• Journal of the Korean Ceramic Society
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• v.39 no.11
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• pp.1108-1112
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• 2002

pellets were fabricated as a reactor control material by the powder process. Sinterability of $Dy_2O_3+TiO_2$ mixtures and phases of solid solutions were analyzed by using TMA and XRD, respectively. The thermal conductivity of pellet was determined from the measurement data of the specific heat and the thermal diffusivity of the pellet. The sinterability and the sintered density varied as a function of Dy content in $Dy_xTi_yO_z$. The pellet of $3\;g\;Dy/cm^3\;Dy_xTi_yO_z$ melted in the sintering temperature of $1580{\circ}C$. There were two phases of $Dy_2TiO_5+Dy_2Ti_2O_7$ and a single phase of $Dy_2TiO_5$ for the pellet that has the Dy content of and , respectively. The thermal conductivity of $Dy_xTi_yO_z$ was nearly constant in the temperature range of $25~600{\circ}$. It was 1.69~1.78 W/mK for the pellet sintered in and 1.49~1.55 W/mK for the pellet sintered in $1550{\circ}$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.9
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• pp.825-828
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• 2008

$Sr_xBa_{(1-x)}TiO_3$ red phosphors doped with Pr(0.13 mol%) and Al(O.23 mol%) were synthesized by solid state reaction method. Orthorhombic perovskite structure with increasing value of x in $Sr_xBa_{(1-x)}TiO_3$:Pr,Al phosphors changed to cubic perovskite structure. Emission bands at 615 nm and 492 nm in $Sr_{0.25}Ba_{0.75}TiO_3$:Pr,Al and $BaTiO_3$:Pr,Al phosphors were observed at room temperature. The main cause of green luminescence at 492 nm was explained by the change of the 4f5d band.

• Journal of the Korean Ceramic Society
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• v.38 no.6
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• pp.558-567
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• 2001

본 연구에서는 알콕사이드를 전구물질로 하는 졸겔공정을 이용하여 Bi 과잉 12 mol%의 조성인 B $i_4$ $Ti_3$ $O_{12}$ 박막과 B $i_4$ $Ti_{3-x}$T $a_{x}$ $O_{12}$(x=0.1, 0.2, 0.3) 박막을 제조하였다. XPS 분석에 따르면 Ta 치환 x=0.2에서 Bi 4f의 photoemission 곡선이 낮은 결합에너지로 이동하였고 피크 강도가 감소하는 현상이 관측되었다. 이는 x=0.1과 0.2 사이에서 Bi-O 결합이 길어져 인장상태 하에 있었음을 나타내었다. B $i_4$ $Ti_3$ $O_{12}$(BIT) 박막의 유전상수와 유전손실은 100 kHz에서 340, 0.05이었고, B $i_4$ $Ti_{3-x}$T $a_{x}$ $O_{12}$ 박막에서 이들 값은 x=0.1에서 가장 높았으며, 각각 480, 0.13이었다. B $i_4$ $Ti_3$ $O_{12}$ 박막의 잔류분극과 항전계는 1.24$\mu$C/$ extrm{cm}^2$, 31.4 kV/cm 이었으나, Ta 치환 x=0.2에서 이들 값은 각각 19.7$\mu$C/$\textrm{cm}^2$, 49.5 kV/cm 에 이르렀다. 또한, B $i_4$ $Ti_3$ $O_{12}$ 박막의 누설전류 밀도는 ~$10^{-6}$ A/$\textrm{cm}^2$ 정도이었으며, Ta 치환은 누설전류를 감소시켜 Ta 치환 x=0.2 이상에서 BIT 박막에 비해 한 차수 정도 낮아졌다. Ta 치환에 따른 B $i_4$ $Ti_3$ $O_{12}$ 전기 물성에서 변화는 Bi-O 결합에서 관측된 인장상태로의 전이와 연관성이 있었으며, 덧붙여 치환에서 생성된 전자에 의한 정공보상이 이에 영향을 끼쳤다. 정공보상이 이에 영향을 끼쳤다.끼쳤다.

