• Journal of the Korean Magnetics Society
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• v.10 no.4
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• pp.154-158
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• 2000

Crystallographic and magnetic properties of the Co and Ti-doped BaF $e_{12-2x}$ $Co_{x}$ $Ti_{x}$ $O_{19}$(0.0$\leq$x$\leq$1.0) system have been investigated by means of x-ray diffractometry, Mossbauer spectroscopy, and vibrating sample magnetometer. The structure of the system was found to be the magnetoplumbite structure, and the lattice parameter a is nearly constant and c increase as the doped Co-Ti contents increasing. We found that the saturation magnetization nearly unchanged but the coercivity rapidly decreased between x = 0.0 and x = 0.2 with increasing x in BaF $e_{12-2x}$ $Co_{x}$ $Ti_{x}$ $O_{19}$. From the Mossbauer spectra analysis Co-Ti ions prefer 12k, 4 $f_{vi}$ and 2b sites.tes.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.365-366
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• 2005

PZT films are the most intensively investigated because PZT has advantages such as low processing temperature and large remnant values. In this paper, the microstructure and electric properties of $Pb(Zr_x,Ti_{(1-x)})O_3/BaTiO_3$ heterolayered thick films with Zr mole ranging from 30 to 70 % screen printed onto a alumina substrate were studied. $Pb(Zr_x,Ti_{(1-x)})O_3$ and $BaTiO_3$ powders were prepared by the sol-gel method. The $BaTiO_3$ powders were calcined at $700^{\circ}C$ for 2 hours. Structural properties of $Pb(Zr_x,Ti_{(1-x)})O_3/BaTiO_3$ multilayered thick films were investigated. As a result of the X-ray diffraction (XRD) analysis, $Pb(Zr_x,Ti_{(1-x)})O_3/BaTiO_3$ exhibited a perovskite polycrystalline phase without pyrochlore phase or any preferred orientation.

• Journal of Environmental Science International
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• v.17 no.8
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• pp.933-941
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• 2008

The formation of $Co_nTiO_{n+2}$ compounds, i.e., $CoTiO_3$ and $CO_2TiO_4$, in a 5wt% $CoO_x/TiO_2$ catalyst after calcination at different temperatures has been characterized via scanning electron microscopy (SEM), Raman and X-ray photoelectron spectroscopy (XPS) measurements to verify our earlier model associated with $CO_3O_4$ nanoparticles present in the catalyst, and laboratory-synthesized $Co_nTiO_{n+2}$ chemicals have been employed to directly measure their activity profiles for CO oxidation at $100^{\circ}C$. SEM measurements with the synthetic $CoTiO_3$ and $CO_2TiO_4$ gave the respective tetragonal and rhombohedral morphology structures, in good agreement with the earlier XRD results. Weak Raman peaks at 239, 267 and 336 $cm^{-1}$ appeared on 5wt% $CoO_x/TiO_2$ after calcination at $570^{\circ}C$ but not on the catalyst calcined at $450^{\circ}C$, and these peaks were observed for the $Co_nTiO_{n+2}$ compounds, particularly $CoTiO_3$. All samples of the two cobalt titanate possessed O ls XPS spectra comprised of strong peaks at $530.0{\pm}0.1$ eV with a shoulder at a 532.2-eV binding energy. The O ls structure at binding energies near 530.0 eV was shown for a sample of 5 wt% $CoO_x/TiO_2$, irrespective to calcination temperature. The noticeable difference between the catalyst calcined at 450 and $570^{\circ}C$ is the 532.2 eV shoulder which was indicative of the formation of the $Co_nTiO_{n+2}$ compounds in the catalyst. No long-life activity maintenance of the synthetic $Co_nTiO_{n+2}$ compounds for CO oxidation at $100^{\circ}C$ was a good vehicle to strongly sup port the reason why the supported $CoO_x$ catalyst after calcination at $570^{\circ}C$ had been practically inactive for the oxidation reaction in our previous study; consequently, the earlier proposed model for the $CO_3O_4$ nanoparticles existing with the catalyst following calcination at different temperatures is very consistent with the characterization results and activity measurements with the cobalt titanates.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.6
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• pp.410-415
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• 1999

