• The Transactions of the Korean Institute of Electrical Engineers
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• v.44 no.4
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• pp.479-482
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• 1995

In this study, to improve sintering condition, anisotropic properties ( $k_{t}$/ $k_{p}$) of electromechanical coupling coefficient and piezoelectric constant $d_{h}$ and $g_{h}$, Mn $O_{2}$ impurity was added to the (P $b_{0.76}$C $a_{0.24}$)[( $Co_{1}$2/ $W_{1}$2/)$_{0.04}$ $Ti_{0.96}$] $O_{3}$ ceramics for application to hydrophone devices. Electromechanical coupling coefficients of the specimen with 1.5 [mol%] Mn $O_{2}$ sintered at 1150.deg. C were $k_{t}$=49% and $k_{p}$ = O, which exibited the highest value in piezoelectric anisotropic properties (kt/kp). Without relations with sintering temperature, the highest value of hydrostatic piezoelectric constant $d_{h}$ & $g_{h}$ were shown at the specimen with 1.5 [mol%] Mn $O_{2}$. Accordingly, the best addition amount of Mn $O_{2}$ was 1.5 [mol%] and proper sintering temperature was 1150.deg. C. Hydrostatic piezoelectric constant values of $d_{h}$=64.52[10$^{-12}$ C/N], $g_{h}$=35.92[10$^{-3}$ Vm/N] in the above condition were effectiely extended for hydrophone applications.pplications.ons.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.5
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• pp.498-503
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• 1999

La-doped $BaTiO_3$ ceramics were prepared from BaTiO(C_2O_4)_2\;{\cdot}\;XH_2O(BTO)$, which was synthesized by homogeneous precipitation using dimethyl oxalate. The electrical properties of La-doped $BaTiO_3$ were investigated with variation of La-contents and particle size. It was found that a large PTCR (positive temperature coefficient of resistivity) effect was appeared in the conditions at the 0.6 mol% of La-content and at small particle size of BTO as 1.0$\mu\textrm{m}$. The plot of temperature vs. 1/$\varepsilon_m$(T) above Curie temperature $(T_c)$ was agreed with Curie-Weiss law. The potential barrier calculated from measured resistance and capacitance of specimen, also gave higher value at small particle size of BTO as 1.0 $\mu\textrm{m}$ and at La-content of 0.6 mol%.

• Korean Journal of Materials Research
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• v.17 no.8
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• pp.414-419
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• 2007

We report the electrical conductivity of the mixed alkali silicate glasses in the system (60-x)$SiO_2-40Na_2O-xCaO(x=0\sim15wt%)$ in the temperature range from $150^{\circ}C$ to $620^{\circ}C$. In the range from $150^{\circ}C$ to glass transition temperature$(T_g)$, the electrical conductivities of glass samples had a tendency to be proportion with temperature. The glasses of containing over 7.5wt% CaO showed lower conductivities than the glasses of containing 0 and 5wt% CaO because two kinds of alkali ions$(Na^+,\;Ca^{2+})$ were obstructed each other. On the other hand, in the range from $T_g$ to $620^{\circ}C$, the electrical conductivity of glasses($7.5{\leq}x{\leq}12.5$) was unstable and decreased in some region. From XRD results, the $Na_4Ca(SiO_3)_3$ phase were observed in these glasses. This means the alkali ions didn't behave as carrier, it seems that this caused the conductivities decrease. In case of glass of containing 15wt% CaO, any crystal phase were not observed. This means the alkali ions behaved as carrier, it consequently seems the conductivity increased.

• Journal of the Korean Ceramic Society
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• v.34 no.12
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• pp.1227-1234
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• 1997

ZnO thin films were prepared by rf-magnetron sputter at various conditions. Crystallinity, microstructure, chemical composition, and optical composition, and optical properties of the films were investigated as functions of substrate temperature (R. T.-50$0^{\circ}C$) an sputter gas (O2/Ar=0-50%). ZnO thin films grown at 50$0^{\circ}C$ with sputter gas of pure argon as well as at R. T. with sputter gas of a mixture of argon & oxygen(O2/Ar=2%) exhibit a strong tendency of (002) preferred orientation, compared with a considerable random orientation at the other conditions. The thin films with (002) preferred orientation has a chemical stoichiometry of Zn/O-1.01, a band gap of 3.3eV, and a packing density of 98% respectively.

