• Korean Journal of Materials Research
• /
• v.11 no.8
• /
• pp.363-363
• /
• 2001

In order to improve the optical Performance of green emitting phosphor for plasma display panel (PDP) application, the wet chemical method for preparing $Zn_{2-x}$ $SiO_4$:xMn (xi=0.02. 0.08) phosphor was designed. The spherical phosphor particles were obtained and the size can be between 0.5$\mu\textrm{m}$ and 2$\mu\textrm{m}$. The formation of phosphor, which had the willemite structure, was completed at relatively low temperature of 108$0^{\circ}C$. Also, photoluminescence Properties of the phosphors prepared were investigated under vacuum ultraviolet excitation. In particular, the emission intensity of Zn$_2$SiO$_4$:0.08Mn phosphor having the 1$\mu\textrm{m}$ of particle size was higher than that of commercial phosphor by 40%. The decay time of zinc silicate powder prepared as containing 8 mole% of manganese has been measured as 7.8ms.

• Journal of the Korean Ceramic Society
• /
• v.34 no.1
• /
• pp.109-113
• /
• 1997

When the intensity of X-rays scattered from amorphous materials (very weakly absorbing materials) is measured using standard diffractometric technique, the intensity caused by multiple scattering is obtained in the measured X-ray intensity. Computer programs have been developed to estimate the intensity of the mul-tiple scattering obtained in vitreous SiO2 and B2O3 with various X-rays. Using the above computer program, the intensity ratios of multiple scattering to single scattering in vitreous SiO2 were 0.10~0.16% at CuK$\alpha$, 0.98~5.87% at MoK$\alpha$, and 1.88~17.86% at AgK$\alpha$ in the range of 2$\theta$=0~180$^{\circ}$. Therefore, pri-or to the structural analysis of vitreous SiO2 and B2O3 performed experimentally using X-ray diffractometric technique, the intensity data measured in MoK$\alpha$ and AgK$\alpha$ radiations must be corrected for multiple scattering effect.

• Journal of the Korean Chemical Society
• /
• v.40 no.6
• /
• pp.427-435
• /
• 1996

The structures of fully dehydrated $Ca^{2+}$- and $Cs^+$-exchanged zeolite X, $Ca_{35}Cs_{22}Si_{100}Al_{92}O_{384}$($Ca_{35}Cs_{22}$-X; a=25.071(1) $\AA)$ and $Ca_{29}Cs_{34}Si_{100}Al_{92}O_{384}$($Ca_{29}Cs_{34}$-X; a=24.949(1) $\AA)$, have been determined by single-crystal X-ray diffraction methods in the cubic space group Fd3 at $21(1)^{\circ}C.$ Their structures were refined to the final error indices $R_1$=0.051 and $R_2$=0.044 with 322 reflections for $Ca_{35}Cs_{22}$-X, and $R_1$=0.058 and $R_2$=0.055 with 260 reflections for $Ca_{29}Cs_{34}$-X; $I>3\sigma(I).$ In both structures, $Ca^{2+}$ and $Cs^+$ ions are located at five different crystallographic sites. In dehydrated $Ca_{35}Cs_{22}$-X, sixteen $Ca^{2+}$ ions fill site I, at the centers of the double 6-rings(Ca-O=2.41(1) $\AA$ and $O-Ca-O=93.4(3)^{\circ}).$ Another nineteen $Ca^{2+}$ ions occupy site II (Ca-O=2.29(1) $\AA$, O-Ca-O=118.7(4)') and ten $Cs^+$ ions occupy site II opposite single six-rings in the supercage; each is $1.95\AA$ from the plane of three oxygens (Cs-O=2.99(1) and $O-Cs-O=82.3(3)^{\circ}).$ About three $Cs^+$ ions are found at site II', 2.27 $\AA$ into sodalite cavity from their three-oxygen plane (Cs-O=3.23(1) $\AA$ and $O-Cs-O=75.2(3)^{\circ}).$ The remaining nine $Cs^+$ ions are statistically distributed over site Ⅲ, a 48-fold equipoint in the supercages on twofold axes (Cs-O=3.25(1) $\AA$ and Cs-O=3.49(1) $\AA).$ In dehydrated $Ca_{29}Cs_{34}$-X, sixteen $Ca^{2+}$ ions fill site I(Ca-O=2.38(1) $\AA$ and $O-Ca-O=94.1(4)^{\circ})$ and thirteen $Ca^{2+}$ ions occupy site II (Ca-O=2.32(2) $\AA$, $O-Ca-O=119.7(6)^{\circ}).$ Another twelve $Cs^+$ ions occupy site II; each is $1.93\AA$ from the plane of three oxygens (Cs-O=3.02(1) and $O-Cs-O=83.1(4)^{\circ})$ and seven $Cs^+$ ions occupy site II'; each is $2.22\AA$ into sodalite cavity from their three-oxygen plane (Cs-O=3.21(2) and $O-Cs-O=77.2(4)^{\circ}).$ The remaining sixteen $Cs^+$ ions are found at III site in the supercage (Cs-O=3.11(1) $\AA$ and Cs-O=3.46(2) $\AA).$ It appears that $Ca^{2+}$ ions prefer sites I and II in that order, and that $Cs^+$ ions occupy the remaining sites, except that they are too large to be stable at site I.

