• Journal of the Korean Ceramic Society
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• v.49 no.1
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• pp.78-83
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• 2012

The electrophoretic deposition(EPD) of ZnO nano-sized colloids is investigated by changing the colloid number concentration, applied force, and deposition time. The change of the colloid size in a suspension was examined by the different colloid number concentrations (N = $3.98{\times}10^{15}$, N = $3.98{\times}10^{14}$, and N = $3.98{\times}10^{13}$) with an increase of the deposition time and applied forces. Deposition behavior was investigated by changing the applied fields (from DC 5 V to 50 V) and the deposition time (5 min to 25 min). The surface microstructures of the as-deposited films were investigated by SEM. The dried films were sintered from $850^{\circ}C$ to $1,050^{\circ}C$ for 2 h and then the microstructures were also explored by SEM. The agglomeration rate was enhanced by increasing the colloid number concentration of colloids. Colloid number concentration in a suspension must be rapidly decreased at higher values of the electric field. ZnO nano-sized colloids had the highest zeta potential value of over -28 mV in methanol. A homogeneous microstructure was obtained at colloid number concentration of N = $3.98{\times}10^{13}$, applied DC field of 5 V/cm and 15 min of deposition time at an electrode distance of 1.5 cm. Under these conditions, the deposited films were sintered at $850^{\circ}C$ and $1,050^{\circ}C$ for 2 h. The results show a typical pore-free surface morphology of a uniform thickness of 400 nm under these experimental conditions.

• Journal of the Korean Ceramic Society
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• v.45 no.3
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• pp.167-171
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• 2008

Zirconium-doped $Li_{1.1}Co_{1-x}Zr_xO_2(0{\leq}x{\leq}0.05)$ powders as cathode materials for lithium ion batteries were synthesized using an ultrasonic spray pyrolysis method. Cyclic voltammetry and cyclic stability tests were performed, and the changes of microstructure were observed. The solubility limit of zirconium into $Li_{1.1}CoO_2$ was less than 5 mol%, and monoclinic $Li_2ZrO_3$ phase was formed above the limit. The Zr-doping suppressed the grain growth and increased the lattice parameters of the hexagonal $LiCoO_2$ phase. The Zr-dopiong of 1mol% resulted in the best cyclic performance in the range of $3.0{\sim}4.3V$ at 1C rate (140 mA/g); the initial discharge capacity decreased from 158 mAh/g to 60 mAh/g in the undoped powder, while from 154 mAh/g to 135 mAh/g in the Zr-doped powder of 1 mol% after 30 cycles. The excellent cycle stability of Zr-doped powder was due to the low polarization during chargedischarge processes which resulted from the delayed collapse of the crystal structure of the active materials with Zr-doping.

• Journal of the Korean Ceramic Society
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• v.46 no.2
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• pp.189-199
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• 2009

The Powder characteristics and sintering behavior of $SiO_2$ coated $BaTiO_3$ were studied. $BaTiO_3$ powders were synthesized by the liquid mix method developed by Pechini, and silica coating was prepared by alkoxide hydrolysis method with TEOS and ethanol. The particle size of the $BaTiO_3$ powders was 35 nm and the thickness of the $SiO_2$ coating layer was 5 nm. As the $SiO_2$ content increased, the $SiO_2$ layers improved the powder dispersion by increasing electrostatic repulsion between the $BaTiO_3$ particles. Effects of MgO coating on microstructure and dielectric properties of $BaTiO_3$ have been studied compared with mechanically MgO mixed $BaTiO_3$. MgO coated $BaTiO_3$ particles were prepared by a homogeneous precipitation method using $MgCl_2\cdot 6H_2O$ and urea. MgO coated $BaTiO_3$ exhibited homogeneous microstructure compared with mixed samples. XRD analysis revealed that Mg substitution for the Ti site in the MgO mixed sample was much greater than in the coated one. Electrical properties of MgO mixed and coated $BaTiO_3$ were affected by the diffusion behavior of Mg in $BaTiO_3$ lattice.

