• 한국재료학회지
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• 제24권9호
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• pp.495-501
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• 2014

Despite having many attractive properties, $ZrO_2$ ceramic has a low fracture toughness which limits its wide application. One of the most obvious tactics to improve its mechanical properties has been to add a reinforcing agent to formulate a nanostructured composite material. Nanopowders of $ZrO_2$ and Cr were synthesized from $CrO_3$ and Zr powder by high energy ball milling for 10 h. Dense nanocrystalline $2/3Cr-ZrO_2$ composite was consolidated by a high-frequency induction heated sintering method within 5 min at $600^{\circ}C$ from mechanically synthesized powder. The method was found to enable not only rapid densification but also the inhibition of grain growth, preserving the nano-scale microstructure. Highly dense $2/3Cr-ZrO_2$ composite with relative density of up to 99.5% was produced under simultaneous application of a 1 GPa pressure and the induced current. The hardness and fracture toughness of the composite were 534 kg/mm2 and $7MPa{\cdot}m1/2$, respectively. The composite was determined to have good biocompatibility.

• 한국결정성장학회지
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• 제30권5호
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• pp.163-167
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• 2020

본 연구에서는 PVT(Physical Vapor Transport) 방법을 이용하여 반도체 식각 공정용 소재로 사용되는 링 모양의 SiC(Silicon carbide) 다결정을 제조하였다. 흑연 도가니 내부에 원기둥 모양의 흑연 구조물을 배치하여 PVT법에 의한 링 모양의 SiC 다결정을 성장시켰다. 성장된 결정은 Raman 및 UVF(Ultra Violet Fluorescence) 분석을 이용하여 결정의 상분석을 하였고, SEM(Scanning Electron Microscope), EDS(Energy Dispersive Spectroscopy) 분석을 통해 미세조직 및 성분을 확인하였다. PVT 성장 초기의 온도변화를 통하여 SiC 다결정의 결정립 크기와 성장 속도를 조절할 수 있었다.

• ETRI Journal
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• 제18권1호
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• pp.15-27
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• 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.

• 센서학회지
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• 제15권3호
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• pp.216-221
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• 2006

ZnO thin films prepared by PLD method exhibit an excellent optical property, but may have some problems such as incomplete surface roughness and crystallinity. In this study, undoped ZnO buffer layers were deposited on (0001) sapphire substrates by ultra high vacuum pulse laser deposition (UHV-PLD) and molecular beam epitaxy (MBE) methods, respectively. After post annealing of ZnO buffer layer, undoped ZnO thin films were deposited under different oxygen pressure ($35{\sim}350$ mtorr) conditions. The Arsenic-doped (1, 3 wt%) ZnO thin layers were deposited on the buffer layer of undoped ZnO by UHV-PLD method. The optical property of the ZnO thin films was analyzed by photoluminescence (PL) measurement. The ${\theta}-2{\theta}$ XRD analysis exhibited a strong (002)-peak, which indicates c-axis preferred orientation. Field emission-scanning electron microscope (FE-SEM) revealed that microstructures of the ZnO thin films were varied by oxygen partial pressure, Arsenic doping concentration, and deposition method of the undoped ZnO buffer layer. The denser and smoother films were obtained when employing MBE-buffer layer under lower oxygen partial pressure. It was also found that higher Arsenic concentration gave the enhanced growing of columnar structure of the ZnO thin films.

• Transactions on Electrical and Electronic Materials
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• 제12권2호
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• pp.72-75
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• 2011

In this study, $(K_{0.5}Na_{0.5})(Nb_{0.97}Sb_{0.03})O_3+0.9$ mol% $K_{5.4}Cu_{1.3}Ta_{10}O_{29}+x$ mol% $K_4CuNb_8O_{23}$ (x = 0, 0.2, 0.6, 0.8) ceramics were prepared by a conventional mixed oxide method. Their microstructure and electric properties were investigated. The secondary phase was made by virtue of $K_4CuNb_8O_{23}$ (KCN) addition in the $(K_{0.5}Na_{0.5})(Nb_{0.97}Sb_{0.03})O_3$ system ceramics. However, the sinterability of the ceramics increased with increasing $K_4CuNb_8O_{23}$ content. At the 0.6 mol% $K_4CuNb_8O_{23}$ added composition ceramics sintered at $1,060^{\circ}C$, kp and $d_{33}$ showed the optimum values of 0.39 and 145 pC/N, respectively, suitable for piezoelectric actuator application.

