• 한국세라믹학회지
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• 제51권4호
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• pp.265-270
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• 2014

Among the Ruddlesden-Popper series, $La_4Ni_3O_{10}$ has received widespread attention as a promising cathode material by reason of its favorable properties for realizing high performance of intermediate temperature solid oxide fuel cells (IT-SOFCs). The $La_4Ni_3O_{10}$ cathode is prepared using the facile sol-gel method by employing tri-blockcopolymer (F127) to obtain a single phase in a short sintering time. There are no reactions between the $La_4Ni_3O_{10}$ cathode and the $Ce_{0.9}Gd_{0.1}O_{2-\delta}$ (GDC) electrolyte upon sintering at $1000^{\circ}C$, indicating that the $La_4Ni_3O_{10}$ cathode has good chemical compatibility with the GDC electrolyte. The maximum electrical conductivity of $La_4Ni_3O_{10}$ reaches approximately 240 S $cm^{-1}$ at $100^{\circ}C$ and gradually decreases with increasing temperaturein air atmosphere. The area specific resistance value of $La_4Ni_3O_{10}$ composite with 40 wt% GDC is $0.435{\Omega}cm^2$ at $700^{\circ}C$. These data allow us to propose that the $La_4Ni_3O_{10}$-GDC composite cathode is a good candidate for IT-SOFC applications.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 추계학술대회 논문집 학회본부 C
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• pp.479-481
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• 2000

The effect of $Al_{2}O_{3}+Y_{2}O_{3}$ additives on fracture toughness of $\beta-SiC-TiB_2$ composites by hot-pressed sintering were investigated. The f$\beta-SiC-TiB_2$ ceramic composites were hot-presse sintered and annealed by adding 16, 20, 24wt% $Al_{2}O_{3}+Y_{2}O_{3}$(6 : 4wt%) powder as a liquid forming additives at low temperature($1800^{\circ}C$) for 4h. In this microstructures, the relative density is over 95.88% of the theoretical density and the porosity increased with increasing $Al_{2}O_{3}+Y_{2}O_{3}$ contents because of the increasing tendency of pore formation. The fracture toughness showed the highest of $5.88MPa{\cdot}m^{1/2}$ for composites added with 20wt% $Al_{2}O_{3}+Y_{2}O_{3}$ additives at room temperature. The electrical resistivity showed the lowest of $5.22{\times}10^{-4}\Omega{\cdot}cm$ for composite added with 20wt% $Al_{2}O_{3}+Y_{2}O_{3}$ additives at room temperature and is all positive temperature coefficient resistance (PTCR) against temperature up to $700^{\circ}C$.

• Journal of Power Electronics
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• 제16권6호
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• pp.2119-2128
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• 2016

Due to detection and control errors, some high-frequency harmonics with voltage-source characteristics cause circulating currents in modular inverters. Moreover, the circulating currents are usually affected by the output filters (OF) of each module due to their filter and resonance properties. The interaction among the circulating currents in the modules increase the power loss and reduce system stability and control precision. Therefore, this paper reports the results of a study on the SPWM high-frequency harmonics circulating currents for a double-module VSI. In the paper, an analysis of the circulating-current circuits is briefly described. Next, a mathematic model of the single-module output voltage based on the carrier frequency of SPWM is built. On this basis, through mathematic modeling of high-frequency harmonic circulating currents, the formation mechanism and distribution characteristics of circular currents and their influences are studied in detail. Finally, the influences of the OF on the circulating currents are studied by mainly taking an LC-type filter as an example. A theoretical analysis and experimental results demonstrate some important characteristics. First, the carrier phase shifting of the SPWM for each module is the major cause of the SPWM harmonic circulating currents, and the circulating currents are in an odd distribution around n-times the carrier frequency $n{\omega}_s$, where n = 1, 2, 3, ${\ldots}$. Second, the harmonic circular currents do not flow into the parallel system. Third, the OF can effectively suppress the non-circulating part of the high-frequency harmonic currents but is ineffective for the circulation part, and actually reduces system stability.

• 한국결정성장학회지
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• 제3권2호
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• pp.140-148
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• 1993

As-Se-Ge 3원계 칼코게나이드 유리의 비정질화와 결정화 및 박막화를 통하여 전기적, 광학적 특성을 평가코자 하였다. 조성의 범위는$As_{20~50}, Se_{40~70}, Ge_{10~40}$ at%였으며, Se을 40 at%로 고정시 As가 30 at%이상일 때 급격한 전기전도도의 증가를 가져왔으며,$As_{20}Se_{50}Ge_{30}$을 결정화시킨 경우, $476^{\circ}C$에서 3시간 결정을 성장시켰을 때의 전기전도도가 가장 양호하였으며, 주결정상으로 $GeSe_2와 As_2Se_3$의 흔정을 관찰할 수 있었다. 박막에서는1.8~2.4eV의 광에너지 영역에서 $2{times}10^3~7{times}10^4$의 광흡수계수를 나타냈고, 1.85eV의 광학적 에너지 갭을 나타냈다.

