• Review

    Failure Cases according to Photocuring-Based Alumina 3D Printing
    So-Young Ko, Shin-Il Go, Kyoung-Jun Jang, Sang-Jin Lee
    3D printing using ceramic powder to produce precision ceramic parts has been studied with various additive manufacturing methods. This study analyzed problems … + READ MORE
    3D printing using ceramic powder to produce precision ceramic parts has been studied with various additive manufacturing methods. This study analyzed problems occurring in alumina additive manufacturing that uses digital light processing (DLP) as well as methods to address such problems. For efficient analysis, we have classified alumina additive manufacturing into three types according to the driving method of the build platform - lifting type (LT), tilting type (TT) of the vat, and blade movement type (BT). LT had a problem with detachment and cracking of the alumina green body. However, this could be prevented by carefully controlling the cure depth of the suspension slurry and the bonding force between layers and improving the material used for coating the vat. TT, which resulted in non-uniform alumina additive manufacturing, could be improved by modifying the bidirectionality of the axis and the fluidity of the highly viscous alumina suspension slurry. BT resulted in detachment of the specimen as well as non-uniform results, but this could be avoided by shortening the shifting distance of the alumina suspension when it is introduced to the build platform, and enabling effective spreading. - COLLAPSE
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    27 October 2024

  • Research Paper

    Thermal Transport Properties of a Mixed Anion Layered Compound, Polycrystalline LaCu1-δS0.5Se0.5O (δ = 0.01)
    Nobuhiko Azuma, Hiroki Sawada, Hirotaka Ito, Ryosuke Sakagami, Yuya Tanaka, Tatsuhide Fujioka, Masanori Matoba, Yoichi Kamihara
    Electrical and thermal transport properties of a polycrystalline carrier-doped wide-gap semiconductor LaCu1-δS0.5Se0.5O (δ = … + READ MORE
    Electrical and thermal transport properties of a polycrystalline carrier-doped wide-gap semiconductor LaCu1-δS0.5Se0.5O (δ = 0.01), in which the CuCh (Ch = S, Se) layer works as conducting layer, were measured at temperatures 473~673 K. The presence of δ = 0.01 copper defects dramatically reduces the electrical resistivity (ρ) to approximately one part per million compared to that of δ = 0 at room temperature. The polycrystalline δ = 0.01 sample exhibited ρ of 1.3 × 10-3 Ωm, thermal conductivity of 6.0 Wm-1 K-1, and Seebeck coefficient (S) of 87 µVK-1 at 673 K. The maximum value of the dimensionless figure of merit (ZT) of the δ = 0.01 sample was calculated to be 6.4 × 10-4 at T = 673 K. The ZT value is far smaller than a ZT ~ 0.01 measured for a nominal LaCuSeO sample. The smaller ZT is mainly due to the small S measured for LaCu1-δS0.5Se0.5O (δ = 0.01). According to the Debye model, above 300 K phonon thermal conductivity in a pure lattice is inversely proportional to T, while thermal conductivity of the δ = 0.01 sample increases with increasing T. - COLLAPSE
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    27 October 2024

  • Research Paper

    Heat Treatment Optimization of Small-Sized Lithium Nickel Oxide Using Precursors Synthesized by Glycine as Chelating Agent
    Nayun Kim, Chunjoong Kim
    Lithium-ion batteries are widely used in various advanced devices, including electric vehicles and energy storage devices. As the application range of lithium-ion … + READ MORE
    Lithium-ion batteries are widely used in various advanced devices, including electric vehicles and energy storage devices. As the application range of lithium-ion batteries expands, it will be increasingly important to improve their gravimetric and volumetric energy density. Layer-structured oxide materials have been widely adopted as cathode materials in Li-ion batteries. Among them, LiNiO2 has attracted interest because of its high theoretical capacity, ~274 mAh g-1, assuming reversible one Li+-(de)intercalation from the structure. Presently, such layered structure cathode materials are prepared by calcination of precursors. The precursors are typically hydroxides synthesized by coprecipitation reaction. Precursors synthesized by coprecipitation reaction have a spherical morphology with a size larger than 10 µm. Spherical precursors in the several micrometer range are difficult to obtain due to the limited coprecipitation reaction time, and can lead to vigorous collisions between the precursor particles. In this study, spherical and small-sized Ni(OH)2 precursors were synthesized using a new synthesis method instead of the conventional precipitation method. The highest capacity, 170 mAh g-1, could be achieved in the temperature range of 730~760 °C. The improved capacity was confirmed to be due to the higher quality of the layered structure. - COLLAPSE
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    27 October 2024

