• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.5
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• pp.217-222
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• 2007

Microwave dielectric properties of $(1-x)CaWO_4-xYNbO_4$ ceramics have been investigated as a function of $YNbO_4$ content($0.05{\leq}x{\leq}0.4$). A single phase with tetragonal scheelite structure was obtained up to x=0.10 and then the secondary phase with fergusonite structure was increased. With the increase of $YNbO_4$ content, apparent densities of the specimens were decreased. This results were due to the lower theoretical density of $YNbO_4(5.581g/cm^3)$ than that of $CaWO_4(6.117g/cm^3)$. Dielectric constant(K) and quality factor(Qf) were decreased with $YNbO_4$ content which could be attribute to the decrease of density and the increase of secondary phase. Temperature coefficient of resonant frequency (TCF) of the specimens with the $YNbO_4$ content was depended on dielectric mixing rule.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1993.05a
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• pp.11-14
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• 1993

$BaO-TiO_2$ ceramics ($BaO:TiO_2$=18.2:81.8[mol.%]) were fabricated by mixed-oxide method. Microwave dielectric properties were investigated with sintering temperature and annealing time. Increasing the sintering temperature, the sintered density was decreased. At the sintering temperature of 1400$[^{\circ}C]$, dielectric constant, quality factor and temperature coefficient of resonant frequency had a good values of 35.03, 5690, -4.433$[ppm/^{\circ}C]$, respectively. Increasing the annealing time, dielectric constant and quality factor were increased and temperature coefficient of resonant frequency was decreased.

• Proceedings of the KIEE Conference
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• 1993.11a
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• pp.185-187
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• 1993

0.15BaO-$0.15Sm_2O_3-0.7TiO_2$, ceramics were fabricated by mixed-oxide method. Microwave dielectric properties were investigated with sintering temperature and annealing time. In the specimen sintered at 1350[$^{\circ}C$], dielectric constant, quality factor and temperature coefficient of resonant frequency had a good values of 80.19, 2006 (at 4.6851[GHz]), -27.54[ppm/$^{\circ}C$], respectively. Increasing the annealing time, dielectric constant was almost constant and quality factor was increased. Temperature coefficient of resonant frequency was minimum value (-1.28[ppm/$^{\circ}C$]) at 4 [hr] annealed.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1355-1356
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• 2006

The microwave dielectric properties of the $Ba_{5}Ta_{4}O_{15}$ ceramics with sintering temperature were investigated. All sample of the $Ba_{5}Ta_{4}O_{15}$ ceramics prepared by conventional mixed oxide method and sintered at $1450^{\circ}C{\sim}1575^{\circ}C$. Porosity of the $Ba_{5}Ta_{4}O_{15}$ ceramics was reduced with increasing sintering temperature. The bulk density, dielectric constant and Qualify factor increased with increasing sintering temperature. In the case of $Ba_{5}Ta_{4}O_{15}$ ceramics sintered at $1550^{\circ}C$, The bulk density, dielectric constant and quality factor were $7.31g/cm^2$ and 27.4, 30,635GHz, respectively.

• Korean Journal of Crystallography
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• v.11 no.4
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• pp.195-199
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• 2000

Ceramics based on CaTiO₃-NdAlO₃ solid solutions were synthesized in order to study their dielectric microwave properties. Microstructural analysis was performed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) using different analytical methods such as energy-dispersive X-ray spectroscopy (EDXS). It was observed that the heating conditions during sintering and cooling strongly affect the microstructural development of CaTiO₃-NdAlO₃-based ceramics. Various types and concentrations of structural defects were identified, for example, dislocations, twins and/or antiphase boundaries. all such defects resulted in a degradation of the dielectric microwave properties, in particular the quality factor Q. Dielectric properties of CaTiO₃-NdAlO₃-based ceramics can be improved by an appropriate thermal treatment of ceramics which results in a decrease in the concentrations of the identified microstructural defects.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.1
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• pp.30-37
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• 2005

