Electrorefining Characteristics of Uranium by Using a Graphite Cathode

Youngho Kang,JongHyeon Lee,Sungchan Hwang,JoonBo Shim,EungHo Kim 한국방사성폐기물학회 2007 방사성폐기물학회지 Vol.5 No.1

흑연음극을 이용하여 LiCl-KCl공융염내에서 금속우라늄의 전해정련을 수행하였다. Uraniurn-Graphite Intercalation Compound(U-GIC)의 형성에 의하여 우라늄 전착물의 sell-scraping이 일어나며 전해정련에서 stripping과정을 생략함으로서 전해효율을 높일 수 있다. 우라늄 전착물내의 희토류 원소 오염은 무시할 만 하였으나 약 300ppm정도의 탄소가 오염되어 있는 것으로 관찰되었다. 탄소 오염은 이트륨을 이용한 정제공정 등을 거칠 경우 제거 가능하리라 사료된다. 회수된 우라늄 전착물의 조직 특성을 분석하였으며, 스틸 음극에 의해 회수된 전착물과 비교하였다. 이 결과는 초기 실험결과 이며 보다 심층적 연구를 통하여 사용 후 금속핵연료의 전해정련 개념을 개선시킬 수 있을 것으로 판단된다. Electrorefining experiments were successfully carried out in LiCl-KCl eutectic molten salt with a graphite cathode. It was found that the formation of Uranium-Graphite intercalation compound(U-GIC) helped the self-scraping mechanism of the uranium dendrite and the efficiency of the electrorefiner increased due to an elimination of the stripping step. The contaminations of the uranium deposit by rare earth elements was negligible while about 300 ppm of carbon was observed. The carbon contamination is believed to be eliminated by further purification by yttrium reaction. The morphology characteristics of the recovered U deposit was compared to that of steel cathode. These are only qualitative preliminary experimental results, but we believe that further research on this type of activity change the direction of the electrorefining research on spent nuclear fuel.

Influence of wave-function updates inGWcalculations on titanates

Kang, Gijae,Kang, Youngho,Han, Seungwu American Physical Society 2015 Physical review. B, Condensed matter and materials Vol.91 No.15

First-Principles Study on Doping of Copper Halides

Kang Youngho 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.9

We investigate the doping behavior of copper halides CuX (X = Cl, Br, and I) by using density functional theory calculations. We evaluate the formation energies of Cu and X vacancies, which reveal the formation of Cu vacancies to be energetically favorable when the Fermi level is near the valence band maximum, leading to the p-type conductivity of CuX. The possible hole concentration of CuX due to the formation of vacancies is predicted to decrease from CuI to CuBr and CuCl, consistent with experiments. We also study hydrogen interstitials, which show that the p-type conductivity of CuX, especially CuCl, can be undermined due to compensation of holes by hydrogen interstitials. By inspecting the band offset of CuX, we provide fundamental insights into the X dependence of p-type doping in CuX.

Ab initiocalculation of ionization potential and electron affinity in solid-state organic semiconductors

Kang, Youngho,Jeon, Sang Ho,Cho, Youngmi,Han, Seungwu American Physical Society 2016 Physical Review B Vol.93 No.3

An origin of unintentional doping in transition metal dichalcogenides: the role of hydrogen impurities

Kang, Youngho,Han, Seungwu The Royal Society of Chemistry 2017 Nanoscale Vol.9 No.12

<P>We theoretically elucidate the origin of unintentional doping in two-dimensional transition-metal dichalcogenides (TMDs), which has been consistently reported by experiment, but which still remains unclear. Our explanation is based on the charge transfer between TMDs and the underlying SiO2 in which hydrogen impurities with a negative-U property pin the Fermi level of the SiO2 as well as adjacent TMD layers. Using first-principles calculations, we obtain the pinning point of the Fermi level from the charge transition level of the hydrogen in the SiO2, epsilon(+/-), and align it with respect to the band-edge positions of monolayer TMDs. The computational results show that the Fermi levels of TMDs estimated by epsilon(+/-) successfully explain the conducting polarity (n-or p-type) and relative doping concentrations of thin TMD films. By enlightening on the microscopic origin of unintentional doping in TMDs, we believe that the present work will contribute to precise control of TMD-based electronic devices.</P>

Weak dependence of spontaneous polarization on epitaxial strain in ferroelectric BiAlO3: A first-principles study

Kang Youngho 한국물리학회 2022 Current Applied Physics Vol.35 No.-

We investigate the effects of epitaxial strain on the ferroelectric properties of BiAlO3 (BAO) using first-principles calculations. We find a large polarization (P) of 72.3 μC/cm2 as well as a small energy barrier of ~0.1 eV/formula unit for coherent ferroelectric switching of unstrained BAO. Thus, this material is suitable for applications in high-speed nonvolatile memory. We study the modification of P due to epitaxial strains of − 5 to +5%, where the minus and plus signs represent the compressive and tensile strains, respectively. The polarization of BAO is insensitive to epitaxial strain; the polarization change is limited to below ~6%. The weak sensitivity of the polarization is attributed to the stereochemical activity of Bi 6s2 lone pairs as well as the inertness of the B-site Al to the polarization. The strain application modifies the switching energy barrier by up to 30%, which provides guidelines for design of devices based on BAO.

