• ETRI Journal
• /
• v.18 no.1
• /
• pp.15-27
• /
• 1996

The effects of $Nd_2O_3$ and $TiO_2$ addition on the microstructures and microwave dielectic properties of $BaO-Nd_2O_3-TiO_2$ system were investigated. $BaNd_2Ti_4O_{12}$ or $BaNd_2Ti_{5}O_{14}$ phases were observed for compositions based on BaO/$Nd_2O_3$ = 1 ratio. The compositions deviated from $BaO/Nd_2O_3=1$ ratio were composed of major phases of $BaNd_2Ti_4O_{12}$ or $BaNd_2Ti_5O_{14}$, and the compound of $Nd_2O_3$ and $TiO_2(Nd_2Ti_2O_7)$ or that of BaO and $TiO_2(BaTi_4O_9)$. The microstructure of ceramic with $BaO{\cdot}Nd_2O_3{\cdot}4TiO_2$ composition varied from spherical grains to needlelike grains with increasing sintering temperature. With increasing $Nd_2O_3$, the optimum sintering temperature with maximum density increased, and the dielectric constant(${\varepsilon}_r$) and quality factor(Q) decreased due to the formation of secondary phases. With increasing $TiO_2$, the optimum sintering temperature and the dielectric constant decreased with increased Q value. And the temperature coefficient of resonant frequency, ${\tau}_f$ shifted toward positive direction. The dielectric ceramics with $BaO/Nd_2O_3=1$ showed Q values of above 2000 and dielectric constants of above 80 at 3GHz.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.19 no.10
• /
• pp.971-975
• /
• 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 the Korean Ceramic Society
• /
• v.31 no.6
• /
• pp.651-659
• /
• 1994

BaTiO3 ceramics were sintered on Al2O3, MgAl2O4, MgO and Mg-, Ca-, Y-stabilized zirconia setters. Then the influence of setters on the microstructure of BaTiO3 ceramics and the stability of setters were investigated by SEM, EDAX and XRD analyses. The microstructure of BaTiO3 ceramics sintered on Al2O3, MgAl2O4, MgO and Mg-PSZ showed large grain growth, but little grain growth on Ce-TZP(Tetragonal Zirconia Policrystal). Mg-PSZ(Partially Stabilized Zirconia), Ca-PSZ, Ce-TZP setters showed extensive phase transformation. Y-TZP and fused Y-SZ (Stabilized Zirconia) setters were stable. The liquid sintering aids of BaTiO3 ceramics accelerate mass transport. The reaction of SrTiO3 in BaTiO3 with ZrO2 resulted in the formation of SrZrO3.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2011.05a
• /
• pp.31.2-31.2
• /
• 2011

We have investigated frequency dependant conductivity (or permittivity) of low dimensional oxide structures represented by [($Sr_{0.75}$, $La_{0.25}$)$TiO_3$]$_1$/1$[SrTiO_3]_n$ superlattices. The low dimensional oxide superlattice was made by cumulative stacking of one unit cell thick La doped $SrTiO_3$ and $SrTiO_3$ with variable thickness from 1 to 6 unit cell, i,e, [($Sr_{0.75}$, $La_{0.25}$)$TiO_3$]$_1$/$[SrTiO_3]_n$ (n=1, 2, 3, 4, 5, 6). We found two kinds of relaxation when n is 3 and 4, while, inductance component was observed at n=1. This behavior can be explained by electron modulation in ($Sr_{0.75}$, $La_{0.25}$)$TiO_3/SrTiO_3$ superlattices. When n is 1, electrons by La doping well extend to un-doped layer. Therefore, the transport of superlattices follows bulk-like behavior. On the other hand, as n increased, the doped electrons became two types of carrier: one localized and the other extended. These results in two kinds of transport phase. At further increase of n, most of doped electrons are localized at the doped layer. This result shows that dimensionality of the oxide structure significantly affect the transport of oxide nanostructures.

