https://scholar.dgist.ac.kr/handle/20.500.11750/1129 2026-04-04T09:01:23Z https://scholar.dgist.ac.kr/handle/20.500.11750/9529 Title: Dual defect system of tellurium antisites and silver interstitials in off-stoichiometric Bi2(Te,Se)3+Y causing enhanced thermoelectric performance Author(s): Kim, Cham; Lopez, David Humberto; Kim, Dong Hwan; Kim, Hoyoung Abstract: Enhancement in the thermoelectric performance of n-type Bi2(Te,Se)3 was accomplished by forming a dual defect system composed of Te- and Ag-related defects. Te-rich Bi2(Te,Se)3+y, which has antisite defects generated by an excess of Te, was prepared via a conventional melting process. We devised a one-pot process in which Ag nanoparticles were deposited onto the Te-rich Bi2(Te,Se)3+y as soon as they were chemically synthesized, followed by a sintering compaction; thus, we aimed at selective insertion of Ag atoms into the interstitial sites of the Te-rich Bi2(Te,Se)3+y. The resulting Ag interstitials interact with the Te antisite defects to vary the thermoelectric transport properties of the product. We endeavored to balance the concentration of the defects to maximize the phonon glass electron crystal (PGEC) characteristic of the product, resulting in excellent thermoelectric performance in low temperature regions-we achieved the highest ZT average values, below 150 °C (ZTave = 1.18 (25-100 °C) and 1.15 (25-150 °C)), ever reported for n-type Bi2(Te,Se)3 materials. © 2019 The Royal Society of Chemistry. 2018-12-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/9496 Title: Decoupling effect of electrical and thermal properties of Bi2Te3-polypyrrole hybrid material causing remarkable enhancement in thermoelectric performance Author(s): Kim, Cham; Baek, Ju Young; Lopez, David Humberto; Kim, Dong Hwan; Kim, Hoyoung Abstract: We provided a Bi2Te3-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 (ZTmax ∼ 1.21 at 100 °C and ZTave ∼ 1.18 at 50–150 °C) among n-type Bi2Te3 or Bi2(Te,Se)3 materials previously reported. © 2018 The Korean Society of Industrial and Engineering Chemistry 2019-02-28T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/9377 Title: Interfacial energy band and phonon scattering effect in Bi2Te3-polypyrrole hybrid thermoelectric material Author(s): Kim, Cham; Baek, Ju Young; Lopez, David Humberto; Kim, Dong Hwan; Kim, Hoyoung Abstract: We hybridized n-type Bi2Te3 with an inexpensive and abundantly available conducting polymer, polypyrrole, to obtain a bulk-structured hybrid material in which the interfacial energy band and the phonon scattering effects should occur at the interface of the two components. The obtained hybrid material inevitably exhibited a lower electrical conductivity than pristine Bi2Te3, which may be attributable to carrier scattering at the interfacial energy barrier. However, the hybrid material completely compensated for this loss in electrical conductivity with a significant increase in the Seebeck coefficient, and thus it retained the power factor with no loss. In addition, the hybrid material displayed a much lower thermal conductivity than pristine Bi2Te3 owing to the phonon scattering effect. The hybrid material exhibited significant decoupling of the electrical and thermal properties, thus affording state-of-the-art figures of merit (ZT ∼ 0.98 at 25 °C, ZTmax ∼ 1.21 at 100 °C, and ZTave ∼ 1.18 at 50-150 °C) that exceed those of most of the previously reported n-type Bi2Te3 or Bi2(Te,Se)3 materials. © 2018 Author(s). 2018-09-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/9064 Title: Method for evaluating interfacial resistances of thermoelectric devices using I-V measurement Author(s): Kim, Dong Hwan; Kim, Cham; Kim, Jong Tae; Yoon, Duck Ki; Kim, Hoyoung Abstract: Research on the methodology for predicting and analyzing the performance of a thermoelectric device (TED) can offer various possibilities for enhancing its energy conversion characteristics. In this work, the methodology to determine the electrical contact resistance and the interfacial thermal resistance of a TED was studied. Based on one-dimensional heat transfer equations of power generation mode that includes electrical contact resistance and interfacial thermal resistance, we derived explicit expressions for the open circuit voltage and the short circuit current as the limiting cases of the external electrical load. The measurements of the open circuit voltage and the short-circuit current of TED were carried out for various thermal interface materials (TIMs) between the TED and heat reservoirs under varying compressive forces. The electrical contact resistance and the interfacial thermal resistance of a TED were determined by matching the measured values of the open circuit voltage and the short circuit current of a TED to the results of the analytic model. The electrical contact resistivity of the TED tested was approximately 3 × 10−9 Ωm2, irrespective of the compressive force, the hot-side temperature, and the TIMs. The interfacial thermal resistance varied sensitively with the TIMs and decreased with the compressive forces. © 2018 Elsevier Ltd 2018-11-30T15:00:00Z