• 한국전기전자재료학회논문지
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• 제27권9호
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• pp.555-560
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• 2014

In this paper, in order to develop outstanding Pb-free composition ceramics, the $Fe_2O_3$-doped ($Na_{0.525}K_{0.443}Li_{0.037}$)($Nb_{0.883}Sb_{0.08}Ta_{0.037}$)$O_3$ + 0.3 wt% $Bi_2O_3$ + x wt% $Fe_2O_3$ (x= 0~1.0 wt%)(abbreviated as NKL-NST) lead-free piezoelectric ceramics have been synthesized using the ordinary solid state reaction method. The effect of $Fe_2O_3$-doping on their microstructure and electrical properties were investigated. XRD diffraction pattern studies confirm that $Fe_2O_3$ completely diffused into the NKL-NST lattice to form a new stable soild solution with $Fe^{3+}$ entering the $Nb^{5+}$, $Sb^{5+}$ and $Ta^{5+}$ of B-site. And, phase structure of all the ceramics exhibited pure perovskite phase and no secondary phase was found in the ceramics. The ceramics doped with 0.6 wt% $Fe_2O_3$ have the optimum values of piezoelectric constant($d_{33}$), planar piezoelectric coupling coefficient($k_p$) and mechanical quality factor($Q_m$) : $d_{33}$ = 233 [pC/N], $k_p$= 0.44, $Q_m$= 95. These results indicate that the ($Na_{0.525}K_{0.443}Li_{0.037}$)($Nb_{0.883}Sb_{0.08}Ta_{0.037}$)$O_3$ +0.3 wt% $Bi_2O_3$ + 0.6 wt% $Fe_2O_3$ ceramic is a promising candidate for lead-free piezoelectric ceramics.

• Tribology and Lubricants
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• 제16권2호
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• pp.121-125
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• 2000

Silicon nitride ceramic has been verified as an excellent rolling bearing material because of its high strength and outstanding rolling fatigue life properties. However under some corrosive circumstances it showed drawbacks such as hardness reduction and severe wear caused by corrosion. In this work, the variations of the rolling wear and hardness of three kinds of ceramics were studied for the specimen aged 15 days in alkali water (90 $\pm$ 2$\^{C}$,25 wt% NaOH ). All of the specimens, ① Si$_3$N$_4$, ② 3Y-TZP and ③ 3Y-TZP alloyed with 5 wt% CeO$_2$, were sintered and post-HIPed, and then polished up to 0.02 $\mu$mRa of surface roughness. Rolling wear tests were conducted by MJ type rolling fatigue life tester under the initial theoretical maximum contact stress of 3.16 GPa and the spindle speed of 1,000 rpm. Spindle oil was used as a lubricant. The specimens were not worn before aging. For the specimen aged in alkali water, Si$_3$N$_4$ and 3Y-TZP were worn by rolling wear tests, and hardness was decreased. While aging the specimens, the phase was transformed from tetragonal to monoclinic in 3Y-TZP and the microstructure change occurred in Si$_2$N$_4$. 3Y-TZP specimens alloyed with 5 wt% CeO$_2$ were not worn after aging and no phase transformation occurred while aging.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.319-319
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• 2013