• Journal of the Korean Ceramic Society
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• v.32 no.12
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• pp.1408-1416
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• 1995

Microstructure and ferroelectric properties of sol-gel derived PZT(52/48) and PT interlayered PZT(52/48) thin films on Pt/Ti/SiO2/Si substrates were investigated. Films were fabricated using Acetylacetone chelated PT and PZT(52/48) sols. PZT(52/48) thin films annealed at $700^{\circ}C$ for 20 min showed the rosette structure with the size of 1.2~1.6${\mu}{\textrm}{m}$ and the pyrochlore phse was contained. PT interlayered PZT thin films, which is inserted by PbTiO3 thin layer with the thickness of 130 $\AA$ between PZT thin film and electrode, consisted of a single perovskite phase after annealing above 55$0^{\circ}C$. They exhibited the uniform and columnar grains of 0.1~0.16${\mu}{\textrm}{m}$, which are applicable for microelectronic device including non-volatile memory. Typical P-E hysteresis loops could be obtained from PT interlayered PZT thin film at as low as the annealing temperature of 50$0^{\circ}C$. Ferroelectric properties of PT interlayered PZT thin films were improved as increasing annealing temperature up to $700^{\circ}C$, and then deteriorated at 75$0^{\circ}C$. PZT(52/48) and PT interlayered PZT(52/48) thin film annealed at $700^{\circ}C$ for 20 min displayed Ps=38.8$\mu$C/$\textrm{cm}^2$, Pr=10.0$\mu$C/$\textrm{cm}^2$, Ec=65.3 kV/cm and Ps=28.5$\mu$C/$\textrm{cm}^2$, Pr=9.8$\mu$C/$\textrm{cm}^2$, Ec=76.1 kV/cm, respectively.

• Journal of the Korean Ceramic Society
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• v.32 no.12
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• pp.1323-1330
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• 1995

The effects of various additives on the microstructures of sintered ZnO varistors were examined. Bi2O3, Sb2O3 and Cr2O3 were added to ZnO step by step to identify the effect of each component. The specimens were prepared by sintering at 110$0^{\circ}C$ and 120$0^{\circ}C$ in ambient atmosphere. In ZnO-Bi2O3-Sb2O3 ternary system, decrease of averge grain size due to antimony oxide addition depends on sintering temperature as well as Bi2O3 content. When Sb2O3 was partly or completely replaced by Cr2O3, grain size was further reduced. A significant amount of pyrochlore phase which was not transformed to spinel and Bi2O3-rich liquid phase seemed to remain during sintering at 110$0^{\circ}C$. Unlike ZnO-Bi2O3-Sb2O3 system, the $\alpha$-spinel phase containing significant amount of Cr did not transform to pyrochlore during furnace cooling. Fine spinel particles around 1${\mu}{\textrm}{m}$ size were ovserved within ZnO grains and grain boundaries, which were believed to be responsible for grain-growth inhibition in ZnO-Bi2O3-Sb2O3.

• Journal of the Korean Ceramic Society
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• v.36 no.4
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• pp.403-409
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• 1999

The dielectric and pyroelectric properties of $Ba_{0.66}$$Sr_{0.38}$$TiO_{3}$(BST) thin films growtn on Pt/Ti/NON/Si us-ing RF magnetron sputtering have been investigated. With increasing the substrate temperature during de-position of the BST film in the range of 300-$600^{\circ}C$ the dielectric and pyroelectric constants of the film were increased due to improved crystallinity of the film. In addition the dependence of the microstructural and electrical properties of BST films onthe deposition temperature of the bottom Pt electrode was studied. The preferred orientation of the BST films as well as the microstructure of the Pt film was greatly in-fluenced by the deposition temperature of the bottom Pt electrode was studied. The preferred orientation of the BSt films as well as the microstructure of the Pt film was greatly in-fluenced by the deposition temperature of the bottom Pt electrodes. and thus so were the pyrolelectric pro-perties of the BST film. The highest value of pyroelectric coefficient at room temperature obtained in this work was $nCcm^{-2}K^{-1}$ which is much higher than those previously reported on other perovskite fer-roelectric thin films.

