• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.12
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• pp.781-785
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• 2016

With trend of the miniaturization and the high-functionalizing of mobile communication system, low-loss microwave dielectric materials are widely used for high frequency communication components. These dielectric materials should be co-sintered with highly electric-conducting metal such as silver or copper for high-frequency and thick film process application. Sintering temperature of $Ca(Li_{1/3}Nd_{2/3})_{0.2}Ti_{0.8}]O_{3-{\delta}}$, which has excellent dielectric properties such as ${\varepsilon}_r$ above 40, quality factor ($Q{\cdot}f_0$) above 16,000 GHz, and TCF (temperature coefficient of resonant frequency) of $-20{\sim}-10ppm/^{\circ}C$, is reported as high as $1,175^{\circ}C$, so it could not be co-sintered with silver or copper. Therefore in this study, low-temperature melting glasses of Zn-B-O and Zn-B-Si-O systems were added to $Ca[(Li_{1/3}Nb_{2/3})_{0.8}Ti_{0.2}]O_{3-{\delta}}$ to lower its sintering temperature under $900^{\circ}C$ without losing excellency of dielectric properties. With 15 weight % of Zn-B-Si-O glass and sintered at $875^{\circ}C$, specimen showed density of $4.11g/cm^3$, ${\varepsilon}_r$ of 40.1, $Q{\cdot}f_0$ of 4,869 GHz, and TCF of $-5.9ppm/^{\circ}C$. With 15 weight % of Zn-B-O glass and sintered at $875^{\circ}C$, specimen showed density of $4.14g/cm^3$, ${\varepsilon}_r$ of 40.4, $Q{\cdot}f_0$ of 7,059 GHz, and TCF of $-0.92ppm/^{\circ}C$.

• Journal of the Korean Magnetics Society
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• v.18 no.3
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• pp.120-125
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• 2008

In this study, NiCoZn ferrites with the variation of sintering temperature and chemical composition were prepared by the coprecipitation. Microstructures Crystal structure of NiCoZn ferrites were analyzed by XRD and their electric magnetic characteristics were analyzed by LCR meter and their morphology observed by SEM. We identified that these powders have a typical NiCoZn spinel structure and nanoparticles average size of 40 nm. The impurity, the initial permeability and the Q factor value are the lowest of sintered NiCoZn ferrite at $1250^{\circ}C$. Also, we measured S-parameter for $(Ni_{0.4}Co_{0.1}Zn_{0.5})Fe_2O_4$ which showed a maximum reflection loss of -3.1 dB at 6 GHz for the 2 mm thick sample. From this result, we found that the NiCoZn ferrite can be used in ferrite microwave-absorbing application at a higher frequency region (> 6 GHz).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.838-841
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• 2004

[ $B_2O_3$ ] added $Ba(Mg_{1/3}Nb_{2/3})O_3$ (BBMN) ceramics were not sintered below $900^{\circ}C$. However, when CuO was added to the BBMN ceramic, it was sintered even at $850^{\circ}C$. The amount of the $Ba_2B_2O_5$ second phase decreased with the addition of CuO. Therefore, the CuO additive is considered to react with the $B_2O_3$ inhibiting the reaction between $B_2O_3$ and BaO. Moreover, it is suggested that the solid solution of CuO and $B_2O_3$ might be responsible for the decrease of the sintering temperature of the specimens. A dense microstructure without pores was developed with the addition of a small amount of CuO. However, a porous microstructure with large pores was formed when a large amount of CuO was added. The bulk density the dielectric constant $({\varepsilon}_r)$ and the Q-value increased with the addition of CuO but they decreased when a large amount of CuO was added. The variations of those properties are closely related to the variation of the microstructure. The excellent microwave dielectric properties of Qxf=21500 GHz, ${\varepsilon}_r=31$ and temperature coefficient of resonance frequency$({\tau}_f)=21.3\;ppm/^{\circ}C$ were obtained for the $Ba(Mg_{1/3}Nb_{2/3})O_3+2.0\;mol%B_2O_3+10.0$ mol%CuO ceramic sintered at $875^{\circ}C$ for 2h.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.3 s.32
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• pp.17-22
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• 2004

The microwave dielectric properties of $CaZrO_3$ ceramics with addition of $CaTiO_3$ were studied. The effect of glass addition on the low-temperature sintering and microwave dielectric properties of $CaZrO_3-CaTiO_3$ ceramics were also evaluated to develop the materials for functional substrates of low-temperature co-fired ceramics. When $10-20 wt\%$ of lithium borosilicate glass was added, the sintering temperature of the $CaZrO_3-CaTiO_3$ ceramics decreased from $1450^{\circ}C$ to below $900^{\circ}C$. As the $T_f$ of glass frits and $CaZrO_3$ are slightly negative and that of $CaTiO_3$ is significantly positive, zero $T_f$ could be realized by mixing an appropriate amount of $CaTiO_3$ with $CaZrO_3$. The $CaZrO_3-CaTiO_3$ ceramics sintered at $875^{\circ}C$ with $15wt\%$ glass frits showed the relative density of $98\%$, permittivity of 23, quality factor of 2500 GHz, and temperature coefficient of resonant frequency of $ -3 ppm/^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.39 no.9
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• pp.890-895
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• 2002