• Korean Journal of Materials Research
• /
• v.21 no.8
• /
• pp.439-443
• /
• 2011

The crystal structure and magnetic properties of a new solid solution type ferrite $(Fe_2O_3)_5-(Al_2O_3)_{3.4}-(Ga_2O_3)_{0.6}-SiO$ were investigated using X-ray diffraction and M$\"{o}$ssbauer spectroscopy. The results of the X-ray diffraction pattern indicated that the crystal structure of the sample appears to be a cubic spinel type structure. The lattice constant (a = 8.317 ${\AA}$) decreases slightly with the substitution of $Ga_2O_3$ even though the ionic radii of the Ga ions are larger than that of the Al ions. The results can be attributed to a higher degree of covalency in the Ga-O bonds than in the Al-O and Fe-O bonds, which can also be explained using the observed M$\"{o}$ssbauer parameters, which are the magnetic hyperfine field, isomer shift, and quadrupole splitting. The drastic change in the magnetic structure according to the Ga ion substitution in the $ (Fe_2O_3)_5(Al_2O_3)_{4-x}(Ga_2O_3)_xSiO$ system and the low temperature variation have been studied through a M$\"{o}$ssbauer spectroscopy. The M$\"{o}$ssbauer spectrum at room temperature shows the superpositions of two Zeeman patterns and a strong doublet. It shows significant departures from the prototypical ferrite and is comparable with the diluted ferrite. The doublet of spectrum at room temperature appears to originate from superparamagnetic clusters and also the asymmetry of the doublet appears to be caused by the preferred orientation of the crystallites. The M$\"{o}$ssbauer spectra below room temperature show various complicated patterns, which can be explained by the freezing of the superparamagnetic clusters. On cooling, the magnetic states of the sample were various and multi critical.

• Proceedings of the KIEE Conference
• /
• 1999.11a
• /
• pp.31-34
• /
• 1999

In the present study, we fabricated stoichiometric $(Ba_{1-x}Sr_x)TiO_3$ thin films at various substrate temperature and contents using of magnetron sputtering method on optimized Pt-based electrodes (Pt/TiN/$SiO_2$/Si). The substate temperature deposited at 200[ $^{\circ}C$], 400[$^{\circ}C$] and 600[$^{\circ}C$] and crystalline BST thin films show above 400[$^{\circ}C$]. Also, the composition of $(Ba_{1-x}Sr_x)TiO_3$ thin films deposited on Si wafer substrate at 400[$^{\circ}C$] were closed to stoichiometry($1.015{\sim}1.093$ in A/B ratio), but compositional deviation from a stoichiometry is larger as $SrCO_3$ is added. The drastic decrease of dielectric constant and increase of dielectric loss in $(Ba_{1-x}Sr_x)TiO_3$thin films is observed above 100[kHz]. V-I characteristics of $(Ba_{1-x}Sr_x)TiO_3$ thin films show the decrease of leakage current with the increase of $SrCO_3$ contents.

• Transactions of the Korean hydrogen and new energy society
• /
• v.30 no.2
• /
• pp.128-135
• /
• 2019

In this study, the mesoporous $SiO_2$ (5, 10, or 15 wt%) was incorporated into the polybenzimidazole matrix in order to improve the proton conduction as well as physiochemical properties of composite membrane. The chemical structure of mesoporous $SiO_2$ and crystallinity of as-prepared membranes were analyzed by Fourier-transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD) analysis, respectively. The thermal stability of the pristine $X_1Y_9$ and composite membranes were evaluated by thermogravimetric analyzer (TGA). On other side, the physical and chemical properties of the pristine $X_1Y_9$ and composite membranes were also determined by acid uptake and oxidative stability tests, respectively. With the incorporation of 15 wt% $SiO_2$, the composite membrane exhibits the higher proton conductivity that may be applicable for non-humidified high temperature fuel cell applications.

