• Korean Journal of Materials Research
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• v.20 no.12
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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.

• Journal of the Korean Electrochemical Society
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• v.9 no.2
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• pp.64-69
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• 2006

Cathode materials of Al-doped $Li(Ni_{1/3}Co_{1/3}Mn_{1/3-x}Al_x)O_2$ (x=0.0, 0.005, 0.01 0.05) for lithium ion batteries were synthesized with ultra-sonic spray pyrolysis method and single-step heat treatment. No secondary phases were found in all synthesized powders. The intensity ratio of $I_{003}\;to\;I_{104}$, however, slightly decreased and the particle size increased with the Al contents. The cells with bare, 0.5 and 1.0 at% Al-doped powders showed the initial discharge capacities of 182, 180 and $184mAhg^{-1}$ in a voltage range of $3.0\sim4.5V$ at 1C rate, and the capacity retentions of 81, 77 and 78% at the end of 30 cycles, respectively. But in the voltage range of $3.0\sim4.6V$, the Al-doping significantly enhanced the cycle stability. For example, the discharge capacity after 50 cycles was maintained to 70% in the 0.5 at% Al-doped sample compared to only 30% in no doped sample. The improvement of the cycle stability was thought to be due to $Mn^{3+}$ ion decrease as the Al doping from the XPS analysis results.

• Journal of the Korean Ceramic Society
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• v.47 no.6
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• pp.638-642
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• 2010

The spinel material $Li_4Ti_5O_{12}$ has attracted considerable attention as an anode electrode material for many battery applications owing to its light weight and high energy density. However, the real capacity of $Li_4Ti_5O_{12}$ powder as determined by the solid-state method is lower than the ideal capacity. In this study, we investigated the effect of the dopants in M-doped spinel $Ba_xLi_{4-2x}Ti_5O_{12}$(x=0.005, 0.05, 0.1) powders prepared by the solid-state reaction method and used as the anode material in lithiumion batteries. The results confirmed the effect of the Ba and Sr dopants on the powder properties of the spinel $Li_4Ti_5O_{12}$, which exhibited a pure spinel structure without any secondary phase in its XRD pattern. Moreover, the electrochemical properties of the spinel M-LTO materials were investigated using a half cell. The electrochemical data show that cells with anodes made of undoped $Li_4Ti_5O_{12}$ and Ba- and Sr-doped $Li_4Ti_5O_{12}$ have discharge capacities of 97, 130, and 112 mAh/g, respectively, at the first cycle. Moreover, the Ba- and Sr-doped spinel $Li_4Ti_5O_{12}$ demonstrated good properties in the mid-voltage range at 1.55 V, showing stable cyclic voltammogram properties which surpassed those of the same material without Ba or Sr at 1 C after 100 cycles.

• Journal of the Korean Magnetics Society
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• v.2 no.2
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• pp.99-104
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• 1992

The permeability vs. temperature curve, the loss factor and the microstructure of a commercial Mn-Zn ferrites were investigated by X-ray diffractometer, SEM and LCR meter, where the additives, such as $SnO_{2}$ and $GeO_{2}$, were added to the main composition. Their wt% were 0.05, 0.3 and 1.0, respectively. When the content of additives increased, the SPM (Secondary Peak Maximum) of the permeability moved from $80^{\circ}C$ to below the room temperature. This movement, without the significant change of the microstructure, is because Sn and Ge, having the different ionic radius, were soluble in the matrix. There was no variation of the permeability with the frequency up to 100 kHz. And the loss factor showed the maximum value at 10 kHz.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.72-72
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• 2010

Recent development of organic solar cell approaches the level of 8% power conversion efficiency by the introduction of new materials, improved material engineering, and more sophisticated device structures. As for interface engineering, various interlayer materials such as LiF, CaO, NaF, and KF have been utilized between Al electrode and active layer. Those materials lower the work function of cathode and interface barrier, protect the active layer, enhance charge collection efficiency, and induce active layer doping. However, the addition of another step of thin layer deposition could be a little complicated. Thus, on a typical solar cell structure of Al/P3HT:PCBM/PEDOT:PSS/ITO glass, we used Li:Al alloy electrode instead of Al to render a simple process. J-V measurement under dark and light illumination on the polymer solar cell using Li:Al cathode shows the improvement in electric properties such as decrease in leakage current and series resistance, and increase in circuit current density. This effective charge collection and electron transport correspond to lowered energy barrier for electron transport at the interface, which is measured by ultraviolet photoelectron spectroscopy. Indeed, through the measurement of secondary ion mass spectroscopy, the Li atoms turn out to be located mainly at the interface between polymer and Al metal. In addition, the chemical reaction between polymer and metal electrodes are measured by X-ray photoelectron spectroscopy.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.103-103
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• 2011

