• 한국세라믹학회지
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• 제43권1호
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• pp.10-15
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• 2006

Photoluminescence (PL) and crystal structures of the $(l-x)CaWO_4-xLi_2WO_4$ binary system added with $Eu_2O_3$ activator have been characterized. The $CaWO_4\;and\;Li_2WO_4$ have the scheelite and phenakite structures respectively. The $CaWO_4-Li_2WO_4-Eu_2O_3$ phosphors show the red luminescence of 613 nm peak wavelength. The wavelength range of excitation spectral band is $380\~470$ nm with the peak wavelength of 397 nm. The $0.88(0.5CaWO_4-0.5Li_2WO_4)-0.12Eu_2O_3$ showed the most superior luminescence characteristics. The effect of co-doping elements such as $Al_2O_3$ and rare-earth oxides on PL has been characterized. The co-doping elements deteriorated the luminescence intensity except the $Al_2O_3$ and $Gd_2O_3$. The PL characteristics of $CaWO_4-Li_2WO_4-Eu_2O_3$ phosphors have been compared to those of the alkali europium double molybdates (tungstates) of scheelite-related structure such as $LiEu(MoO_4)_2$ and $CsEu(MoO_4)_2$. The crystal structures of $(l-y)[(l-x)CaWO_4-xLi_2WO_4]-yEu_2O_3$ phosphors have been characterized using XRD data and rietveld refinement.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2007년도 7th International Meeting on Information Display 제7권2호
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• pp.1388-1390
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• 2007

This paper investigates how various concentrations of lithium ion influence on crystallization of MgO in thin films formed by spin coating and an the discharge characteristic in a flat fluorescent lamp structure. The XRD results indicate $Li^+$ ion enhances the growth of MgO crystal in a spin coated thin film. The discharge property with the $Li^+$ ion doped MgO films show the lithium ion in MgO film clearly reduce the initial discharge voltages of test devices. Interestingly, the test panels with various doped MgO film have somewhat higher static memory margin of than that of pure-MgO owing probably to the pore structure of spin coated MgO films. The CL spectra, which confirm that the doping creates defects energy levels in the band gap of MgO, show the $F^+$ center is the main defects in doped MgO films.

• 분석과학
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• 제8권4호
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• pp.583-590
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• 1995

Pitch-based mesophase carbon fibers prepared at different temperatures were heat-treated at temperatures lower than those of the preparation and the electrochemical Li doping/undoping characteristics were evaluated in relation to the data of IR, mass, etc. Presence of surface hydroxyls were confirmed by FTIR for lower temperature sample which showed poor anode characteristics. Upon oxidative heating, removal of surface hydroxyls took place, resulting in a remarkable improvement of the electrode characteristics. At the same time, surface roughening took place, which was confirmed by SEM and double layer capacity measurements. In situ mass spectra obesrved during the heat-treatments showed gas evolution of $H_2O$, CO, $CO_2$, $C_2H_4$, and/or $H_2$ depending on the conditions. These data together with those of weight loss and conductivity provided us a valuable information in regard to the evaluation of the electrochemical characteristics.

• Applied Science and Convergence Technology
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• 제23권2호
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• pp.72-82
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• 2014

Lithium-ion batteries (LIBs) have become popular electrochemical devices. Due to the unique advantages of LIBs in terms of high operating voltage, high energy density, low self-discharge, and absence of memory effects, their application range, which was primarily restricted to portable electronic devices, is now being extended to high-power applications, such as electric vehicles (EVs) and hybrid electrical vehicles (HEVs). Among various anode materials, $Li_4Ti_5O_{12}$ (LTO) is believed to be a promising anode material for high-power LIBs due to its advantages of high working potential and outstanding cyclic stability. However, the rate performance of LTO is limited by its intrinsically low electronic conductivity and poor $Li^+$ ion diffusion coefficient. This review highlights the recent progress in improving the rate performance of LTO through doping, compositing, and nanostructuring strategies.

• Journal of Magnetics
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• 제20권2호
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• pp.97-102
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• 2015

The waste of sintered Nd-Fe-B magnets was recycled using the method of dopingPrNd nanoparticles. The effect of PrNd nanoparticle doping on the magnetic properties of the regenerated magnets has been studied. As the content of the PrNd nanoparticles increases, the coercivity increases monotonically, whereas both the remanence and the maximum energy products reach the maximum values for 4 wt% PrNd doping. Microstructural observation reveals that the appropriate addition of PrNd nanoparticles improves the magnetic properties and refines the grain. Domain investigation shows that the self-pinning effect of the rare earth (Re)-rich phase is enhanced by PrNd nano-particle doping. Compared to the magnet with 4 wt% PrNd alloy prepared using the dual-alloy method, the regenerated magnet doped with the same number of PrNd nanoparticles exhibits better magnetic properties and a more homogeneous microstructure. Therefore, it is concluded that PrNd nanoparticle doping is an efficient method for recycling the leftover scraps of Nd-Fe-B magnets.