Even though the fabrication methods of metal oxide based thin film capacitor have been well established such as RF sputtering, Sol-gel, metal organic chemical vapor deposition (MOCVD), ion beam assisted deposition (IBAD) and pulsed laser deposition (PLD), an applicable capacitor of printed circuit board (PCB) has not realized yet by these methods. Barium Strontium Titanate (BST) and other high-k ceramic oxides are important materials used in integrated passive devices, multi-chip modules (MCM), high-density interconnect, and chip-scale packaging. Thin film multi-layer technology is strongly demanded for having high capacitance (120 nF/$mm^2$). In this study, we suggest novel multi-layer thin film capacitor design and fabrication technology utilized by plasma assisted deposition and photolithography processes. Ba0.6Sr0.4TiO3 (BST) was used for the dielectric material since it has high dielectric constant and low dielectric loss. 5-layered BST and Pt thin films with multi-layer sandwich structures were formed on Pt/Ti/$SiO_2$/Si substrate by RF-magnetron sputtering and DC-sputtering. Pt electrodes and BST layers were patterned to reveal internal electrodes by photolithography. SiO2 passivation layer was deposited by plasma-enhanced chemical vapor deposition (PE-CVD). The passivation layer plays an important role to prevent short connection between the electrodes. It was patterned to create holes for the connection between internal electrodes and external electrodes by reactive-ion etching (RIE). External contact pads were formed by Pt electrodes. The microstructure and dielectric characteristics of the capacitors were investigated by scanning electron microscopy (SEM) and impedance analyzer, respectively. In conclusion, the 0402 sized thin film multi-layer capacitors have been demonstrated, which have capacitance of 10 nF. They are expected to be used for decoupling purpose and have been fabricated with high yield.

• The Korean Journal of Ceramics
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• 제2권1호
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• pp.11-18
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• 1996

The variation of electrical conductively and Seebeck coefficient of FeSi2 according to the density of the specimen has been observed over the temperature range 50 to $700^{\circ}C$. A conventional pressureless sintering method with various sintering time (0, 0.5, 1, 5h) at $1190^{\circ}C$ and/or various sintering temperatures(1160, 1175, 1190, $1200^{\circ}C$) for 2 h was carried out to prepare $FeSi_2$ specimens having various densities. The relationship between the electrical conductivity and Seebeck coefficient was investigated after two steps of annealing (at $865^{\circ}C$ and then $800^{\circ}C$ for total 160h) and thermoelectric measurement. The electrical conductivity for the specimens showed a typical tendency of semiconductor, the average activation energy of which in the intrinsic region (above $300^{\circ}C$) was observed approximately as 0.452 eV, and increased slightly with density. On the other hand, the specimen of the lower density showed the higher value of Seebeck coefficient in the intrinsic region. As the temperature fell into the non-degenerate region, the highly densified specimen which had relatively little residual metal phase showed the higher value of Seeback coefficient. The power factor of all specimens showed the optimum value at $200^{\circ}C$. However, the power factor of the specimen of the lower density increased again from $400^{\circ}C$ and that of the higher dense specimen increased from $500^{\circ}C$. The power factor was more affected by Seebeck coefficient than electrical conductivity over all temperature range.

• 한국전기전자재료학회논문지
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• 제26권2호
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• pp.104-108
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• 2013

In this paper, the $0.95(Na_{0.5}K_{0.5})_{0.04}[(Nb_{0.8}Ta_{0.20})_{0.994}Co_{0.015}]O_3$(abbreviated as NKNT) + $0.05KNbO_3$ lead-free piezoelectric ceramics were synthesized by the conventional mixed oxide method route with normal sintering. And also, the effects of calcination temperature on the microstructure, dielectric properties, and piezoelectric properties were investigated. A polymorphic phase transition(PPT) between orthorhombic and tetragonal phases was observed in specimens calcined at $810^{\circ}C{\sim}850^{\circ}C$. The ceramics calcined at $830^{\circ}C$ showed excellent piezoelectric properties: $d_{33}$= 179 pC/N, $k_p$= 0.384, $Q_m$= 79.73). These results indicate that the ceramic is a promising candidate material for lead-free piezoelectric ceramics.