• Journal of the Korean Ceramic Society
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• v.24 no.6
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• pp.579-585
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• 1987

The effects of flux KCl and dopant Nb2O5 on the PTCR characteristics of BaTiO3 prepared by molten salt synthesis method have been investigated. As the amount of dopant Nb2O5 is over the solubility limit in BaTiO3, the room-temperature resistivity increases, and the PTCR effect and the grain size decrease. The variation of the amount of flux KCl slightly influences on the room-temperature resistivity, PTCR effect and grain size in Nb2O5 doped BaTiO3, but BaTiO3 ceramics prepared by the method of molten salt synthesis show larger PTCR effect than those of conventional calcining of mixed oxides.

• Korean Journal of Crystallography
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• v.17 no.1
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• pp.24-32
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• 2006

The microwave dielectric properties of $Zn_3Nb_2O_8\;with\;V_2O_5$ addition were investigated. The addition of $V_2O_5$ enhanced the sinterability of $Zn_3Nb_2O_8$, which resulted in high density of $Zn_3Nb_2O_8$ ceramic greater than 95% of the theoretical value when sintered at $900^{\circ}C$ for 4 hours. X-ray diffraction analysis of sintered $Zn_3Nb_2O_8$ ceramic showed no second phase with $V_2O_5$ addition. Dielectric permittivity(${\varepsilon}_r$) and quality factor($Q{\times}f$) varied with both density at different sintering temperature and $V_2O_5$ addition. Dielectric permittivity, quality factor and temperature coefficient($T_{cf}$) of the two mole of $V_2O_5\;added\;Zn_3Nb_2O_8$ that was sintered at $900^{\circ}C$ were 21.4, 40,000, $-54ppm/^{\circ}C$, respectively.

• Bulletin of the Korean Chemical Society
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• v.27 no.6
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• pp.853-856
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• 2006

Dion-Jacobson phases $CsCa_2Nb_2FeO_9$ and $CsCa_2Nb_2AlO_9$ were reinvestigated by the Rietveld analysis of powder X-ray diffraction (XRD) method, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). These nominal compounds, previously known as the oxygen-deficient layered perovskites with the sequences of $NbO_6-MO_4-NbO_6$ in tripled slab, in fact, were mixed phases of n = 3 Dion-Jacobson phases and impurities such as $Ca_2NbFeO_6$ and $Ca_3Al_2O_6$. The difference of morphology and chemical in-homogeneity between Dion-Jacobson phases and impurities could be clearly identified by scanning electron microscopy with energy-dispersive X-ray spectroscopy. The chemical composition of $CsCa_2Nb_2FeO_9$ was calculated into $Cs_{0.59}Ca_{2.64}Nb_{2.92}Fe_{0.81}$ in small agglomerate crystals and $Cs_{0.95}Ca_{1.97}Nb_{3.08}Fe_{0.15}$ in long plate-like crystals.

• Journal of the Korean Ceramic Society
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• v.25 no.6
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• pp.639-644
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• 1988

The physical and dielectric properties of complex perovskite compound Sr(Mg1/3Nb1/3)O3-Ba(Mg1/3Nb2/3)O3-Ba(Mg1/3Ta2/3)O3(BMT) system were investigated as a function of composition. As the mole ratio of BMN was increased, lattice parameter ratio c/a was slightly increased, and density was increased in SMN-BMN system. However, in BMN-BMT system, lattice parameter ratio c/a and density were decreased with increasing the mole ratio of BMN. Dielectric constant, dielectric loss at $25^{\circ}C$ and 100kHz, and temperature coefficient of resonant frequency, the dependence of temperature in capacitance were increased with increasing the mole ratio of BMN in SMN-BMN-BMT system. These result can be explained according to the degree of order=disorder and dielectric constant.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.44 no.5
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• pp.644-648
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• 1995

Transparent xBa(La$_{1}$2/Nb$_{1}$2/)O$_{3}$-(1-x)Pb(Zr, Ti)O$_{3}$ (x=8.5, 9.0[mol.%], Zr/Ti=70/30~40/60) ceramics were fabricated by the two-stage sintering method, the electrooptic properties were investigated with Ba(La$_{1}$2/Nb$_{1}$2/)O$_{3}$ content and Zr/Ti composition ratio. Decreasing the Zr/Ti ratio, the electrooptic property was changed from a quadratic electrooptic effect to a linear electrooptic effcet. In the BLN-PZT 9.0/50/50 specimen having the tetragonal structure, the linear electrooptic coefficient had the highest value of 6.01*10$^{-10}$ [m/V] and in the BLN-PZT 9.0/55/45 specimen which located near the MPB region, the quadratic electrooptic coefficient had the highest value of 10.53*10$^{-16}$ [m$^{2}$/V$^{2}$].