$Ba_{1-x}Sr_xTiO_3$ thin films with various ratio of Sr (X = 0.4, 0.5, 0.6) were grown $Pt/TiN/SiO_2/Si$ subastrate by RF magnetron sputtering deposition. As, Ag, and Cu films were deposited on $Ba_{1-x}Sr_xTiO_3$ thin films as top electrodes by using a thermal evaporator. The electrical properties of $Ba_{1-x}Sr_xTiO_3$ thin films for various compositions were characterized and the physical properties at interface between $Ba_{1-x}Sr_xTiO_3$ thin films and top electrodes were evaluated in terms of the work function difference. At x =0.5, the degradation of capacitance is lower to the other compositions. As negative biasapplied, the specimen with Cu top electrode has board saturation region and low leakage current since work function of Cu is bigger than other electrodes.$ Ba_{0.5}Sr_{0.5}TiO_3$ thin films with Cu top electrode, the dielectric constant was measured to the value of 354 at 1 kHz and the leakage current was obtained to the value of $5.26\times10^{-6}A/cm2$ at the forward bias of 2 V.

• Environmental Engineering Research
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• v.21 no.3
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• pp.291-296
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• 2016

Application of photocatalytic nanoparticles has been recently gaining an increased attention as air purifying material for sustainable urban development. The present work reports the photocatalytic removal of gaseous phase nitrogen oxides ($NO_x$) using $TiO_2$-coated zeolite to be applied as a filter media for the urban green infrastructure such as raingardens. The $TiO_2$-coated zeolite was synthesized by simple wet chemistry method and tested in a continuous-flow photo-reactor for its removal efficiency of $NO_x$ under different conditions of the weight percentage of $TiO_2$ coated on the zeolite, and gas retention time. The removal efficiency of $NO_x$ in general increased as the weight percentage of $TiO_2$ coated on the zeolite increased up to 15-20%. Greater than 90% of $NO_x$ was removed at a retention time of one minute using the $TiO_2$-coated zeolite ($TiO_2$ weight percentage = 20%). Overall, $TiO_2$-coated zeolite showed greater efficiency of $NO_x$ removal compared to $TiO_2$ powder probably by providing additional reaction sites from the porous structure of zeolite. It was presumed that the degradation of $NO_x$ is attributed to both the physical adsorption and photocatalytic oxidation that could simultaneously occur at the catalyst surface.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.131-131
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• 2012

We present our recent temperature-programmed desorption (TPD) study on catalytic reductions of $NO_x$ such as NO, $NO_2$, and $N_2O$ over rutile $TiO_2$(110) surfaces. Our results indicate that $NO_2$/NO readily reacts to give NO/$N_2O$ desorption at the substrate temperature as low as 100 K/70 K. Interestingly, $N_2O$, however, does not dissociate into $N_2$ and $O_{BBO}$ over the oxygen vacancy on the $TiO_2$(110) surface. Successive reduction of NO and $NO_2$ into $N_2O$ and NO, respectively, leaves oxygen atoms on the $TiO_2$(110) surface in a form of $O_{ad}$, which can induce additional reductive channels of NO and $NO_2$ at higher temperatures up to 400 K. During the repeated TPD cycles of $NO_x$, our x-ray photoelectron spectroscopy (XPS) analysis indicates that no N atom accumulates on the $TiO_2$ surface.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.3
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• pp.253-261
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• 2005