• Korean Journal of Materials Research
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• v.9 no.1
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• pp.104-107
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• 1999

We investigated the effects of cooling condition on deep levels and iron precipitate formation in iron-contaminated p-type silicon by DLTS(Deep Level Transient Spectroscopy) and preferential etching technique. Dependency of cooling condition on Bulk Micro-Defect (BMD) and four different iron-related deep traps were observed. For normal cooling condition, T1, T2, T3, T4 traps that related to Fe\ulcorner or Fe-O complex were obtained. However, the trap with activation energy, 0.4 eV was observed for slow cooling condition. The trap caused by the $\textrm{Fe}^{+}\textrm{}^{-}$ pair (H4:0.56eV) were detected only at the case of $\textrm{LN}_{2}$ quenching condition.

• Journal of the Korean Ceramic Society
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• v.33 no.9
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• pp.1057-1063
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• 1996

Y2O3-CeO2-ZrO2 powders were prepared from water-soluble salts using a coprecipitation method. The forming process of oxide and the characteristics of the calcined powders treated in different drying conditions were investigated. The oxidation was occurred at the temperature of around 40$0^{\circ}C$ and the main crystallization of ZrO2 around $600^{\circ}C$. On calcination at $600^{\circ}C$ heating lamp-dried powders consisted of agglomerates of globular morphology with average agglomerate size of 2.27${\mu}{\textrm}{m}$ and specific surface area of 68.3m2/g and spray dried powders contained dense spheric particles with average agglomerate size of 1.35${\mu}{\textrm}{m}$ and specific surface area of 11.0m2/g which exhibited low agglomeration tendency. Removal of the water by a freeze-drying technique produced calcined powders containing flake-like secondary particle structures with wide agglomerate size distri-bution of 0.1-60${\mu}{\textrm}{m}$ and specific surface area of 24.5${\mu}{\textrm}{m}$. The 20 MPa-pressed density (36.8-41.4% T,D) of calcined powders did not nealy depend on drying methods whilst compaction ratio of calcined powders derived from freeze-drying was the highest ( 6.24) among three drying methods. On continuous heating up to 150$0^{\circ}C$ the sinterability of calcined powders derived from heating lamp-drying was superior to those derived from spray-and freeze-drying. The final sintered density of calcined powders was the highest (96% T,D at 150$0^{\circ}C$) in case of heating lamp-drying.

• Korean Journal of Materials Research
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• v.24 no.12
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• pp.671-676
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• 2014

It is known that bones get damaged by accidents and aging. Since the discovery of Bioglass, various kinds of ceramics have been also found to bond to living bone; some of these ceramics are already being clinically used as bone-repairing materials. In the present study, antibacterial calcium silicate gel ($Ag-30CaO{\cdot}70SiO_2$ gel) was prepared by sol-gel method in order to control the microstructure, which is related to the dissolution rate and induction period of apatite formation in body environment. In addition, biological $Ag-30CaO{\cdot}70SiO_2$ is tested. This was done to impart antimicrobial activity to the $30CaO{\cdot}70SiO_2$. Ag ion was added during sol-gel synthesis to replace the $H_2O$ added during the making of the $30CaO{\cdot}70SiO_2$ gel, which has silver solutions of various concentration. After the sol-gel process, 1N-$HNO_3$ solution was used to wash the gel when synthesizing the gel, in order to maintain the porous structure and remove PEG, water soluble polymers. Then, the apatite forming ability of the sol-gel derived CaO-$SiO_2$ gels was investigated using simulated body fluid (SBF), which had almost the same ion concentration as that of human blood plasma. The gels were analyzed by FT-IR spectroscopy, SEM observation, XRD, and fluorescent microscopy. The apatite was successfully created even after washing the gel; apatite is present in an amorphous state, and was found to affect the concentration of the Ag ion in cells in MC3T3 live & dead assay results. From these results, it is suggested that a good material that can be used to repair defects of nature bone is $Ag-30CaO{\cdot}70SiO_2$ gel.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.4
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• pp.170-175
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• 2001

