• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.799-801
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• 1988

This paper was studied on the effects of Ca-La-Nb substitution and Zr/Ti ratio variation to Pb(Zr, Ti)$O_3$ system on structural, electrical, optical and sound level characteristics in order to develope the piezoelectric and electrooptic ceramic devices. Also the specimens were prepared by the two stage sintering technique. The molecular formular was X($CaO{\cdot}1/4La_{2}O_{3}{\cdot}1/4Nb_{2}O_{5}){\cdot}(1-X)Pb(Zr_{Y}Ti_{1-Y})O_{3}$(x=100X, y=100Y), and the variation of x was $6{\sim}12$, y was 60${\sim}$49 and second stage sintering time was 20${\sim}$40 hours. The experimental results obtained from this study are as follows : 1. The density was decreased, the grain size was increased according to increase of Ca-La-Nb substitution. 2. The crystal structure was rhombohedral in composition 6/60/40, and the crystal structure was tetragonal and cubic according to increase of Ca-La-Nb substitution. 3. The Ca substitution of PZT system enhanced the sintering property. The Pb site vacancy resulting from the substitution of La-Nb increased the dielectrical constant, the piezoelectric charge constant, the dielectric loss and decreased the coercive field. 4. The resistivity of PZT system which has the P type conduction mechanism increased according to substitution of La-Nb because of the substituent acting as donor. 5. The PZT ceramics varied from ferroelectric substance according to increase of Ca-La-Nb substituent. The coercive field and saturation remanent polarization decreased, and at last straight line according to increase of La-Nb substitution. 6. The amount of Ca-La-Nb substitution to improve the light transmittance of speciment was 10 mol%, the Zr/Ti ratio was 49/51, and the second stage sintering time was 40 hours. 7. According to Ca-La-Nb substitution, the specimens was to be transparent. The 7.5/51/49 specimen was suitable for transparent sound vibrator because it had 58% light transmittance (thick 0.2[mm], wave length 700[mm]) and 48% electromechanical coupling factor.

• Journal of the Korean Vacuum Society
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• v.9 no.3
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• pp.227-232
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• 2000

$MgTiO_3$thin films have been grown on various substrates by pulsed laser deposition (PLD) to investigate the application for microwave dielectrics and optical devices. Epitaxial $MgTiO_3$thin films were obtained on sapphire (c-plane$A1_2O_3$$MgTiO_3$thin films deposited on $SiO_2/Si$ and platinized silicon ($Pt/Ti/SiO_2/Si$) substrates were highly oriented. $MgTiO_3$thin films grown on sapphire were transparent in the visible and had a sharp absorption edge about 290 nm. These $MgTiO_3$thin films had extremely fine feature of surface morphology, i.e., rms roughness of 0.87 nm, which was examined by AFM. We have investigated the dielectric properties of the $MgTiO_3$thin films in $MIM(Pt/MgTiO_3/Pt)$ capacitors. Dielectric constant and loss of $MgTiO_3$thin films deposited by PLD were about 24 and 1.5% at 1 MHz, respectively. These $MgTiO_3$thin films also exhibited little dielectric dispersion.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.239.1-239.1
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• 2011

Dye sensitized solar cells (DSC) are promising devices for inexpensive, nontoxic, transparent, and large-scale solar energy conversion. Generally thick $TiO_2$ nanoporous films act as efficient photoanodes with their large surface area for absorbing light. However, electron transport through nanoparticle networks causes the slowdown and the loss of electron transport because of a number of interparticle boundaries inside the conduction path. We have studied DSCs with precisely dimension-controlled $TiO_2$ nanotubes array as photoanode. $TiO_2$ nanotubes array is prepared by template-directed fabrication method with atomic layer deposition. Well-ordered nanotubes array provides not only large surface area for light absorbing but also direct pathway for electrons with minimalized grain boundaries. Large enlongated anatase grains in the nanotubes could enhance the conductivity of electrons, but also suppress the recombination with holes through defect sites during diffusion into the electrode. To study the effect of grain boundaries, we fabricated two kinds of nanotubes which have different grain sizes by controlling deposition conditions. And we studied electron conduction through two kinds of nanotubes with different grain structures. The solar cell performance was studied as a function of thickness and grain structures. And overall solar-to-electric energy conversion efficiencies of up to 7% were obtained.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.348-348
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• 2010

Behaviors of $TiO_2$-based photocatalysts with different surface structures on the removal of gas-phase toluene with and without UV irradiation are reported. P-25(Degussa) $TiO_2$ powder dispersed in distilled water by sonication was deposited on the transparent glasses and then dried. Some of the samples were further annealed in oven for 1 hr. These samples obtained before and after annealing were characterized by Brunauer- Emmett-Teller (BET), Transmission Electron Microscope (TEM), X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared (FT-IR) spectrometry, respectively. Based on BET and TEM data, no significant structural change upon annealing could be identified. However, the sample without annealing showed a significantly higher ability for removing toluene both in the presence and absence of the UV light. XPS and FT-IR results clearly revealed that the population of the OH groups on the surface of $TiO_2$ was higher for the sample without annealing, indicating that the OH groups can enhance the adsorption capacity and photocatalytic activity of $TiO_2$ for the removal of the gas-phase toluene.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.6
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• pp.1073-1081
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• 2000

