• 한국재료학회지
• /
• 제12권8호
• /
• pp.600-607
• /
• 2002

The Ni-Zn synthetic ferrite were acquired from thermally decomposing the metal nitrates Fe(NO$_3$)$_3$.$9H_2$O, Zn($NO_3$)$_2$.$6H_2$O, Ni($NO_3$)$_2$. $6H_2$O, and Cu($NO_3$)$_2$. $3H_2$O at $150^{\circ}C$ for 24 hours and was calcined at $500^{\circ}C$. Each of those was pulverized for 3, 6, 9, and 12 hours in a steel ball mill and was sintered between $700^{\circ}C$ and $1,000^{\circ}C$ for 1 hour, and then their microstructures and electromagnetic properties were examined. We could make the initial specimens chemically bonded in liquid at the temperature as low as $150^{\circ}C$, by using the melting points less than $200^{\circ}C$ of the metal nitrates instead of the mechanical ball milling, then narrowed a distance between the particles into a molecular level, and thus lowed sintering temperature by at least $200^{\circ}C$ to$ 300^{\circ}C$. Their initial permeability was 50 to 400 and their saturation magnetic induction density and coercive force 2,400 G and 0.3 Oe to 0.5 Oe each, which were similar to those of Ni- Zn ferrite synthesized in the conventional process. In the graph of initial permeability vs frequencies, we could observe a $180^{\circ}C$rotation of the magnetic domain, which appears in a broad band of microwave near the resonance frequency.

• 한국전기전자재료학회논문지
• /
• 제30권7호
• /
• pp.454-458
• /
• 2017

$Bi_2Te_3$-based alloys have been intensively investigated as active materials for thermoelectric power generation devices from low-temperature (< $250^{\circ}C$) waste heat. In the present study, we fabricated Pb-doped, p-type $Bi_{0.48}Sb_{1.52}Te_3$ polycrystalline bulks by using meltsolidification and spark plasma sintering techniques, and evaluated their thermoelectric transport properties in an effort to develop optimized composition for low-temperature power generation applications. The electronic and thermal transport properties of $Bi_{0.48}Sb_{1.52}Te_3$ could be manipulated by Pb doping. As a result, the temperature for a peak thermoelectric performance (zT) gradually shifted toward higher temperatures with Pb content, suggesting that thermoelectric power generation efficiency can be enhanced by controlled Pb doping.

• 한국세라믹학회지
• /
• 제52권4호
• /
• pp.229-233
• /
• 2015

Currently, the majority of commercial white LEDs are phosphor converted LEDs made of a blue-emitting chip and YAG yellow phosphor dispersed in organic silicone. However, silicone in high-power devices results in long-term performance problems such as reacting with water, color transition, and shrinkage by heat. Additionally, yellow phosphor is not applicable to warm white LEDs that require a low CCT and high CRI. To solve these problems, mixing of green phosphor, red phosphor and glass, which are stable in high temperatures, is common a production method for high-power warm white LEDs. In this study, we fabricated conversion lenses with LUAG green phosphor, SCASN red phosphor and low-softening point glass for high-power warm white LEDs. Conversion lenses can be well controlled through the phosphor content and heat treatment temperature. Therefore, when the green phosphor content was increased, the CRI and luminance efficiency gradually intensified. Moreover, using high heat treatment temperatures, the fabricated conversion lenses had a high CRI and low luminance efficiency. Thus, the fabricated conversion lenses with green and red phosphor below 90 wt% and 10 wt% with a sintering temperature of $500^{\circ}C$ had the best optical properties. The measured values for the CCT, CRI and luminance efficiency were 3200 K, 80, and 85 lm/w.

• 한국재료학회지
• /
• 제14권8호
• /
• pp.595-599
• /
• 2004

We investigated the structural, electrical and magnetic properties of Mn-doped $CuAlO_2$ delafossite ceramics ($CuAl_{1-x}Mn_{x}O_2,\;0\le\;x\;\le0.05$), synthesized by solid-state reaction method in an air atmosphere at a sintering temperature of $1150^{\circ}C$. The solubility limit of Mn ions in delafossite $CuAlO_2$ was found to be as low as about 3 $mol\%$. Positive Hall coefficient and the temperature dependence of conductivity established that non-doped $CuAlO_2$ ceramic is a variable-range hopping p-type semiconductor. It was found that the Mn-doping in $CuAlO_2$ rapidly reduced the hole concentration and conductivity, indicating compensation of free holes. The analysis of the magnetization data provided an evidence that antiferromagnetic superexchange interaction is the dominant mechanism of the exchange coupling between Mn ions in $CuAl_{1-x}Mn_{x}O$ alloy, leading to an almost paramagnetic behavior in this alloy.

