• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.10
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• pp.971-975
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• 2006

[ $SrTiO_3:Al,Pr$ ] red phosphors doped with Y and Er were synthesized by solid state reaction method. The luminescence properties of $SrTiO_3:Al,Pr$ phosphors before and after doping were examined by photoluminescence. Efforts were paid to elucidate the cause of the increase of green luminescence in $(Sr_{0.95}Y_{0.05})TiO_3:Pr,Er\;and\;(Sr_{0.95}Y_{0.05})TiO_3:Pr,Al$ phosphors. The enhanced green luminescence was interpreted by the energy transfer between $Er^{3+}\;and\;Pr^{3+}$ ions, and the change of bandgap in the $(Sr_{0.95}Y_{0.05})TiO_3:Pr$ phosphors.

• Journal of Powder Materials
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• v.18 no.1
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• pp.41-48
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• 2011

As a pore precursor, carbon black with different content of 0 to 60 vol% were added to (Ba,Sr)$TiO_3$ powder. Porous (Ba,Sr)$TiO_3$ ceramics were prepared by pressureless sintering at $1350^{\circ}C$ for 1h under air. Effects of carbon black content on the microstructure and PTCR characteristics of porous (Ba,Sr)$TiO_3$ ceramics were investigated. The porosity of porous (Ba,Sr)$TiO_3$ ceramics increased from 6.97% to 18.22% and the grain size slightly decreased from $7.51\;{\mu}m$ to $5.96\;{\mu}m$ with increasing carbon black contents. PTCR jump of the (Ba,Sr)$TiO_3$ ceramics prepared by adding carbon black was more than $10^5$, and slightly increased with increasing carbon black. The PTCR jump in the (Ba,Sr)$TiO_3$ ceramics prepared by adding 40 vol% carbon black showed an excellent value of $9.68{\times}10^5$, which was above two times higher than that in (Ba,Sr)$TiO_3$ ceramics. These results correspond with Heywang model for the explanation of PTCR effect in (Ba,Sr)$TiO_3$ ceramics. It was considered that carbon black is an effective additive for preparing porous $BaTiO_3$ based ceramics. It is believed that newly prepared (Ba,Sr)$TiO_3$ cermics can be used for PTC thermistor.

• Journal of the Korean institute of surface engineering
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• v.54 no.4
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• pp.178-183
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• 2021

The temperature and frequency dependence of the dielectric constant of the BaTiO₃ substituted with two types of donor dopants, Nb⁵⁺ and Ta⁵⁺, respectively, were compared and analyzed. Dielectric specimens of four specific compositions, Ba_0.95Nb_0.05TiO₃, Ba_0.90Nb_0.10TiO₃, Ba_0.95Ta_0.05TiO₃, and Ba_0.90Ta_0.010TiO₃ were prepared by calcining at 1100 ℃ and sintering at 1300 ℃ to have a perovskite structure to measure capacitance. XRD and SEM analysis were used to observe the structure, with particular focus on the integration into the Nb⁵⁺ and Ta⁵⁺ substituted BaTiO₃ crystal lattice. X-ray diffraction peaks in the (200) and (002) planes were observed between 45.10° and 45.45° of the BaTiO₃ solid solution substituted with different fractions of Nb⁵⁺ and Ta⁵⁺. The dielectric properties were analyzed and the relationship between the properties and structure of the substituted BaTiO₃ was established. The fine particles and high density of the substituted BaTiO₃ were maintained like pure BaTiO₃, and in particular, a shift toward the low temperature side of the phase transition temperature range was clearly found, unlike pure BaTiO₃. In addition, the phase transition at a temperature higher than the Curie temperature relatively satisfies the modified Curie-Weiss law.

• Korean Journal of Materials Research
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• v.10 no.4
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• pp.282-289
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• 2000

$PbTiO_3$ films were fabricated by electron cyclotron resonance plasma enhanced chemical vapor deposition(ECR-PECVD). Deposition characteristics of $PbTiO_3$films on $RuO_2$ and Pt substrates were investigated with varying the flow rate of metalorganic source and substrate temperature. The residence time of Pb-oxide molecules in much longer on $RuO_2$ than on Pt substrate, while the perovskite nucleation is more difficult on $RuO_2$ than on Pt substrate. Therefore, the process conditions to obtain the single perovskite $PbTiO_3$ phase are more restricted on $RuO_2$ than on Pt substrates. An introduction of Ti-oxide seed layer increases perovskite nucleation density and thus enlarges the process window to obtain the single perovkite phase. The introduction of Ti-oxide seed layer make the PZT film that Ti-components of $PbTiO_3$ are partially substituted with Zr atoms have single perovskite phase for the wide range of Zr/(Zr+Ti) concentration ratios.