• Bulletin of the Korean Chemical Society
• /
• v.30 no.1
• /
• pp.201-204
• /
• 2009

$BaTiO_3/SrTiO_3$ and $PbTiO_3/PbZrO_3$ superlattice thin films were fabricated on $Pt/Ti/SiO_2/Si$ substrate by the pulsed laser deposition process. The morphologies and physical properties of deposited films were characterized by using X-ray diffractometer, HR-SEM, and Impedance Analyzer. XRD data and SEM images of the films indicate that each layer was well deposited alternatively in the superlattice structure. The dielectric constant of $BaTiO_3/SrTiO_3$ superlattice thin film was higher than that of individual $BaTiO_3$ or $SrTiO_3$ film. Same result was obtained in the $PbTiO_3/PbZrO_3$system. The dielectric constant of a superlattice film was getting higher as the number of layer is increased.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.8 no.3
• /
• pp.478-486
• /
• 1998

$CaTiO_3-x(La_{1/3}Nd_{1/3}TiO_3\;(0\le \textrm x\le0.8)$ system was prepared by reaction of $CaCO_3,\;LaO_3,\;Nd_2CO_3$ and ,TEX>$TiO_2$ mixture at 1673 K, which can be applied for microwave dielectric ceramic materials. The lattice parameters of(1-x))$CaTiO_3-x(La_{1/3}Nd_{1/3}TiO_3\;(0\le \textrm x\le0.8)$ system increased with the increase of x. Its structure was investigated by Rietveld profile-analysis of XRD in detail. Cations $ La^{3+}$ and Nd^{3+}$ were located at the $Ca^{2+}$ site in the range of $0\le \textrm x\le0.8$. crystal structure in $;(0\le \textrm x\le0.6)$ maintained space group Pnma with CaTiO_3 structure. The tiled and distorted $TiO_6$ was gradually released with the increase of x in $0\le \textrm x\le0.6$ .The structure was changed to a new space group of $Pmn2_1$ at the x value of 0.8. The relative dielectric constant $(\epsilon_r)$ of $(1-x)CaTiO_3-x(La_{1/3} Nd_{1/3})TiO_3$ ($(0\le \textrm x\le0.8)$) system was exponentially decreased by with the increased of x. The temperature coefficient of resonant frequency $(\tau_f)$ decreased with the increase of x in $0\le \textrm x\le0.6$ and then increased again at x=0.8 due to the change of crystal structure. The value of Q$\cdot f_o$ was 13800 (GHz) at x=0.2 and was very low under 2000 (GHz) in 0.4$\leq$x$\leq$0.8.

• Journal of Korean Society for Atmospheric Environment
• /
• v.24 no.1
• /
• pp.91-99
• /
• 2008

A multilayer tower-type photoreactor, in which $TiO_2$-coated glass-tubes were installed, was used to measure the vapor-phase BTEX removal efficiencies by ozone oxidation ($O_3$/UV), photocatalytic oxidation ($TiO_2$/UV) and the combination of ozone and photocatalytic oxidation ($O_3/TiO_2$/UV) process, respectively. The experiments were conducted under various relative humidities, temperatures, ozone concentrations, gas flow rates and BTEX concentrations. As a result, the BTEX removal efficiency and the oxidation rate by $O_3/TiO_2$/UV system were highest, compared to $O_3$/UV and $TiO_2$/UV system. The $O_3/TiO_2$/UV system accelerated the low oxidation rate of low-concentration organic compounds and removed organic compounds to a large extent in a fixed volume of reactor in a short time. Therefore, $O_3/TiO_2$/UV system as a superimposed oxidation technology was developed to efficiently and economically treat refractory VOCs. Also, this study demonstrated feasibility of a technology to scale up a photoreactor from lab-scale to pilot-scale, which uses (i) a separated light-source chamber and a light distribution system, (ii) catalyst fixing to glass-tube media, and (iii) unit connection in series and/or parallel. The experimental results from $O_3/TiO_2$/UV system showed that (i) the highest BTEX removal efficiencies were obtained under relative humidity ranging from 50 to 55% and temperature ranging from 40 to $50^{\circ}C$, and (ii) the removal efficiencies linearly increased with ozone dosage and decreased with gas flow rate. When applying Langmuir-Hinshelwood model to $TiO_2$/UV and $O_3/TiO_2$/UV system, reaction rate constant for $O_3/TiO_2$/UV system was larger than that for $TiO_2$/UV system, however, it was found that adsorption constant for $O_3/TiO_2$/UV system was smaller than that for $TiO_2$/UV system due to competitive adsorption between organics and ozone.