Effect of the sintering time on the microwave dielectric properties of the layered Functionally Graded Materials(FGMs) of the Mg0.93Ca0.07TiO3(MCT) with (Ca0.3Li0.14Sm0.42)TiO3(CLST) ceramics was investigated. The dielectric constant of layered FGMs specimens showed a nearly constant value and did not change significantly with sintering time. The quality factor, however, was affected by the relative density and thermal stress developed in each dielectric layer. With an increase of the relative density and the decrease of the induced thermal stresses, quality factor of the layered FGMs specimens increased and the quality factor was incluenced sensitively by the change of compressive stress developed in MCT layers which had a lower thermal expansion coefficient than that of CLST. For the layered FGMs specimen sintered at 1300$^{\circ}C$ for 9h, the compressive stress developed in MCT layer showed the maximum value, which, in turn, the quality factor of the specimen was the minimum value.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.6
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• pp.356-360
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• 2017

We investigated the phase evolution, microstructure, and microwave dielectric properties of Na- and Zr-doped $Ba(Mg_{0.5}W_{0.5})O_3$ [i.e., ($Ba_{1-2x}Na_{2x})(Mg_{0.5-x}Zr_xW_{0.5})O_3$] ceramics. $BaWO_4$ as a secondary phase was observed in all compositions, and it increased as the dopant concentration increased. All specimens revealed a dense microstructure. For the composition of x=0.01, polyhedral grains were observed. As the dopant concentration increased, the densification and the grain growth were promoted by a liquid phase. The quality factor($Q{\times}f_0$) decreased remarkably, whereas the dielectric constant (${\varepsilon}_r$) tended to decrease as the dopant concentration increased. The dielectric constant, quality factor, and temperature coefficient of the resonant frequency of the composition of x=0.01 sintered at $1,700^{\circ}C$ for 1 h were 18.6, 216,275 GHz, and $-22.0ppm/^{\circ}C$, respectively.

• Korean Journal of Materials Research
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• v.19 no.10
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• pp.550-554
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• 2009

Unreported dielectrics based on the binary system of MgO-SiO$_2$ were investigated as potential candidates for microwave dielectric applications, particularly those demanding a high fired density and high quality factors. Extensive dielectric compositions having different molar ratios of MgO to SiO$_2$, such as 2:1, 3:1, 4:1, and 5:1, were prepared by conventional solid state reactions between MgO and SiO$_2$. 1 mol% of V$_2$O$_5$ was added to aid sintering for improved densification. The dielectric compositions were found to consist of two distinguishable phases of Mg$_2$SiO$_4$ and MgO beyond the 2:1 compositional ratio, which determined the final physical and dielectric properties of the corresponding composite samples. The increase of the ratio of MgO to SiO$_2$ tended to improve fired density and quality factor (Q) without increasing grain size. As a promising composition, the 5MgO.SiO$_2$ sample sintered at 1400 $^{\circ}C$ exhibited a low dielectric constant of 7.9 and a high Q $\times$ f (frequency) value of $\sim$99,600 at 13.7 GHz.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.7-14
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• 1999

TiZrB2 solid solution was synthesized using fine powders of Ti, Zr and B by SHS microwave process. The characterization of the synthesized powder and sintered bodies ws investigated. The combustion temperature and rate were increased with increasing the mole ratio of Zr in temperature profile, and showed the maximum combustion temperature and velocity values of 285$0^{\circ}C$ and 14.6mm/sec in Ti0.2Zr0.8B2 composition. Phase separation has been occured into a composite with TiB2 and ZrB2 phases from TiZrB2 solid solution, which was hot pressed sintering at 30 MPa for an hour at 190$0^{\circ}C$. At the composition of Ti0.8Zr0.2B2 the best properties has been obtained in relative density, bending strength, fracture toughness and hardness, with 99%, 680 MPa, 7.3MPa.m1/2 and 2750 Kg/$\textrm{mm}^2$ respectively.

• Journal of the Korean Ceramic Society
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• v.52 no.3
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• pp.215-220
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• 2015

Phase evolution, microstructure, and microwave dielectric properties of $Li_2O$ and $Al_2O_3$ doped $Zn_{1.9}Si_{1.05}O_4$, i.e., $Zn_{1.9-2x}Li_xAl_x-Si_{1.05}O_4$, ceramics (x = 0.02 ~ 0.10) were investigated. The ceramics were densified by $SiO_2$-rich liquid phase composed of the Li-Al-Si-O system, indicating that doped Li and Al contributed to the formation of the liquid. As the secondary phase, ${\beta}$-spodumene solid solution with the composition of $LiAlSi_3O_8$ was precipitated from the liquid during the cooling process. The dense ceramics were obtained for the specimens of $$x{\geq_-}0.06$$ showing the rapid densification above $1000^{\circ}C$, implying that a certain amount of liquid is necessary to densify. The specimen of x = 0.06 sintered at $1050^{\circ}C$ exhibited good microwave dielectric properties; the dielectric constant and the quality factor ($Q{\times}f_0$) were 6.4 and 11,213 GHz, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.9
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• pp.788-793
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• 2002

The glass-electroceramics were composed of glass composition(CaO, $SiO_2$, $B_2$ $O_3$) and electroceramic composition(BaO, N $d_2$ $O_3$, B $i_2$ $O_3$ and Ti $O_2$) Their dielectric properties have been investigated as a function of sintering temperature and glass contents. In the ceramics composed of 0.16BaO-0.15(N $d_{0.87}$,B $i_{0.13}$)$_2$ $O_3$-0.69Ti $O_2$with glass ［EG-2782］ 3wt% addition and sintered at 108$0^{\circ}C$ for 2h, we could obtain microwave properties of dielectric constant $\varepsilon$$_{r}$ = 80.1, quality factor Q $\times$f = 810(at 3.5 GHz) and temperature coefficient of resonant frequency $\tau$$_{f}$ = -1.3 ［ppm/$^{\circ}C$］. These experimental results show that dielectric constant and temperature coefficient of resonant frequency could be estimated by empirical equations involving the rule of mixture.e.