• Electrical & Electronic Materials
• /
• v.9 no.4
• /
• pp.336-343
• /
• 1996

We have studied the preparation and the properties of $Ba_{1-x}$Sr$_{x}$TiO$_{3}$(BST) thin films by using the sol-gel method. Through the comparison of the effects of various solvents and additives in making solutions, we establish the production method of the stable solution which generates the high quality of BST film. We also set up the heat-treatment conditions for depositing the BST thin film through the TGA and XRD analyses. Through the comparison of the surface conditions of BST films deposited on Pt/Ta/SiO$_{2}$/Si and Pt/Ti/SiO$_{2}$/Si substrates, we find that Ta is more efficient diffusion barrier of Si than Ti so that Ta layer prevents the formation of hillocks. We fabricate the planar type capacitor and measure the dielectric properties of the BST thin film deposited on the Pt/Ta/SiO$_{2}$/Si substrate. Dielectric constant and dielectric loss tangent at 1V, 10kHz, and leakage current density at 3V of the BST thin film are 339, 0.052 and 13.3.mu.A/cm$^{2}$, respectively.ely.

• Journal of the Korean Ceramic Society
• /
• v.43 no.9 s.292
• /
• pp.569-574
• /
• 2006

Transparent glass-ceramics containing fresnoite crystals have been prepared by controlled heat treatment in $K_2O-BaO-TiO_2-SiO_2$ and their nonlinear optical and luminescent properties were investigated using Maker fringe method and Spectrofluorometer. The second harmonic generation was observed in all samples and the values decreased with increasing $K_2O$ content. The luminescence of blue light at ${\sim}482nm$ could be observed and it was shown that the luminescent property was controlled by the $K_2O$ content.

• Korean Chemical Engineering Research
• /
• v.44 no.3
• /
• pp.284-288
• /
• 2006

$(Ca,Sr)_{2-y}MgSi_2O_7:Eu^{2+}{_y}$ (CMS) phosphor particles were prepared by using a spray pyrolysis process. The luminescent property was optimized by changing the content of Eu and the post-treatment temperature. The luminescence characteristics were also monitored with changing the ratio of Ca to Sr. The pure tetragonal $Ca_2MgSi_2O_7$ or $Sr_2MgSi_2O_7$ particles were obtained when the post-treatment temperature was over $1,000^{\circ}C$. The highest emission intensity of CMS particles were achieved when the concentration (y) of Eu and the treatment temperature were 0.05 and $1,250^{\circ}C$,respectively. The emission wavelength $({\lambda}_{max})$ of ${(Ca_{1-x},Sr_x)}_{1.95}MgSi_2O_7:{Eu^{2+}}_{0.05}$ was gradually shifted from 524 nm to 456 nm with increasing the content of Sr due to the reduction of crystal field strength. The emission intensity and its width of $Sr_2MgSi_2O_7:Eu$ was greatly enhanced by substituting Ca of less than 10 mol％ for Sr without any significant peak shift. The morphology of as-prepared particles was spherical, but changed to irregular-shaped one after the post treatment at the temperature range from 900 at $1,300^{\circ}C$.

• Current Photovoltaic Research
• /
• v.5 no.2
• /
• pp.63-67
• /
• 2017

Aluminum oxide ($Al_2O_3$) film deposited by atomic layer deposition (ALD) is known to supply excellent surface passivation properties on crystalline Si surface. The quality of passivation layer is important for high-efficiency silicon solar cell. double-layer structures have many advantages over single-layer materials. $Al_2O_3/SiN_X$ passivation stacks have been widely adopted for high- efficiency silicon solar cells. The first layer, $Al_2O_3$, passivates the surface, while $SiN_X$ acts as a hydrogen source that saturates silicon dangling bonds during annealing treatment. We explored the properties on passivation film of $Al_2O_3/SiN_X$ stack layer with changing the conditions. For the post annealing temperature, it was found that $500^{\circ}C$ is the most suitable temperature to improvement surface passivation.