• Journal of Biomedical Engineering Research
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• v.25 no.5
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• pp.383-389
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• 2004

A commercially pure Ti(CP-Ti) and Ti-25wt％Pd alloy for dental applications were cast into a phosphate-bonded Al$_2$ $O_3$/ $SiO_2$ investment mold and the surface of the casting specimens were investigated by means of SEM/EDS, XRD and XPS. The addition of 25wt％Pd in CP-Ti showed a moderate mold reaction owing to the considerable lowering of melting point. XRD analysis of the investment after burn-out treatment revealed that it consisted essentially of $SiO_2$, Al$_2$ $O_3$, P$_2$O$\_$5/, Mg$_3$(P $O_4$)$_2$, AlP $O_4$, Mg$_2$ $SiO_4$, MgAl$_2$ $O_4$ The mold reaction products were Ti$\_$5/Si$_3$ and Ti $O_2$ in case of CP-Ti casting and Ti $O_2$ and SiO$\_$x/ in case of Ti-25wt％ Pd casting.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.480-483
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• 2001

Epitaxial rutile-$TiO_2$ and anatase-$TiO_2$ films were grown at $800^{\circ}C$ on $Al_2O_3$ (1102) and $LaAlO_3$ (001), respectively, using pulsed laser deposition. The formation of different phases on different substrates could be qualitatively explained by the atomic arrangements at the interfaces. We also successfully deposited epitaxial rutile-$TiO_2$ and anatase-$TiO_2$ films on conductive $RuO_2$ and $La_{0.5}Sr_{0.5}CoO_{3}$ electrodes, respectively. Using a Kelvin probe, we measured the photovoltaic properties of these multilayer structures. A rutile-$TiO_2$ film grown on $RuO_2$ showed a very broad peak in the visible light region. An epitaxial anatase-$TiO_2$ film grown on $La_{0.5}Sr_{0.5}CoO_{3}$ showed a strong peak with a threshold energy of 3.05 eV.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.260-261
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• 2005

The heterolayered thick/thin structure consisting of $Pb(Zr_{0.52}Ti_{0.48})O_3$ and $BaTiO_3(BT)$ were fabricated by a sol-gel process. PZT powders, prepared by the sol-gel method, were mixed with an organic vehicle and the PZT thick films were fabricated by the screen printing techniques on alumina substrate with Pt electrodes. The microstructural and dielectric characteristics of the stacked heterolayered PZT/BT/PZT films were investigated by varying the number of coating $BaTiO_3$ layers. The existence of a $BaTiO_3$ layer between the PZT thick films of the tri-layer $Pb(Zr_xTi_{1-x})O_3/BaTiO_3/Pb(Zr_xTi_{1-x})O_3$thick/thin/thick film can greatly improve the leakage current properties of the PZT thick films. The average thickness of a PZT(5248)/$BaTiO_3$ heterolayered thick/thin film was 25$\mu$m. The relative dielectric constant and dielectric loss of the PZT(5248)/$BaTiO_3$-3 heterolayered thin film coated three times were 1087 and 1.00% at 1[MHz].

• Korean Chemical Engineering Research
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• v.45 no.5
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• pp.448-454
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• 2007

Hydrothermal synthesis was conducted with starting material as Barium hydroxide and hydrous titania ($TiO_2{\cdot}xH_2O$) to obtain barium titanate fine Powder. The conversion, crystal structure and properties of as-prepared powder were investigated according to reaction temperature, time and concentration. The effect of variables on conversion was in order of time < temperature < concentration and the maximum conversion reached to 99.5% in the case of hydrothermal synthesis at $180^{\circ}C$ for 2 h with 2.0 M reactant concentration. At low concentration such as 0.25 M, formation of unreacted $BaCO_3$ and $TiO_2$ was not inevitable at even high reaction temperature and these components converted into $BaTi_2O_5$ at high temperature and remained as impurity. As concentration of reactant increased, the size of as-synthesized $BaTiO_3$ powder deceased and Ba/Ti molar ratio approached into 1, showing Ba/Ti ratio of $1{\pm}0.005$ for reaction at $180^{\circ}C$ for 2 h with 2.0 M concentration.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.865-868
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• 2000

It was examined that the relationship between microstructures, electrical properties and crystal structure of (1-x)CaMnO$_3$-xCaTiO$_3$solid solution system which was made by mixing a semiconducting material CaMnO$_3$of low resistance and a dielectric material CaTiO$_3$of high resistance with variable ratios (x=0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0). As the CaTiO$_3$increased, the resistance, B constant and lattice constant were increased, but the grain size was decreased. On particular, above 50wt% of CaTiO$_3$, the resistance at 2 5$^{\circ}C$ was rapidly increased due to the correlation in connectivity of the lattices between the conductive Mn$^{+4}$ octahedron and the insulative Ti$^{+4}$ octahedron.ron.

• Applied Chemistry for Engineering
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• v.31 no.1
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• pp.43-48
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• 2020

Fe₂O₃ nanoparticles with the mixed structure of cubic and nanorod were synthesized by precipitation, hydrothermal, sol-gel method, etching process and heat treatment. Fe₂O₃/TiO₂ core-shell (CS) of type Fe₂O₃@TiO₂ composite was fabricated on a 20 nm nanolayer of TiO₂ coated on the surface of Fe₂O₃ nanoparticles. Fe₂O₃/TiO₂ yolk-shell (YS) composite was prepared by chemical etching and heat treatment of Fe₂O₃/TiO₂ CS nanoparticles. Physical properties of Fe₂O₃, Fe₂O₃@TiO₂ CS and Fe₂O₃@TiO₂ YS nanoparticles were characterized by FE-SEM, HR-TEM and X-ray diffraction. The solar reflectance, commission internationale de l'Elcairage (CIE) color coordinate and heat shield temperatures of Fe₂O₃, CS and YS type Fe₂O₃@TiO₂ pigments filled with poly acrylate (PA) paints were investigated by UV-Vis-NIR spectrometer and homemade heat shield temperature measuring device. The Fe₂O₃@TiO₂ YS red pigment filled PA composite exhibited excellent near infrared light reflecting performance and also reduced the heat shield temperature of 13 ℃ than that of Fe₂O₃ filled counterparts.