  • Research Paper

    Synthesis of Iron Phosphate Via Coprecipitation Method for LiFePO4 Cathode
    Jeongwoo Lim, Seokwon Seo, Chunjoong Kim
    In this study, ferric phosphate precursors were prepared by controlling precipitation time, and the resulting LiFePO4 active materials were thoroughly investigated. … + READ MORE
    In this study, ferric phosphate precursors were prepared by controlling precipitation time, and the resulting LiFePO4 active materials were thoroughly investigated. Microscale LiFePO4 cathode materials, designed for high energy density at the cell level, were successfully synthesized through a 10 h co-precipitation. As the reaction time increased, smaller primary particles were aggregated more tightly, and the secondary particles exhibited a more spherical shape. Meanwhile, ammonia did not work effectively as a complexing agent. The carbon coated LiFePO4 (LiFePO4/C) synthesized from the 10 h ferric phosphate precursor exhibited larger primary and secondary particle sizes, a lower specific surface area, and higher crystallinity due to the sintering of the primary particles. Enhanced battery performance was achieved with the LiFePO4/C that was synthesized from the precursor with the smaller size, which exhibited the discharge capacity of 132.25 mAh ‧ g-1 at 0.1 C, 70 % capacity retention at 5 C compared with 0.1 C, and 99.9 % capacity retention after the 50th cycle. The better battery performance is attributed to the lower charge transfer resistance and higher ionic conductivity, resulting from smaller primary particle sizes and a shorter Li+ diffusion path. - COLLAPSE
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    27 October 2024

  • Research Paper

    Improvement on Encapsulation Properties of Solar Cells Via Low-Temperature Atomic Layer Deposition

    저온 원자층 증착 공정을 통한 태양전지 봉지층 특성 향상

    Ho Jae Ki, Yong Tae Kim, Sang Won Lee, Jaeyeong Heo

    기호재, 김용태, 이상원, 허재영

    Perovskite-based solar cells have recently exhibited rapid improvement in power conversion efficiency due to their high optical and electrical properties. However, perovskite … + READ MORE
    Perovskite-based solar cells have recently exhibited rapid improvement in power conversion efficiency due to their high optical and electrical properties. However, perovskite materials are fundamentally degraded by heat and moisture, making long-term stability a critical issue. One way to improve the stability of perovskite solar cells is to encapsulate them. However, a low temperature encapsulation process of less than 100 °C is needed to minimize degrading the perovskite materials. High moisture barrier properties are also required. To realize a high performance encapsulation layer at low temperature we employed atomic layer deposition (ALD) technique. As the encapsulation layer materials, Al2O3, which is most commonly used due to its high density and optical properties, and SnO2, which is mainly used as an electron transport layer in perovskite solar cells, were selected. Single film and multi-layer structured films of Al2O3 and SnO2 were deposited, and the structural, optical, and moisture permeability properties were investigated. - COLLAPSE
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    27 October 2024

  • Research Paper

    Boryeong Mud-Derived Silicon-Oxides Composite Anodes with Excellent Cycling Stability for Lithium-Ion Batteries

    보령 머드로부터 제조한 우수한 수명 안정성의 실리콘계 음극 소재

    Yun A Kim, Jae-Won Lee

    김윤아, 이재원

    Silicon-based anode materials have attracted significant interest because of their advantages, including high theoretical specific capacity (~4,200 mAh/g), low working potential (0.4 … + READ MORE
    Silicon-based anode materials have attracted significant interest because of their advantages, including high theoretical specific capacity (~4,200 mAh/g), low working potential (0.4 V vs Li/Li+), and abundant sources. However, their significant initial capacity loss and large volume changes during cycling impede the application of silicon-based anodes in lithium-ion batteries. In this work, we propose a silicon oxide (SiOx) anode material for lithium-ion batteries produced with a magnesio-thermic reduction (MTR) process adopting Boryeong mud as a starting material. Boryeong mud contains various minerals such as clinochlore [(Mg,Fe)6(Si,Al)4O10(OH)8], anorthite (CaAl2Si2O8), illite [K0.7Al2(Si,Al)4O10(OH)2], and quartz (SiO2). The MTR process with Boryeong mud generates a mixture of amorphous silicon oxides (SiOx and SiO2), and magnesium aluminate which helps to alleviate the volume expansion of the electrode during charge/discharge. To observe the effects of these oxides, we conducted various analyses including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-Transformation infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) and cyclic voltammetry (CV) galvanic cell testing. The amorphous SiO2 and MgAl2O4 suppressed the volume expansion of the silicon-based anode, and excellent cycle performance was achieved as a result. - COLLAPSE
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    27 October 2024

  • Research Paper

    Structural and Electrical Properties of Al-Co(Al-N)/AlN-Co Multilayer Films Prepared by Two-Facing-Target Type Sputtering System