• Journal of the Korean Vacuum Society
• /
• v.11 no.3
• /
• pp.159-165
• /
• 2002

The physical properties of the TiN films deposited by ALD using $TiCl_4$and $NH_3$have been investigated. The TiN deposition rate is ~0.6 $\AA$ under an optimum deposition condition and the resistivity of the TiN films is 200~350 $\mu\Omega$cm . According to the XRD analysis results TiN films are crystallized in the ALD process window. AES analysis results show that the Cl impurity concentration in the TiN films is lower than 1 at% and that the atomic ratio of the TiN films is 1:1. Also it is found by SEM observation that the step coverage of the TiN films on which TiN films with trenches the aspect ratio of which is 10:1 is excellent.

• Journal of the Korean Magnetics Society
• /
• v.5 no.1
• /
• pp.64-70
• /
• 1995

The authors have studied crystallographic and magrletic properties of $NdFe_{10.7}TiM_{0.3}(M=B,\;Ti)$ by X-ray diffraction, VSM magnetometer, and Mossbauer spectrometer. The Alloys were prepared by arc-melting under argon atmosphere. The $NdFe_{10.7}TiM_{0.3}$ has pure single phase, whereas the $NdFe_{10.7}Ti_{1.3}$ contains some $\alpha-Fe$, from powder X-ray diffractometry. The $NdFe_{10.7}TiM_{0.3}$ has the $ThMn_{12}$-type tetragonal structure with $a_{0}=8.587\;{\AA}\;and\;c_{0}=4.788\;{\AA}$. The Curie temperature ($T_c$) is $570{\pm}3\;K$ from $M\"{o}ssbauer$ spectroscopy performed at various temperatures ranging from 13 to 770 K. Each spectrum of below $T_c$ was fitted with five subspectra of Fe sites in the structure ($8i_{1},\;8i_{2},\;8j_{1},\;8j_{2}\;and\;8f$). The area fraction of the subspectra at room temperature are 16.4, 8.2, 14.8, 21.3 and 39.3 %, respectively. Magenetic hyperfine fields for the Fe sites decrease in the order, $H_{hf}(8i)>H_{hf}(8j)>H_{hf}(8f)$.

• Corrosion Science and Technology
• /
• v.12 no.3
• /
• pp.119-124
• /
• 2013

Nano-multilayered, crystalline AlTiSiN thin films were deposited on WC-TiC-Co substrates by the cathodic arc plasma deposition. The deposited film consisted of wurtzite-type AlN, NaCl-type TiN, and tetragonal $Ti_2N$ phases. Their oxidation characteristics were studied at 800 and $900^{\circ}C$ for up to 20 h in air. The WC-TiC-Co oxidized fast with large weight gains. By contrast, the AlTiSiN film displayed superior oxidation resistance, due mainly to formation of the ${\alpha}-Al_2O_3$-rich surface oxide layer, below which an ($Al_2O_3$, $TiO_2$, $SiO_2$)-intermixed scale existed. Their oxidation progressed primarily by the outward diffusion of nitrogen, combined with the inward transport of oxygen that gradually reacted with Al, Ti, and Si in the film.