The epitaxial Cu-doped ZnO and pure ZnO thin films were grown on Al2O3 (0001) substrates by RF sputtering method. The structures and crystallographic orientations were investigated using X-ray diffraction (XRD) and X-ray absorption spectroscopy. From the XRD pattern, it is observed that peak positions shift towards higher $2{\theta}$ value with Cu doping. The ${\omega}$-scan measurements at the (0002) diffraction peak for these samples reveal that the full-widths at half-maxima (FWHMs) are about $0.017-0.019^{\circ}$, which indicate a good c-axis orientation of the Zn1-xCuxO films. From phi-scan, all of the Zn1-xCuxO films were epitaxially grown. EXAFS measurements also demonstrated that Cu incorporated into a Zn-atom position substitutionally. All the results confirmed that copper ion were well incorporated into the ZnO lattices by substituting Zn sites without changing the wurtzite structure and no secondary phase existed in Cu-doped ZnO thin films.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.56-56
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• 2018

Transparent conductive oxides (TCOs) have attracted attention due to their high electrical conductivity and optical transparency in the visible region. Consequently, TCOs have been widely used as electrode materials in various electronic devices such as flat panel displays and solar cells. Previous studies on TCOs focused on their electrical and optical performances; there have been numerous attempts to improve these properties, such as chemical doping and crystallinity enhancement. Recently, due to rapidly increasing demand for flexible electronics, the academic interest in the mechanical stability of materials has come to the fore as a major issue. In particular, long-term stability under bending is a crucial requirement for flexible electrodes; however, research on this feature is still in the nascent stage. Hydrogen-incorporated amorphous In-Sn-O (a-ITO) thin films were fabricated by introducing hydrogen gas during deposition. The hydrogen concentration in the film was determined by secondary ion mass spectrometry and was found to vary from $4.7{\times}10^{20}$ to $8.1{\times}10^{20}cm^{-3}$ with increasing $H_2$ flow rate. The mechanical stability of the a-ITO thin films dramatically improved because of hydrogen incorporation, without any observable degradation in their electrical or optical properties. With increasing hydrogen concentration, the compressive residual stress gradually decreased and the subgap absorption at around 3.1 eV was suppressed. Considering that the residual stress and subgap absorption mainly originated from defects, hydrogen may be a promising candidate for defect passivation in flexible electronics.

• Proceedings of the KIEE Conference
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• 2001.11b
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• pp.106-108
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• 2001

As 3V cathode material, a new doping spinel material, LiMn1.6Se0.4O4 powder with a phase-pure polycrystalline was synthesized by a sol-gel method. In spite of Jahn-teller distortion in 3V region($2.4{\sim}3.5V$), the LiMn1.6Se0.4O4 electrode shows no capacity loss. The material in the 3V region initially delivers a discharge capacity of 100mAh/g which increase with cycling to reach 105mAh/g after 90cycles. And 5V cathode material LiNi0.5-xMxMn1.5O4(M=Cr, V, Fe) compounds have been synthesized by sol-gel method. a series of electroactive spinel compounds, LiNi0.5-xMxMn1.5O4(M=Cr, V, Fe) has been studied by crystallographic and electrochemical methods. The material presents only one plateau at around 4.5 V vs. Li/Li+ with a large discharge capacity of 152mAh/g and fairly good cyclability.

• Journal of Magnetics
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• v.12 no.4
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• pp.144-148
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• 2007

We report on the observation of p-type conductivity and ferromagnetism in diluted magnetic semiconductor $(Zn_{0.97}Mg_{0.01}Mn_{0.02})O:P$ films grown on $SiO_2/Si$ substrates by pulsed laser deposition. The p-type conduction with hole concentration over $10^{18}cm^{-3}$ is obtained by codoping of Mg and P followed by rapid thermal annealing in an $O_2$ atmosphere. Structural and compositional analyses for the p-type $(Zn_{0.97}Mg_{0.01}Mn_{0.02})O:P$ films annealed at $800^{\circ}C$ indicates that highly c-axis oriented homogeneous films were grown without any detectable formation of secondary phases. The films were found to be transparent in the visible range. The magnetic measurements clearly revealed an enhancement of room temperature ferromagnetism by p-type doping.

• Journal of the Korean Ceramic Society
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• v.56 no.5
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• pp.474-482
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• 2019

Chromium-doped zinc ferrite nanoparticles with the general formula Cr_yZnFe_2-yO₄ (y = 0, 0.025, 0.05, 0.075, and 0.1) were synthesized by a surfactant-assisted chemical co-precipitation route using metal nitrate salt precursors. The phase purity and structural parameters were determined by powder X-ray diffraction. The concentration of Cr³⁺ doped into ZnFe₂O₄ (ZF) noticeably affected the crystallite size, which was in the range of 22 nm to 36 nm, and all samples showed a single cubic spinel structure without any secondary phase or impurities. The lattice parameter, X-ray density, and skeletal density increased with an increase in the Cr-doping concentration; on the other hand, a decreasing trend was observed for the particle size and porosity. The influence of Cr³⁺ substitution on ZF magnetic properties were studied under an applied field of 15 kOe. The overall results revealed that the incorporation of a small amount of Cr dopant changed the structural, electrical, and magnetic properties of ZF.