• Bulletin of the Korean Chemical Society
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• v.22 no.3
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• pp.298-302
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• 2001

A site preference of niobium atom in Rb2-xLa2Ti3-xNbxO10 (0.0 $\leq$ x $\leq1.0)$ and RbLa2-xCaxTi2-xNb1+xO10 (0.0 $\leq$ x $\leq2.0)$, which are the solid-solutions between Rb2La2Ti3O10 and RbCa2Nb3O10, has been investigated by Raman spectroscopy. The Raman spectra of Rb2-xLa2Ti3-xNbxO10 (0.0 $\leq$ x $\leq1.0)$ gave an evidence that niobium atoms substituted for titanium atoms preferably occupy the highly distorted outer octahedral sites rather than the central ones in triple-octahedral perovskite layers. In contrast, the Raman spectra of RbLa2-xCaxTi2-xNb1+xO10 (0.0 $\leq$ x $\leq2.0)$ showed no clear information for the cationic arrangement in perovskite slabs. This difference indicated that a site preference of niobium atoms is observed only when the linear Rb-O-Ti linkage can be replaced by much stronger terminal Nb-O bond with double bond character. From comparison with the Raman spectroscopic behavior of CsLa2-xA’xTi2-xNb1+xO10 (A’ = Ca and Ba; 0.0 $\leqx\leq2.0)$, it is also proposed that a local difference in arrangement of interlayer atoms causes a significantly different solid acidity and photocatalytic activity of the layered perovskite oxides, despite their crystallographically similar structures.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.5
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• pp.397-403
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• 2003

Microwave dielectric properties of (1-x)ZnW $O_4$-xTi $O_2$ ceramic systems were investigated with calcination temperatures and Ti $O_2$ contents. The ZnW $O_4$ ceramic could be suitably sintered at 1075$^{\circ}C$ and showed the dielectric constant of 13.6, quality factor(Q$\times$ $f_{O}$value) of 22,000 and temperature coefficient of resonant frequency($\tau$$_{f}$) of -65$\pm$2ppm/$^{\circ}C$. Increasing the amount of Ti $O_2$ in the range of 0.25 to 0.45 mol, the dielectric constant and $\tau$$_{f}$ increased due to the role of Ti $O_2$ but the quality factor decreased due to the increase of phase boundaries. The 0.7ZnW $O_4$-0.3Ti $O_2$ ceramic showed the dielectric constant of 19.8, qualify factor(Q$\times$ $f_{0}$) of 20,000 and $\tau$$_{f}$ of -3$\pm$1ppm/$^{\circ}C$.>.EX>.>.>.

• Bulletin of the Korean Chemical Society
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• v.32 no.1
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• pp.95-99
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• 2011

$CaTi_{1-x}Fe_xO_3(0{\leq}x{\leq}0.4)$ solid solution photocatalysts were synthesized by iron doping during the conventional solid state reaction at $1100^{\circ}C$ for 5 h and characterized by ultraviolet-visible (UV-vis) absorption spectroscopy, X-ray diffraction, morphological analysis. We found that $CaTi_{1-x}Fe_xO_3$ samples not only absorb UV but also the visible light photons. This is because the Fe substitution at Ti-site in $CaTi_{1-x}Fe_xO_3$ lattice induces the band transition from Fe3d to the Fe3d + Ti3d hybrid orbital. The photocatalytic activity of Fe doped $CaTiO_3$ samples for hydrogen production under UV light irradiation decreased with the increase in the Fe concentration. There exists an optimized concentration of iron in $CaTiO_3$, which yields a maximum photocatalytic activity under visible light ($\lambda\geq420nm$) photons.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.430-433
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• 2001

