100°C and ZT<SUB>ave</SUB> ∼1.18 at 50–150°C. </LI> <LI> The highest TE performance was achieved among n-type Bi<SUB>2</SUB>Te<SUB>3</SUB> materials ever reported. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kim, Cham,Baek, Ju Young,Kim, Dong Hwan,Kim, Jong Tae,Lopez, David Humberto,Kim, Taewook,Kim, Hoyoung THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2018 JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY -S Vol.60 No.-
<P><B>Abstract</B></P> <P>A polycrystalline WSe<SUB>2</SUB> nanocompound was produced via a brief thermal reaction between the atomic elements. It should grow along the in-plane direction with covalent bonds rather than along the through-plane direction with van der Waals forces, leading to both crystallographic and morphological anisotropies. Not only the anisotropies should structurally induce strong phonon scattering but they alleviate possible electron scattering at the van der Waals forces; thus, we greatly reduced thermal conductivity while minimizing electrical conductivity loss. The decoupled conductivities resulted in enhancement in figure of merit, by approximately 70% at 350°C, thus affording a promising material for mid-temperature thermoelectric operations.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kim, Cham,Baek, Ju Young,Kim, Dong Hwan,Kim, Jong Tae,Lopez, David Humberto,Kim, Taewook,Kim, Hoyoung Elsevier 2017 Journal of Alloys and Compounds Vol.722 No.-
<P><B>Abstract</B></P> <P>We studied a polycrystalline p-type WSe<SUB>2</SUB> semiconductor for thermoelectric applications. The polycrystalline WSe<SUB>2</SUB> nanocompound was prepared via a thermal reaction process of tungsten and selenium elements and it was sintered to produce a bulk structure using spark plasma sintering equipment. The resulting bulk specimen showed different morphological aspects, in which we observed irregularly-shaped grains along the direction perpendicular to the sintering pressing direction (i.e., along transversal direction) while finding thin layers along the parallel direction (i.e., along longitudinal direction). The specimen recorded a significantly low longitudinal thermal conductivity possibly because longitudinal phonon transport should be hindered due to the thin layers. Electron transport along the longitudinal direction might not be greatly interrupted by the morphological characteristics because the specimen recorded high carrier mobility along the direction resulting in lower electrical resistivity than that of a single crystalline equivalent. The specimen also showed moderate carrier concentration, which led to a plausible Seebeck coefficient. Since the specimen exhibited the significantly low thermal conductivity with the electrical properties, it recorded a higher figure of merit than the equivalent, which is the highest thermoelectric performance for p-type WSe<SUB>2</SUB> in bulk phase ever developed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new thermal reaction process was devised for a polycrystalline WSe<SUB>2</SUB> nanocompound. </LI> <LI> The nanocompound showed morphological anisotropy led to decoupling of conductivities. </LI> <LI> The highest thermoelectric performance was done for bulk phase WSe<SUB>2</SUB> ever reported. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kim, Cham,Kim, Chang Eun,Baek, Ju Young,Kim, Dong Hwan,Kim, Jong Tae,Ahn, Ji Hyeon,Lopez, David Humberto,Kim, Hoyoung Elsevier 2016 Scripta materialia Vol.119 No.-
<P><B>Abstract</B></P> <P>Chemical reaction processes for thermoelectric nanomaterials have received a lot of attention because of subsequent small and uniform nanostructures, causing a remarkable reduction in thermal conductivity; however, they typically showed low electrical properties possibly due to contaminations by chemicals resulting in low ZT. We devised a new chemical process for synthesizing an n-type Bi<SUB>2</SUB>Te<SUB>2.7</SUB>Se<SUB>0.3</SUB> nanocompound without the chemicals causing potential contaminations. The product exhibited a predominant electrical conductivity while retaining the advantage of chemical reaction routes; thus, synergistic effect of the thermoelectric transport properties was greatly induced, resulting in the highest ZT among n-type Bi<SUB>2</SUB>Te<SUB>3</SUB> materials in bulk phase.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Kim, Cham,Kim, Chang Eun,Baek, Ju Young,Kim, Dong Hwan,Kim, Jong Tae,Ahn, Ji Hyeon,Lopez, David Humberto,Kim, Taewook,Kim, Hoyoung American Chemical Society 2016 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.55 No.19
<P>Various chemical reaction processes have been adopted to synthesize Bi2Te3 thermoelectric nanomaterials for achieving remarkably low thermal conductivities, but chemical contaminations were usually pointed out as flaws, severely deteriorating electrical conductivities. We devised a novel water-based chemical reaction process for a Bi2Te2.7Se0.3 nanocompound in which the possibility for chemical contaminations was reduced. We successfully synthesized a small and highly distributed Bi2Te2.7Se0.3 nanocompound with high purity and adequately packed it via a spark plasma sintering process to produce a nanobulk structure. The resulting nanobulk specimen exhibited a physical density as high as the theoretical one with highly distributed nanograins; thus,. we were able to obtain remarkably high electrical,conductivity while maintaining thermal: conductivity as lbw as possible. The synergistic effect was greatly induced between the transport properties;. thus, the highest reported figure of merit value was achieved for n-type Bi2Te3 in the bulk phase.</P>