• 한국전기전자재료학회논문지
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• 제26권1호
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• pp.22-26
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• 2013

PTCR ceramics of $(Ba_{0.998}Sm_{0.002})TiO_3+0.001MnCO_3+xSiO_2$ (x=1, 2, 3, 4, 5, 6 mol%) were fabricated by solid state method. Disk samples of diameter 5 mm and thickness about 1mm were sintered at $1,290^{\circ}C$ for 2 h in reduced atmosphere of $5%H_2-95%N_2$ followed by re-oxidation at $600^{\circ}C$ for 30 min. in $20%O_2-80%N_2$.and their microstructures and electrical properties were investigated with SEM and Multimeter. The color of sintered samples was strongly dependent on $SiO_2$ content showing that the color of samples with $SiO_2$ of 1~2 mol% was gray but that of samples with $SiO_2$ of 4~6 mol% was changed from gray to blue, which seems to be related with the reduction of samples due to the oxygen vacancies created during the sintering in reduced atmosphere. $SiO_2$ content had a great influence on the microstructure and the electrical properties. With increasing $SiO_2$ content, the grain size of samples increased and the resistivity as well as the resistivity jump ($R_{285}/R_{min}$) decreased, which is considered to be attributed to the resistivity change at grain interior and grain boundary due to the fast mass transfer through $SiO_2$ liquide phase during the sintering. Samples with 2 mol% $SiO_2$ has the resistivity of $202{\Omega}cm$ and the resistivity jump of 3.28. It is expected that $SiO_2$ doped $BaTiO_3$ based PTC ceramics can be used for multilayered PTC thermistor due to the resistance to the sintering in reduced atmosphere.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권5호
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• pp.221-225
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• 2001

The effect of $Al_2O_3+Y_2O_3$ additives on fracture toughness of ${\beta}-SiC-TiB_2$ composites by hot-pressed sintering was investigated. The ${\beta}-SiC-TiB_2$ ceramic composites were hot-press sintered and pressureless-annealed by adding 16, 20, 24 wt% ${\beta}-SiC-TiB_2$(6:4 wt%) powder as a liquid forming additives at low temperature(1800 $^{\circ}C$) for 4 h. Phase analysis of composites by XRD revealed mostly of ${\alpha}$-SiC(6H), $TiB_2$, and YAG($Al_5Y_3O_{12}$). The relative density was over 95-88 % of the theoretical density, and the porosity increased with increasing $Al_2O_3+Y_2O_3$ contents because of the increasing tendency of pore formation. The fracture toughness showed the highest value of 5.88 MPa${\cdot}m^{1/2}$ for composites added with 20 wt% $Al_2O_3+Y_2O_3$ additives at room temperature. The electrical resistivity showed the lowest value of $5.22{\times}10^{-4}\;{\Omega}\;{\cdot}\;cm$ for composite added with 20 wt% $Al_2O_3+Y_2O_3$ additives at room temperature, and was all positive temperature coefficeint resistance(PTCR) against temperature up to 900 $^{\circ}C$.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1990년도 추계학술대회 논문집
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• pp.65-67
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• 1990

In this study, (0.80-x)Pb($Mg_{1/3}Nb_{2/3}$)$O_3$-$PbTiO_3$-Pb($Ni_\frac{1}{2}W_\frac{1}{2}$)$O_3$ 0.05$\leq$x$\leq$0.20) ceramics were fabricated by the mixed oxide method, the sintering temperature and time were 950∼1200[$^{\circ}C$], 2[hr], respectively. The dielectric and structural properties with composition and sintering temperature were investigated for the application as multilayer ceramic capacitors. Dielectric constant of 0.70PMN-0.2PT-0.10PNW composition with repeated calcination was increased rapidly. Increasing the Pb($Mg_{1/3}Nb_{2/3}$)$O_3$-$PbTiO_3$-Pb($Ni_\frac{1}{2}W_\frac{1}{2}$)$O_3$ contents from 0.05 to 0.20 [mol], phase transition temperature was shifted from 68 to 2[$^{\circ}C$] and dielectric constant was decreased while sintered density was increased. In the specimens containing 0.10, 0.15[mol] of PNW, dielectri constants at room temperature were exhibited the highest values 11199, 10114, respectively. Resistivity of specimens were $10^{10}$ ∼ $10^{12}$($\Omega$.m) and there was no dependence on sintering temperature and composition.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 C
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• pp.2410-2412
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• 2005