Catalytic wet oxidation of ppm levels of trichloroethylene (TCE) in water has been conducted using $TiO_2$-supported cobalt oxides at a given temperature and weight hourly space velocity. 5% $CoO_x/TiO_2$ might be the most promising catalyst for the wet oxidation at $36^{\circ}C$ although it exhibited a transient behavior in time on-stream activity. Not only could the bare support be inactive for the wet decomposition reaction, but no TCE removal also occurred by the process of adsorption on $TiO_2$ surface. The catalytic activity was independent of all particle sizes used, thereby representing no mass transfer limitation in intraparticle diffusion. Characterization of the $CoO_x$ catalyst by acquiring XPS spectra of both fresh and used Co surfaces gave different surface spectral features of each $CoO_x$. Co $2p_{3/2}$ binding energy of Co species exposed predominantly onto the outermost surface of the fresh catalyst appeared at 781.3 eV, which is very similar to the chemical states of $CoTiO_x$ such as $Co_2TiO_4$ and $CoTiO_3$. The spent catalyst possessed a 780.3 eV main peak with a satellite structure at 795.8 eV. Based on XPS spectra of reference Co compound, the TCE-exposed Co surfaces could be assigned to be in the form of mainly $Co_3O_4$. XRD measurements indicated that the phase structure of Co species in 5% $CoO_x/TiO_2$ catalyst even before reaction is quite comparable to the diffraction lines of external $Co_3O_4$ standard. A model structure of $CoO_x$ present on titania surfaces would be $Co_3O_4$, encapsulated in thin-film $CoTiO_x$ species consisting of $Co_2TiO_4$ and $CoTiO_3$, which may be active for the decomposition of TCE in a flow of water.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.8
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• pp.474-478
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• 2017

We report on thin-film transistors based on $TiO_x$ pre-annealed by femtosecond laser pulses. A 30-nm thick $TiO_x$ active channel layer was initially deposited by an ALD system. The $TiO_x$ semiconducting films were annealed by irradiation with a femtosecond laser (power: $3W/cm^2$) for 5, 25, and 50s. Atomic force microscopy images revealed that the surface of a $TiO_x$ film without femtosecond laser pre-annealing was relatively rough, while after annealing with femtosecond laser pulses, the surface of the $TiO_x$ films became smooth. With increasing radiation time, the surrounding gas atmosphere could have a larger impact on the $TiO_x$ surface; meanwhile, the thin-film roughness decreased. Thin-film transistors with $TiO_x$ active channels pre-annealed at 50s exhibited good transfer characteristics and an on-to-off current ratio of ${\sim}10^3$.

• Journal of the Korean Ceramic Society
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• v.45 no.5
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• pp.263-267
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• 2008

$(Bi_{1/2}Na_{1/2})TiO_3$-based ceramics have been intensively studied as lead-free piezoelectric ceramics. In this study, the piezoelectric properties and phase transition behaviors of BNT based solid solution $(Bi_{0.5}Na_{0.5})_{1-x}Ca_xTiO_3$ ($X=0.01{\sim}0.25$) were investigated. The morphotropic phase boundary(MPB) zone which BNT is transformed from rhombohedral to cubic structure was appeared by adding $CaTiO_3$ with 0.12 mol by the measurement of permittivity and X-ray diffraction. The behavior which ferroelectric BNT with adding $CaTiO_3$ was changed to antiferroelectric and paraelectric state was confirmed by the measurement ofhysterisis loop and depolarization temperature as a function of temperature. As $CaTiO_3$ concentration was increased, the phase transition temperature was decreased. The piezoelectric properties were highest at 0.01 mol of $CaTiO_3$ concentration. The electromechanical coupling factor($K_t$) and mechanical quality factor($Q_m$) were 42% and 254, respectively.

• Journal of Electrical Engineering and Technology
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• v.2 no.1
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• pp.98-101
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• 2007

Yttrium(Y)-substituted bismuth titanate $(Bi_{4-x},Y_x)Ti_3O_{12}$ [x=0, 0.25, 0.5, 0.75, 1](BYT) thin films were deposited using an RF sputtering method on the $Pt/TiO_2/SiO_2/Si$ substrates. The structural properties and electrical properties of yttrium-substituted $(Bi_4-xYx)Ti_3O_{12}$ thin films were analyzed. The remanent polarization of $(Bi_4-xYx)Ti_3O_{12}$ films increased with increasing Y-content. The $(Bi_{3.25}Y_{0.75})Ti_3O_{12}$ films fabricated using a top Au electrode showed saturated polarization-electric field(P-E) switching curves with a remanent polarization(Pr) of $8{\mu}C/cm^2$ and coercive field (Ec) of 53 kV/cm at an applied voltage of 7 V. The $(Bi_{3.25}Y_{0.75})Ti_3O_{12}$ films exhibited fatigue-free behavior up to $4.5{\times}10^{11}$ read/write switching cycles at a frequency of 1MHz.