The photo-oxidation of an aqueous humic acid solution using $TiO_2$ sols. which is transparent in visible range, was studied. The $TiO_2$ sols were prepared by a process wherein hydrogen peroxide was added to a gel of $TiO(OH)_2$ originated from hydrolysis of $TiCl_4$, and the resulting titanium peroxo solution(TPS) was heated. The concentration of $TiO_2$ used for photo-oxidation was about 100ppm, determined by comparing the photoluminescence(PL) intensity measured as a function of $TiO_2$ concentration. $TiO_2$ sols aged at $100^{\circ}C$ for more than 12h were found to exhibit a maximum rate in photocatalytic decomposition of humic acid. and the efficiency was better than that of Degussa P25. In addition, the resulting aqueous humic acid after photocatalytic decomposition with sols had an excellent transmittance of visible light, while that treated with Degussa P25 was still turbid. caused by $TiO_2$ particles.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.10
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• pp.609-614
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• 2017

The proposed stretchable transparent electrodes based on silver nanowires (AgNWs) were prepared on a polyurethane (PU) substrate. In order toavoid the surface roughness caused by the silver nanowires, a titanium oxide ($TiO_2$) buffer layer was addedby coating and heating the organometallic sol-gel solution. The fabricated stretchable electrodes showedan electrical sheet resistance of $24{\Omega}sq^{-1}$, 78% transmittance at 550 nm, and an average surface roughness below 5 nm. Furthermore, the AgNW-based electrode maintained its initial electrical resistance under 130% strain testing conditions, without the assistance of additional conductive polymer layers. In this paper, the critical role of the $TiO_2$ buffer layer between the AgNW network and the PU substrate has been discussed.

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.252-258
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• 2002

Transparent $TiO_2$ thin films prepared by sol-gel process using the modification of titanium(IV) alkoxide showed improved thermal stability and high refraction index. Compared to the pure $TiO_2$ film, the modified $TiO_2$ films show the increased index of refraction under proper condition at pH 2.5. Transparency of these $TiO_2$ thin films were more than 80% in the visible region. It has been demonstrated that the reaction occurs in the amorphous phase: an exchange of phase results in anatase before and after 400$^{\circ}C$, in rutile over 700$^{\circ}$C form the XRD results. The particle sizes, shapes and structures of these nanoclusters in the $TiO_2$ films have been identified through a SEM and XRD. The physical properties and structures of their powders have also been studied through a SEM, XRD, TGA and DSC. The thickness and index of refraction have been determined by the analysis of ellipsometric spectra.

• The Korean Journal of Ceramics
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• v.5 no.4
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• pp.341-347
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• 1999

An ambiguity on the correct room temperature structure of $Bi_5Ti_3FeO_{15}$ was resolved using a combined Rietveld refinement of neutron and X-ray diffraction. The structure of this compound has been reported to have a space group of F2mm (adopting 2-fold rotation symmetry along the c-axis) or A21am. However, our diffraction, study reveals that some reflections would violate F-centering and confirm that the belong to $A2_1$am. Out refinement with the space group of $A2_1$am converged at $R_p=6.85%, R_wp=9.23%$ and $\chi^2$=1.66 for an isotropic temperature model with 85 variables. The lattice constants are a=5.4677(1) $\AA$, b=5.4396(1) $\AA$, and c=41.2475(8)$\AA$. In structure, Ti/Fe atoms at the oxygen octahedral sites of the perovskite unit are completely disordered, resulting in that these atoms are transparent in neutron diffraction. The octahedra of the perovskite unit are relatively displaced along the a-axis against the Bi atoms, which contribute as a major component to the spontaneous polarization of $Bi_5Ti_3FeO_{15}$.

• Journal of the Korean Ceramic Society
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• v.31 no.12
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• pp.1423-1428
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• 1994

TiO2 doped sapphire single crystals were grown by Verneuil method. The doping amount of TiO2 to Al2O3 were varied 0.1, 0.2, 0.3 wt% respectively. The grown crystals have reddish color and somewhat transparent. Optimum growth condition was established by changing growth rate and gas flow ratio. Growth condition are as follows; The flow rate range of oxygen ws 5.0~7.3 ι/min and that of hydrogen was 16~25ι/min and average growth rate was 6~8mm/hr. The basic cause of color appearence and defects in crystal were studied.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.26-27
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• 2008

본 연구는 투명전도성전극(TCO)인 ITO를 대체하기 위해 ZnO에 $Al_2O_3$, $SiO_2$, $TiO_2$의 불순물을 도핑하여 박막의 전기적 및 광학적 특성에 관한 연구를 하였다. 불순물 도핑은 2wt.%로 진행 하였고, 동일한 전압과 두께로 그 특성을 비교 하였으며, 특성으로는 UV-Vis를 이용한 광투과율 측정과 광투과율을 이용한 박막의 광학적 밴드갭과 굴절률을 계산 하였다. 전기적 특성으로는 4-Point Probe로 면저항과 비저항값을 측정하였다.