• Macromolecular Research
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• 제8권3호
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• pp.116-119
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• 2000

The doping behaviors of water-soluble poly(3-thiopheneacetic acid) (P3TAA) and ie gel using I$_2$and concentrated HCIO$_4$aqueous solutions were investigated by UV-Visible absorption spectrometer. Electrical conductivity of tile doped polyhiophene gel was also studied. I$_2$-doping of water-soluble P3TAA gave rise to a new broad polaron peak at around 749 nm, which corresponds to localization of electron. It was found that doping ability of P3TAA gel was strikingly dependent on the concentration of HCIQ solution.

• 전기화학회지
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• 제14권1호
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• pp.33-37
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• 2011

$Li_4Ti_5O_{12}$는 우수한 안정성으로 고출력 배터리의 음극 물질로 주 목 받고 있다. 그러나 절연체로서 전도도의 개선이 필요한 상황으로 다양한 방법이 시도되고 있다. 본 연구에서는 Cr 도핑을 통해서 $Li_4Ti_5O_{12}$의 전도도 향상을 목표로 하였으며, X-선 흡수 실험 및 FEFF 8.4 코드를 이용한 제일원리 계산을 통해서 도핑에 의한 미세 구조 및 전자 구조의 변화를 분석하였다. Cr 도핑은 페르미 레벨을 Cr d 밴드의 중심에 위치시켜 전도성을향상시켰으며, Ti d 밴드의 전자밀도를 높여 XANES pre-edge및 White line의 변화를 야기했다.

• 한국분말재료학회지
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• 제30권6호
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• pp.516-520
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• 2023

Highly safe lithium-ion batteries (LIBs) are required for large-scale applications such as electrical vehicles and energy storage systems. A highly stable cathode is essential for the development of safe LIBs. LiFePO₄ is one of the most stable cathodes because of its stable structure and strong bonding between P and O. However, it has a lower energy density than lithium transition metal oxides. To investigate the high energy density of phosphate materials, vanadium phosphates were investigated. Vanadium enables multiple redox reactions as well as high redox potentials. LiVPO₄O has two redox reactions (V⁵⁺/V⁴⁺/V³⁺) but low electrochemical activity. In this study, LiVPO₄O is doped with fluorine to improve its electrochemical activity and increase its operational redox potential. With increasing fluorine content in LiVPO₄O_1-xF_x, the local vanadium structure changed as the vanadium oxidation state changed. In addition, the operating potential increased with increasing fluorine content. Thus, it was confirmed that fluorine doping leads to a strong inductive effect and high operating voltage, which helps improve the energy density of the cathode materials.

• 한국재료학회지
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• 제20권12호
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• pp.669-675
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• 2010

One of the greatest challenges for our society is providing powerful electrochemical energy conversion and storage devices. Rechargeable lithium-ion batteries and fuel cells are among the most promising candidates in terms of energy and power density. As the starting material, $TiCl_4{\cdot}YCl_3$ solution and dispersing agent (HCP) were mixed and synthesized using ammonia as the precipitation agent, in order to prepare the nano size Y doped spherical $TiO_2$ precursor. Then, the $Li_4Ti_5O_{12}$ was synthesized using solid state reaction method through the stoichiometric mixture of Y doped spherical $TiO_2$ precursor and LiOH. The Ti mole increased the concentration of the spherical particle size due to the addition of HPC with a similar particle size distribution in a well in which $Li_4Ti_5O_{12}$ spherical particles could be obtained. The optimal synthesis conditions and the molar ratio of the Ti 0.05 mol reaction at $50^{\circ}C$ for 30 minutes and at $850^{\circ}C$ for 6 hours heat treatment time were optimized. $Li_4Ti_5O_{12}$ was prepared by the above conditions as a working electrode after generating the Coin cell; then, electrochemical properties were evaluated when the voltage range of 1.5V was flat, the initial capacity was 141 mAh/g, and cycle retention rate was 86%; also, redox reactions between 1.5 and 1.7V, which arose from the insertion and deintercalation of 0.005 mole of Y doping is not a case of doping because the C-rate characteristics were significantly better.

• Bulletin of the Korean Chemical Society
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• 제34권7호
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• pp.2029-2035
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• 2013

The impact of phosphorous (P)-doping on the electrochemical performance and surface chemistry of soft carbon is investigated by means of galvanostatic cycling and ex situ X-ray photoelectron spectroscopy (XPS). P-doping plays an important role in storing more Li ions and discernibly improves reversible capacity. However, the discharge capacity retention of P-doped soft carbon electrodes deteriorated at $60^{\circ}C$ compared to non-doped soft carbon. This poor capacity retention could be improved by vinylene carbonate (VC) participating in forming a protective interfacial chemistry on soft carbon. In addition, the effect of P-doping on exothermic thermal reactions of lithiated soft carbon with electrolyte solution is discussed on the basis of differential scanning calorimetry (DSC) results.