• 한국전기전자재료학회논문지
• /
• 제28권7호
• /
• pp.424-427
• /
• 2015

In this study, in order to develop the capacitor composition ceramics with the good dielectric properties, $(Ba_{0.86}Ca_{0.14})(Ti_{0.85}Zr_{0.12}Sn_{0.03})O_3+xCuO$ (x= 0.006~0.010) ceramics were prepared by the conventional solid-state reaction method. The effects of CuO addition on the microstructure and dielectric properties was investigated. All specimens indicated rhombohedral phase without any secondary phase. As CuO addition increased, the variation width of TCC was increased at more than $40^{\circ}C$. Also, the specimen with x=0.007 sintered at $1,250^{\circ}C$ showed the high dielectric constant of 9,632 in spite of low temperature sintering temperature.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 1998년도 추계학술대회 논문집
• /
• pp.45-48
• /
• 1998

A BaTiO$_3$ was annexed to SrTiO$_3$, (x)BaTiO$_3$-(1-x)SrTiO$_3$ (0.7$\leq$X$\leq$1) ceramics with stable dielectric and electrical properties in high voltage were manufactured. Structural, dielectric and electrical properties were surveyed with the contents of SrTiO$_3$. The open porosity and sintering density were excellent in 0.9BaTiO$_3$-0.1SrTiO$_3$, the grain size of 0.9BaTiO$_3$-0.1SrTiO$_3$ was maximum at 12.40[${\mu}{\textrm}{m}$]. Increasing SrTiO$_3$ mol ratio, the curie temperature was shifted low temperature and the supreme permittivity was increased. In line with increasing of supplied voltage, permitivity was decreased slightly.

• 전자공학회논문지A
• /
• 제29A권10호
• /
• pp.17-23
• /
• 1992

A ($Pb_{1-x}Ca_{x})ZrO_{3}$ system which has a high dielectric constant, low dielectric loss and temperature coefficient was investigated. For sintering temperatures above 1350$^{\circ}C$ the microstructures of sintered bodies were unchanged regardless of the amount of CaO. The dielectric constant and dielectric loss decreased and the temperature coefficient varied from positive to negative with the increasing amount of CaO. For the CaO content of 0.37, i.e. ($Pb_{0.63}Ca_{0.37})ZrO_{3}$, the ceramic showed very good dielectric properties such as ${\varepsilon}_1$=100, Q > 1200 at 3GHz, and T$_f$=$\pm$3ppm/$^{\circ}C$.

• 마이크로전자및패키징학회지
• /
• 제8권2호
• /
• pp.9-13
• /
• 2001

$(Ba_{0.5}Pb_{0.5})Nd_2Ti_5O_{14}$(마이크로파 유전체 세라믹스에 borosilicate계 유리를 첨가하여 저온소결 특성과 마이크로파 특성을 조사하였다. Borosilicate계 유리가 2~3 wt% 첨가된 경우 $950^{\circ}C$의 소결 온도에서 소결성이 향상됨과 동시에 품질계수도 놀아지는 것을 확인할 수 있었다. BPNT에 3 wt%의 유리를 첨가함으로써 $950^{\circ}C$에서 유전율은 90에서 75 정도로 약간의 감소를 보였으나 마이크로파 품질계수 (Q$\times$f)는 4500 정도로 잘 유지되었고 공진주파수의 온도계수도 +10 $ppm/^{\circ}C$로서 잘 유지되는 결과를 나타내었다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
• /
• pp.760-763
• /
• 2003

Low Temperature Cofired Ceramics (LTCC) technology is a promising technology to integrate many devices in a module by embedding passive components. For the module substrate, most LTCC structures have dielectric constants below 10 to reduce signal delay time. Some components, which need high dielectric constants, have not been yet embedded in LTCC module. So, embedding capacitor with high capacitance by applying another dielectrics with high dielectric constants in LTCC is an important issue to maximize circuit density in LTCC module. In this study, electrical properties of embedded capacitor fabricated by dielectric paste of high dielectric constants (K-100) and co-firing behavior with LTCC were investigated. To prevent camber development of co-fired structure, constrained sintering process was tested. Dielectric properties of embedded capacitors were calculated from their capacitance and impedance value. Temperature coefficient of capacitance were also measured.

• 한국세라믹학회지
• /
• 제33권1호
• /
• pp.17-24
• /
• 1996

Pb(Mg1/3Nb2/3)O3 powder with high purity chemical homogeniety and reactivity was prepared by solvent eva-poration of common solution. The common solution was fabricated using a Pb(NO3)2 Mg(NO)3 and NB solution which was prepared by dissolving NbC in H2O2 acquous solution. In precusor powder prepared by solvent evaporation method the synthetic temperature of Pb(Mg1/3 Nb2/3)O3 phase was lowered. And the formation of homogeneous Pb(Mg1/3Nb2/3)O3 phase was enhanced but the formation of pyrochlore phase was reduced. The dielectric constant of PMN ceramics from the synthesized powder was found to increase with both sintering temperature and excess MgO and subsequent analysis of the microstructures confirmed that this was due to an increase in grain size. The grain size dependence is explained as a consequence of low-permittivity grain boundaries.