Computational Screening of Indirect-Gap Semiconductors for Potential Photovoltaic Absorbers

Kang, Youngho,Youn, Yong,Han, Seungwu,Park, Jiwon,Oh, Chang-Seok American Chemical Society 2019 Chemistry of materials Vol.31 No.11

<P>Photovoltaic (PV) absorbers are key components of PV cells used to harvest solar energy, which is an attractive renewable energy resource. In this study, a high-throughput computational screening is conducted to discover potential PV absorbers. While direct-gap semiconductors are usually favored as PV absorbers, herein, we focus on indirect-gap semiconductors that could exhibit a long lifetime of photocarriers because of the low probability of band-to-band recombination, enabling high-performance PV cells. From the Materials Project database, we screen semiconductors considering the direct band gap, the difference between the direct and indirect band gaps, and the effective mass of carriers as selection metrics. Taking low costs and earth abundance of constituent elements into account, we suggest GeAs<SUB>2</SUB>, SiAs<SUB>2</SUB>, and NaSbS<SUB>2</SUB> as particularly promising indirect-gap semiconductors. Their absorption and defect properties are analyzed in detail, providing a route to engineering materials with high efficiency.</P> [FIG OMISSION]</BR>

GWcalculations on post-transition-metal oxides

Kang, Youngho,Kang, Gijae,Nahm, Ho-Hyun,Cho, Seong-Ho,Park, Young Soo,Han, Seungwu American Physical Society 2014 Physical review. B, Condensed matter and materials Vol.89 No.16

In order to establish the reliable GW scheme that can be consistently applied to post-transition-metal oxides (post-TMOs), we carry out comprehensive GW calculations on electronic structures of ZnO, Ga2O3, In2O3, and SnO2, the four representative post-TMOs. Various levels of self-consistency (G(0)W(0), GW(0), and QPGW(0)) and different starting functionals (GGA, GGA + U, and hybrid functional) are tested and their influence on the resulting electronic structure is closely analyzed. It is found that the GW0 scheme with GGA + U as the initial functional turns out to give the best agreement with experiment, implying that describing the position of metal-d level precisely in the ground state plays a critical role for the accurate dielectric property and quasiparticle band gap. Nevertheless, the computation on ZnO still suffers from the shallow Zn-d level and we propose a modified approach (GW(0) + U-d) that additionally considers an effective Hubbard U term during GW0 iterations and thereby significantly improves the band gap. It is also shown that a GGA + U-based GW0(+ Ud) scheme produces an accurate energy gap of crystalline InGaZnO4, implying that this can serve as a standard scheme that can be applied to general structures of post-TMOs.

Interaction among New Firm Formation, Privatization, and Business Environment in Transition Countries

Youngho Kang,ByungYeon Kim,JongKyu Lee 서울대학교 경제연구소 2017 Seoul journal of economics Vol.30 No.2

The formation of new private firms can facilitate transition from socialism to a market economy. This study uses data from transition economies to investigate the effects of large-scale privatization and the barriers to the establishment of new firms. It finds that large-scale privatization positively affects the formation of new firm, but such effects disappear as the costs of start-up increase. These results imply that both privatization and favorable business environments are necessary for firm creation.

Firm Size and Public Policies for Business R&D Expenditures in OECD Countries

Youngho Kang(강영호) 고려대학교 미래성장연구소 2017 미래성장연구 Vol.3 No.1

민간 연구개발 지출을 증진시키기 위해, OECD국가들은 연구개발 조세지원, 연구개발 보조금 지원, 또는 두 가지 지원책을 사용하고 있다. 이 정책들을 지원하는 예산은 제한적이기 때문에, 어떤 정책이 민간 연구개발 지출을 더욱 촉진시키는 지는 정책 결정자에게 중요한 질문이다. 이 연구에는 실증분석으로 연구개발의 두 가지 지원정책들이 기업규모에 따라 다른 효과가 있음을 보였다. 특히, 연구개발 보조금 지원은 종사자 49명 이하의 규모를 가진 기업들의 연구개발 지출을 통계적으로 유의하게 증가시킨 반면, 연구개발 조세지원은 종사자 250명 이상 기업들의 연구개발 지출을 유의하게 증가시켰다. To foster business R&D expenditures, OECD countries have used either R&D tax incentives or R&D subsidies, or both. Because of a limited fiscal budget to implement policies, an important question for policy makers is which policy is effective to stimulate business R&D. The empirical findings in this paper show that the effects of the two policy instruments are different according to firm size. Specifically, R&D subsidies affect positively and significantly the business R&D expenditure in the group of firms with less 49 employees, whereas R&D tax incentives significantly and positively affect those firms that have more than 250 employees.