• Journal of the Korean Ceramic Society
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• v.37 no.7
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• pp.673-680
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• 2000

The effect of excess PbO(0, 1, 2, 4, and 8 mol%) on grain growth and densification of (65)Pb(Mg1/3Nb2/3)O3-(35)PbTiO3 [mol%] ceramics has been investigaetd. With increasing the amount of excess PbO and sintering time, densities of sintered samples decreased gradually. The samples containing less than 1 mol% of PbO showed normal grain growth behavior, however abnormal grain growth was observed to occur in the samples with more than 2 mol% of PbO. In the samples with more than 2 mol% of PbO, the number of abnormal grains decreased and thus the average grain size became smaller with increasing the amount of excess PbO. These results demonstrated that the abnormal grain growth started to occur when a critical amount of excess PbO was added to a (65)Pb(Mg1/3Nb2/3)O3-(35)PbTiO3 sample. Since PMN-PT grains in a liquid matrix were angular, the observed abnormal grain growth was explained to proceed through the two dimensional nucleation process.

• Journal of the Korean Ceramic Society
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• v.51 no.5
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• pp.386-391
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• 2014

Silicon nitride ($Si_3N_4$) is regarded as one of the most promising materials for high temperature structural applications due to its excellent mechanical properties at both room and elevated temperatures. However, one high-temperature $Si_3N_4$ material intended for use in radomes has a relatively high dielectric constant of 7.9 - 8.2 at 8 - 10 GHz. In order to reduce the dielectric constant of the $Si_3N_4$, an in-situ reaction process was used to fabricate $Si_3N_4-SiO_2$-BN composites. In the present study, an in-situ reaction between $B_2O_3$ and $Si_3N_4$, with or without addition of BN in the starting powder mixture, was used to form the composite. The in-situ reaction process resulted in the uniform distribution of the constituents making up the composite ceramic, and resulted in good flexural strength and dielectric constant. The composite was produced by pressure-less sintering and hot-pressing at $1650^{\circ}C$ in a nitrogen atmosphere. Microstructure, flexural strength, and dielectric properties of the composites were evaluated with respect to their compositions and sintering processes. The highest flexural strength (193 MPa) and lowest dielectric constant (5.4) was obtained for the hot-pressed composites. The strength of these $Si_3N_4-SiO_2$-BN composites decreased with increasing BN content.

• Journal of the Korean Ceramic Society
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• v.39 no.10
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• pp.988-993
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• 2002

Electrochemical cells for decomposing $NO_x$ were fabricated using a hydrothermally synthesized lanthanum stannate pyrochlore catalyst. Thick film of the catalyst on the YSZ electrolyte disk was produced by screen-printing a paste consisted of $La_2Sn_2O_7$ and YSZ powders. Direct current was applied to the electrochemical cell to promote an electrochemical catalytic decomposition of $NO_x$. $NO_x$ decomposition behavior of the rectant gas mixture ($NO_x$ 0.1%, $O_2$ 2%) was investigated at 700${\circ}C$ under atmosphere pressure using on-line gas chromatography and $NO_x$ analyzer. It was observed that microstructure of the catalyst layer significantly influences the electrocatalystic decomposition of $NO_x$.

• Journal of the Korean Ceramic Society
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• v.38 no.7
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• pp.597-601
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• 2001

The effect of CuO, $B_2$ $O_3$, $V_2$ $O_{5}$ and CuO-B $i_2$ $O_3$additives on microwave dielectric properties of (P $b_{0.45}$C $a_{0.55}$) [(F $e_{0.5}$N $b_{0.5}$)$_{0.9}$S $n_{0.1}$] $O_3$(PCFNS) were investigated. The PCFNS ceramics were sintered at 11$65^{\circ}C$. To decrease the sintering temperature for using as a low-temperature co-firing ceramics (LTCC), CuO, $B_2$ $O_3$, $V_2$ $O_{5}$ and CuO-B $i_2$ $O_3$were added to the PCFNS. As the content of CuO increased, the sintered density and dielectric constant increased and the temperature coefficient of resonance frequency ($\tau$$_{f}$) shifted to the positive value. When the CuO-B $i_2$ $O_3$were added, dielectric properties were $\varepsilon$$_{r}$ of 83, Q. $f_{0}$ of 6085 GHz, and $\tau$$_{f}$ of 8ppm/$^{\circ}C$ at a sintering temperature of 100$0^{\circ}C$. The relationship between the microstructure and properties of ceramics was studied by X-ray diffraction and scanning electron microscopy.icroscopy.y.icroscopy.y.