In this study, two types of PS substrate were fabricated for sensing of chemical and biological substances. For sensing of the humidity and chemical analyzes such as $CH_3OH$ or $C_2H_5OH$, PS layers are prepared by photoelectrochemical etching of silicon wafer in aqueous hydrofluoric acid solution. To evaluate their sensitivity, we measured the resistance variation of the PS diaphragm. As the amplitude of applied voltage increases from 2 to 6Vpp at constant frequency of 5kHz, the resistance variation for humidity sensor rises from 376.3 to $784.8{\Omega}$/%RH. And the sensitivities for $CH_3OH$ and $C_2H_5OH$ were 0.068 uA/% and 0.212 uA/%, respectively. For biological sensing application, amperometric urea sensors were fabricated based on porous silicon(PS), and planar silicon(PLS) electrode substrates by the electrochemical methods. Pt thin film was sputtered on these substrates which were previously formed by electrochemical anodization. Poly (3-methylthiophene) (P3MT) were used for electron transfer matrix between urease(Urs) and the electrode phase, and Urs also was by electrochemically immobilized. Effective working area of these electrodes was determined for the first time by using $Fe(CN)_6^{3-}/Fe(CN)_6^{4-}$ redox couple in which nearly reversible cyclic voltammograms were obtained. The $i_p$ vs $v^{1/2}$ plots show that effective working electrode area of the PS-based Pt thin film electrode was 1.6 times larger than the PLS-based one and we can readily expect the enlarged surface area of PS electrode would result in increased sensitivity by ca. 1.6 times. Actually, amperometric sensitivity of the Urs/P3MT/Pt/PS electrode was ca 0.91uA/$mM{\cdot}cm^2$, and that of the Urs/P3MT/Pt/PLS electrode was ca. 0.91uA/$mM{\cdot}cm^2$ in a linear range of 1mmol/L to 100mmol/L urea concentrations

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 Techno-Fair 및 추계학술대회 논문집 전기물성,응용부문
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• pp.124-125
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• 2007

The composites were fabricated $\beta$-SiC and $TiB_2$ powders with the liquid forming additives of 8, 12, 16[wt%] $Al_2O_3+Y_2O_3$ as a sintering aid by pressureless annealing at $1,650[^{\circ}C]$ for 4 hours. Reactions between SiC and transition metal $TiB_2$ were not observed in the microstructure and the phase analysis of the pressureless annealed SiC-$TiB_2$ electroconductive ceramic composites. The relative density, the flexural strength, the Young's modulus and the Vicker's hardness showed the highest value of 82.29[%], 189.5[MPa], 54.60 [GPa] and 2.84[GPa] for SiC-$TiB_2$ composites added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at room temperature. The relative density of SiC-$TiB_2$ composites was lowered due to gaseous products of the result of reaction between SiC and $Al_2O_3+Y_2O_3$. The electrical resistivity showed the lowest value of 0.012[${\Omega}{\cdot}cm$] for 16[wt%] at 25[$^{\circ}C$]. The electrical resistivity was all negative temperature coefficient resistance (NTCR) in the temperature ranges from 25[$^{\circ}C$] to 700[$^{\circ}C$].

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1303-1304
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• 2007

The composites were fabricated, respectively, using 61[vol.%]SiC-39[vol.%]$TiB_2$ and using 61[vol.%]SiC-39[vol.%]$ZrB_2$ powders with the liquid forming additives of 12[wt%] $Al_{2}O_{3}+Y_{2}O_{3}$ by hot pressing annealing at $1650[^{\circ}C]$ for 4 hours. Reactions between SiC and transition metal $TiB_2$, $ZrB_2$ were not observed in this microstructure. ${\beta}{\rightarrow}{\alpha}$-SiC phase transformation was occurred on the SiC-$TiB_2$ and SiC-$ZrB_2$ composite. The relative density, the flexural strength and Young's modulus showed the highest value of 98.57[%], 226.06[Mpa] and 86.38[Gpa] in SiC-$ZrB_2$ composite at room temperature respectively. The electrical resistivity showed the lowest value of $7.96{\times}10^{-4}[{\Omega}{\cdot}cm]$ for SiC-$ZrB_2$ composite at $25[^{\circ}C]$. The electrical resistivity of the SiC-$TiB_2$ and SiC-$ZrB_2$ composite was all positive temperature coefficient resistance (PTCR) in the temperature ranges from $25[^{\circ}C]$ to $700[^{\circ}C]$. The resistance temperature coefficient of composite showed the value of $6.88{\times}10^{-3}/[^{\circ}C]$ and $3.57{\times}10^{-3}/[^{\circ}C]$ for SiC-$ZrB_2$ and SiC-$TiB_2$ composite in the temperature ranges from $25[^{\circ}C]$ to $700[^{\circ}C]$.