It was possible to grow the $Al_{2}O_{3}$ based $Y_{3}A_{5}O_{12}(YAG),ZrO_{2}$ binary and ternary eutectic fibers using micro-pulling down method with a growing rate of 0.1~15 mm/min. While $Al_{2}O_{3}/ZrO_{2}$ showed cellular-lamellar structure, $Al_{2}O_{3}$/YAG and $Al_{2}O_{3}$/YAG/$ZrO_{2}$ternary eutectic fibers showed homogeneous Chinese script lamellar structures. The microstructures of $Al_{2}O_{3}/ZrO_{2}$ binary eutectic fibers changed with solidification rate from lamellar pattern to cellular structure. The interlamellar spacing agreed with the inverse-square-root dependance on pulling rate according to $\lambda$=$kv_p\;{-1/2}$. $Al_{2}O_{3}/ZrO_{2}$ binary eutectic fibers recorded the highest tensile strength of about 1560MPa at room temperature. $Al_2O_3/YAG/ZrO_2$ternary eutectic fiber showed excellent thermal stability to $1200^{\circ}C$ without significant decrease. The maximum strength of ternary eutectic fibers recorded were 1100MPa at $25^{\circ}C$ and 970MPa at $1200^{\circ}C$, respectively.

• Kyungpook Mathematical Journal
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• v.47 no.3
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• pp.335-340
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• 2007

Let M be a hyperbolic 3-manifold such that ${\partial}M$ has at least two boundary tori ${\partial}_oM$ and ${\partial}_1M$. Suppose that M contains an essential orientable surface P of genus $g$ with one outer boundary component ${\partial}_oP$, lying in ${\partial}_oM$ and having slope ${\lambda}$ in ${\partial}_oM$, and $p$ inner boundary components ${\partial}_iP$, $i=1$, ${\cdots}$, $p$, each having slope ${\alpha}$ in ${\partial}_1M$. Let ${\beta}$ be a slope in ${\partial}_1M$ and suppose that $M({\beta})$ is toroidal. Let $\hat{T}$ be a minimal essential torus in $M({\beta})$, which means that $\hat{T}$ is pierced a minimal number of times by the core of the ${\beta}$-Dehn filling, among all essential tori in $M({\beta})$. Let $T=\hat{T}{\cap}M$ and denote by $t$ the number of components of ${\partial}T$. In this paper we prove: (i) if $t{\geq}3$, then ${\Delta}({\alpha},{\beta}){\leq}6+\frac{10g-5}{p}$, (ii) If $t=2$, then ${\Delta}({\alpha},{\beta}){\leq}13+\frac{24g-12}{p}$, (iii) If $t=1$, then ${\Delta}({\alpha},{\beta}){\leq}1$.

• Korean Journal of Materials Research
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• v.8 no.10
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• pp.925-930
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• 1998

EPMA and XPS on $Bi_2Sr_2-\chi_LCa_1+\chi_LCu_2O_{8+d}$($\chi_L$ = 0.01, 0.2, 0.3, 0.4, 0.5, 0.6) films by LPE method were performed in order to investigate Sr and Ca distributions in SrO- and Ca-layers. It is found that $T_C^{zero}$ carrier concentration and lattice parameter c monotonically decreases with increasing $\chi_L$. Sr and Ca contents in Ca-layer change in proportion to that in melt. On the other hand, in SrO-layer, Ca content strongly depends on Sr content in that layer and not on Ca content in melt. Since deficiency in SrO-layer increases and $T_C^{zero}$ creases with $\chi_L$,t is found that the deficiencies of Sr and Ca atoms in the SrO-layer has a influence on reducing $T_C^{zero}$.