The $0.96MgTiO_{3}-0.04SrTiO_{3}+xCe(x=0{\sim}1.6wt%)$ ceramics were fabricated by the conventional mixed oxide method. The sintering temperature and time were $1300^{\circ}C$, 2hr., respectively. From the X-ray diffraction patterns, it was found that the perovskite $SrTiO_{3}$ and ilmenite $MgTiO_{3}$ structures were coexisted in the $0.96MgTiO_{3}-0.04SrTiO_{3}+xCe(x=0{\sim}1.6wt%)$ ceramics. The dielectric constant$(\varepsilon_{r})$ was increased with addition of Ce. The temperature coefficient of resonant frequency$(\Gamma_{f})$ was gradually varied from positive value to the negative value with increasing the Ce. The temperature coefficient of resonant frequency of the $0.96MgTiO_{3}-0.04SrTiO_{3}+0.2Ce$ ceramics was near zero, where the dielectric constant, quality factor, and $\Gamma_{f}$ were 20.68, 50,272 and ${-0.5ppm/^{\circ}C}$, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.430-433
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• 2001

The 0.96MgTiO$_3$-0.04SrTiO$_3$+xCe(x=0∼1.6 wt%) ceramics were fabricated by the conventional mixed oxide method. The sintering temperature and time were 1300$^{\circ}C$, 2hr., respectively. From the X-ray diffraction patterns, it was found that the perovskite SrTiO$_3$ and ilmenite MgTiO$_3$ structures were coexisted in the 0.96MgTiO$_3$-0.04SrTiO$_3$+xCe(x=0∼1.6 wt%) ceramics. The dielectric constant($\varepsilon$$\sub$r/) was increased with addition of Ce. The temperature coefficient of resonant frequency($\tau$$\sub$f/) was gradually varied from positive value to the negative value with increasing the Ce. The temperature coefficient of resonant frequency of the 0.96MgTiO$_3$-0.04SrTiO$_3$+0.2Ce ceramics was near zero, where the dielectric constant, quality factor, and $\tau$$\sub$f/ were 20.68, 50, 272 and -0.5pm/$^{\circ}C$, respectively.

• Journal of Korean Ophthalmic Optics Society
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• v.2 no.1
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• pp.9-16
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• 1997

Ferroelectric $Pb_5Ge_{3-x}Ti_xO_{11}$(x=0, 0.015, 0.021, 0.03) single crystals were obtained from the melt by the Czochralski method. Grown crystals were pale brownish yellow and fully transparent. The dielectric relaxation of the $Pb_5Ge_{3-x}Ti_xO_{11}$ single crystals has been studied in the frequency range from 100 Hz to 10 MHz between $20^{\circ}C$ and $600^{\circ}C$. From the results of the these measurements. the temperature of the permittivity maximum was shifted to low temperature with increasing Ti content and the permittivity maximum decreased with increasing Ti content. The frequency dependent dielectric response of $Pb_5Ge_{3-x}Ti_xO_{11}$ single crystals exhibits a Debye type relaxation, with a distribution of relaxation times. Dielectric behavior is characteristic of carrier-dominated response.

• Journal of the Korean Ceramic Society
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• v.40 no.2
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• pp.178-183
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• 2003

Electrical conductivity of$50Li_2O-xTiO_2-(50-x)P_2O_5$ glasses has been studied with an increase of the intermediate$TiO_2$content. Thermal properties were observed from TG-DTA measurement and the variation of glass structure was investigated by FT-IR. The density and glass transition temperature increased with an increase of the $TiO_2$ content. These results were attributed to the fact that bond strengthening was occurred because of the formation of P-O-Ti cross linkages in the glass. The ionic conductivity increased with $TiO_2$ content and a maximum value, $1.2{imes}10^{-6}$S/cm showed at x=20. The ionic conductivity showed a large increasement as a result that the pyrophosphate group become the predominant structural unit. This result can explain that Li ions mobility increased as a number of non-bridging oxygen on phosphate units increased.