• Journal of the Korean Ceramic Society
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• v.39 no.10
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• pp.977-980
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• 2002

Using the micro-pulling down method, $Nd_2O_3$ doped crack-free stoichiometric $LiNbO_3$ single crystals were grown in 1 mm diameter and 30∼35 mm length. The homogeneous distributions of $Nd_2O_3$ concentration were confirmed by the electron probe micro analysis. The absorption and photoluminescence spectra were measured with respect to the $Nd_2O_3$ doping.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.44 no.8
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• pp.1068-1074
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• 1995

Effect of (Zn$_{1}$3/Nb$_{2}$3/) $O_{2}$ addition on the phase changes and microwave dielectric properties of BaTi $O_{3}$-3Ti $O_{2}$ ceramics were investigated. Addition of (Zn$_{1}$3/Nb$_{2}$3/) $O_{2}$ to BaTi $O_{3}$-3Ti $O_{2}$ resulted in the formation of Ba $Ti_{4}$$O_{9}$, $Ba_{2}$ $Ti_{9}$ $O_{20}$, Ba(Zn$_{1}$3/Nb$_{2}$3/) $O_{3}$, and Ti $O_{2}$ phases. Ba $Ti_{4}$$O_{9}$ phase was gradually transformed to $Ba_{2}$ $Ti_{9}$ $O_{20}$. This was identified by XRD and microstructure. As the Ba $Ti_{4}$$O_{9}$ phase transformed to $Ba_{2}$ $Ti_{9}$ $O_{20}$ phase, the dielectric constant increased to 37.5. Q*f$_{o}$ value was 40000 at x=0.04, and the temperature coefficient of resonant frequency was +10ppm/.deg. C.C.. C.C.

• The Korean Journal of Ceramics
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• v.6 no.3
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• pp.272-275
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• 2000

Starting from the stoichiometric composition of $K_2$CO$_3$: Li$_2$CO$_3$: Nb$_2$O$_5$=3 : 2 : 5 with the mole ratio, $K_3$LiNb$_6$O$_17$ 17/ single crystals were grown using the Czochralski method. Although the starting melt composition corresponds to the $K_3$Li$_2$Nb$_5$O$_15$ crystals, the chemical composition of the as grown crystals appears to be $K_2.95$Li$_1.33$Nb$_6.17$O$_17$ or $K_2.60$Li$_1.17$Nb$_{5.44}$ 5.44/O$_{15}$ which relatively contain fewer Li ions than $K_3$Li$_2$Nb$_5$O$_15$ crystals. We investigated the influence of the deficiency of the Li ions in the tetragonal tungsten bronze structure through the measurements of DE loop, temperature dependent dielectric constant, differential thermal analysis and temperature dependent X-ray diffraction pattern.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.2
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• pp.121-128
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• 1996

The optimum conditons were experimentally established for the powder synthesis and sintering of the feed-rods for $LiNbO_3$ crystal growth by a floating zone method. At the lower synthesis temperatures(700, $ 800^{\circ}C$) the minor amounts of $Li_2CO_3$ and $Nb_2O_5$ were present in the synthesized $LiNbO_3$ powder and at the higher temperature the particle size increased which is not favorable for the sintering process for the feed-rods. $LiNbO_3$ powder synthesized at $950^{\circ}C$ for 12 hours was found to be the best because it contains only the$LiNbO_3$ phase with the small particle size and uniform particle size distribution. As the sintering temperature and the soaking time increase, the sintered feed-rods exhibited the higher sintered density and grain growth phenomena. The $LiNbO_3$ feed rods sintering at $1100^{\circ}C$ for 2 hours were found to have the best microstructure for the precursor feed-rods of the floating zone crystal growth because of their higher density, small grain size and uniform particle size distribution. As the sintering temperature and the soaking time increase, the sintered feed-rods exhibited the higher sintered density and grain growth phenomena. The $LiNbO_3$ feed rods sintering at $1100^{\circ}C$ for 2 hours were found to have the best microstructure for the precursor feed-rods of the floating zone crystal growth because of their density, small grain size and uniform grain size distribution.

• Proceedings of the Optical Society of Korea Conference
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• 1989.02a
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• pp.222-224
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• 1989

A new fabrication method of proton-diffused LiNbO3 channel waveguides with self-aligned SiO2-Cladding structures are reported, which provides easy control of mode pattern shapes and sizes.