    대향 타겟형 스퍼터링 시스템으로 제작한 Al-Co(Al-N)/AlN-Co 다층 박막의 구조 및 전기적 특성

    Chang-Suk Han, Chang-Hwan Bae

    한창석, >배창환

    High-frequency soft magnetic Ni, Fe, and Co-based thin films have been developed, typically as nanocrystals and amorphous alloys. These Ni, Fe, and … + READ MORE
    High-frequency soft magnetic Ni, Fe, and Co-based thin films have been developed, typically as nanocrystals and amorphous alloys. These Ni, Fe, and Co-based thin films exhibit remarkably good frequency dependence up to high frequencies of several tens of MHz. These properties arise from the moderate magnetic anisotropy and fairly high electrical resistivity that result from the microstructural characteristics of the nanocrystalline and amorphous states. In this paper, Al-Co/AlN-Co and Al-N/AlN-Co multilayer films were deposited using two-facing-target type sputtering (TFTS). Their microstructures, magnetic and electrical properties were studied with the expectation that inserting Al-Co or Al-N as an interlayer could effectively reduce the coercive force and produce films with relatively high resistivity. A new approach is presented for the fabrication of Al-Co(Al-N)/AlN-Co multilayer films, prepared with the TFTS system. The deposited films were isothermally annealed at different temperatures and investigated for microstructure, magnetic properties and resistivity. The TFTS method used in this experiment is suitable for fabricating Al-Co(Al-N)/AlN-Co multilayer films with different layer thickness ratio (LTR). The annealing conditions, thickness of the multilayer film, and LTR can control the physical properties as well as the microstructure of the manufactured film. Magnetization and resistance increased and coercivity decreased as LTR decreased. The thin film with LTR = 0.175 exhibited high resistivity values of 2,500 µΩ-cm, magnetization of 360 emu/cm3, and coercivity of 5 Oe. Results suggests that thin films with such good resistivity and magnetization would be useful as high-density recording materials. - COLLAPSE
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    27 October 2024

  • Research Paper

    Analysis of the Improvement of Photoelectrical Properties of Cu2ZnSn(S, Se)4 Thin Film and Solar Cells Via Cation Doping

    양이온 도핑을 통한 Cu2ZnSn(S, Se)4 박막의 광전기적 특성 향상 및 이를 적용시킨 박막 태양전지의 효율 향상 분석

    Youngrog Kim, Suyoung Jang, Jun Sung Jang, Dong Hyun Kang, Jin Hyeok Kim

    김영록, 장수영, 장준성, 강동현, 김진혁

    Solar energy has been recognized as an alternative energy source that can help address fuel depletion and climate change issues. As a … + READ MORE
    Solar energy has been recognized as an alternative energy source that can help address fuel depletion and climate change issues. As a renewable energy alternative to fossil fuels, it is an eco-friendly and unlimited energy source. Among solar cells, thin film Cu2ZnSn(S,Se)4 (CZTSSe) is currently being actively studied as an alternative to heavily commercialized Cu(In,Ga)Se2 (CIGS) thin film solar cells, which rely upon costly and scarce indium and gallium. Currently, the highest efficiency achieved by CZTSSe cells is 14.9 %, lower than the CIGS record of 23.35 %. When applied to devices, CZTSSe thin films perform poorly compared to other materials due to problems including lattice defects, conduction band offset, secondary phase information, and narrow stable phase regions, so improving their performance is essential. Research into ways of improving performance by doping with Germanium and Cadmium is underway. Specifically, Ge can be doped into CZTSSe, replacing Sn to reduce pinholes and bulk recombination. Additionally, partially replacing Zn with Cd can facilitate grain growth and suppress secondary phase formation. In this study, we analyzed the device’s performance after doping Ge into CZTSSe thin film using evaporation, and doping Cd using chemical bath deposition. The Ge doped thin film showed a larger bandgap than the undoped reference thin film, achieving the highest Voc of 494 mV in the device. The Cd doped thin film showed a smaller bandgap than the undoped reference thin film, with the highest Jsc of 36.9 mA/cm2. As a result, the thin film solar cells achieved a power conversion efficiency of 10.84 %, representing a 20 % improvement in power conversion efficiency compared to the undoped reference device. - COLLAPSE
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    27 October 2024

  • Research Paper

    Curing Effect on the Mechanical Properties of Ag Nanowire/UV Curable Polymer (NOA 68) Nanocomposites

    UV 경화 폴리머(NOA 68)/은 나노와이어 복합재료의 기계적 특성 분석

    Yeojin Kang, Dongjoo Kang, Won Jung Park, Jong-Man Kim, Dongyun Lee

    강여진, 강동주, 박원정, 김종만, 이동윤

    In this study, a composite material suitable for flexible transparent electrodes was fabricated using Norland Optical Adhesive 68 (NOA 68), an ultraviolet … + READ MORE
    In this study, a composite material suitable for flexible transparent electrodes was fabricated using Norland Optical Adhesive 68 (NOA 68), an ultraviolet (UV) curable polymer, and silver nanowires (Ag nanowire, AgNW). The mechanical behavior of this composite was then analyzed. A AgNW network structure was embedded in the NOA 68 polymer and cured using UV energy. The composite was prepared with an AgNW network structure formed approximately 4 µm from the top of the NOA 68 matrix. Tensile test specimens were prepared according to ASTM standards, and tensile tests were conducted at room temperature in air. Scanning electron microscopy (SEM) and tensile tests were used to analyze the changes in mechanical behavior according to UV exposure time and the presence of AgNW. The results showed that as UV curing time increased, the yield strength of the composite increased while the elongation decreased. Regardless of the presence of the AgNW filler, the stress-strain curves of the ductile polymer exhibited the typical mechanical behavior of semi-crystalline polymers as UV curing time increased, characterized by strain softening. It was also confirmed that the composite impregnated with AgNW exhibited higher strength in response to changes in mechanical properties due to UV curing. - COLLAPSE
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    27 October 2024
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