The microwave dielectric properties and their related structural characteristics in solid solutions of (1-$\chi$) Ba($Mg_{1/3}$Nb$_{2/3}$) $O_3$-$\chi$La(Mg$_{2/3}$Nb$_{1}$3) $O_3$(BLMN) have been investigated by measuring the dielectric constant($\varepsilon$r), Q value and temperature coefficient of resonant frequency($\tau$f) and by observing the crystal structure using high resolution transmission electron microscopy (HRTEM). Microwave dielectric properties showed characteristic features for specific composition. Dielectric constant($\varepsilon$$_{r}$) showed maximum value at the composition which corresponds to the phase boundary between 1 : 2 ordered and 1 : 1 ordered structure. The increase in $\varepsilon$$_{r}$ may be caused by the rattling of ions by incorporating smaller ions and the disordered structure. The variation of temperature coefficient of resonant frequency($\tau$$_{f}$) was investigated in terms of oxygen octahedra tilting.dra tilting.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.314-314
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• 2008

The low temperature sintering and the dielectric properties of $Al_2O_3/SiO_2$-zinc borosilicate glass composites were investigated in the view of the application for LTCC. When the sintering was conducted at $900^{\circ}C$ $ZnAl_2O_4$ and $ZnB_2O_4$ compounds formed at the $Al_2O_3$-rich and the $SiO_2$-rich compositions, respectively. The reaction between ZBS glass and $Al_2O_3/SiO_2$ caused the formation of these compounds. The $Al_2O_3/SiO_2$ ratio affected the dielectric properties. The excellent dielectric properties, i.e., Q$\times$f value= 40,000 GHz and ${\varepsilon}_r$=4.5, were obtained in the $Al_2O_3/SiO_2$-ZBS glass system and fabricated the LTCC substrate materials.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.6
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• pp.538-542
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• 2005

The structural and microwave dielectric properties of $0.7Mg_4Ta_2O_9-0.3SrTiO_3$ ceramics with sintering temperature were investigated. All the sample of the $0.7Mg_4Ta_2O_9-0.3SrTiO_3$ ceramics were prepared by conventional miked oxide method and the sintering temperature was $1425\~1500^{\circ}C$. The hexagonal phase of $Mg_4Ta_2O_9$ and the cubic phase of $SrTiO_3$ were coexisted. The porosity of $0.7Mg_4Ta_2O_9-0.3SrTiO_3$ ceramics were reduced with increasing sintering temperature. In the case of $0.7Mg_4Ta_2O_9-0.3SrTiO_3$ ceramics sintered at $1475^{\circ}C$, dielectric constant, quality factor and temperature coefficient of resonant frequency were 14.51, 82,596 GHz and $-3.14\;ppm/^{\circ}C$, respectively.

• Electrical & Electronic Materials
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• v.9 no.4
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• pp.379-384
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• 1996

The microwave dielectric properties of (I-x)CaTiO$_{3}$-xLaAIO$_{3}$ were investigated. The solid solution of (1-x)CaTiO$_{3}$-xLaAIO$_{3}$ had the perovskite structure in the range of all compositions. The crystal system of (1-x)CaTiO$_{3}$-xLaAIO$_{3}$ was transformed to orthorhombic(x.leq.0.4), psudo-cubic(x=0.5), and rhombohedral (x.geq.0.7) in turn, as the amount of LaAIO$_{3}$ increased. The dielectric constant and temperature coefficient of resonant frequency of solid solution were decreased with the content of LaAIO$_{3}$, whereas, the value of Q . f$_{o}$ was increased. The microwave dielectric material having Q . f$_{o}$ = 32, 500, .epsilon.$_{r}$ = 42, and .tau.$_{f}$ = 5 ppm/.deg. C was obtained from the 0.35CaTiO$_{3}$-0.65LaAIO$_{3}$ composition sintered at 1600.deg. C for 4hrs.hrs.hrs.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.268-269
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• 2007

In this study, the structural and microwave dielectric properties of the $Sr_5Nb_4O_{15}$ cation-deficient perovskite ceramics with sintering temperature were investigated. All sample of the $Sr_5Nb_4O_{15}$ ceramics were prepared by the conventional mixed oxide method and sintered at $1350^{\circ}C{\sim}1500^{\circ}C$. The bulk density, dielectric constant and quality factor of the $Sr_5Nb_4O_{15}$ ceramics were increased with increasing sintering temperature. In the case of the $Sr_5Nb_4O_{15}$ ceramics sintered at $1500^{\circ}C$ for 5h, the dielectric constant, quality factor and temperature coefficient of the resonant frequency (TCRF) were 22.35, 16,577GHz, +13.40ppm/$^{\circ}C$, respectively.