• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.4
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• pp.136-142
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• 2022

The crystal structure, grain growth behavior, and dielectric properties of BaTiO₃ have been studied with the addition of Dy₂O₃. The powders were synthesized at ratios of (100-x)BaTiO₃-xDy₂O₃ (mol%, x = 0, 0.5, 1.0, 2.0) by a conventional solid-state synthesis, and the powder compacts were sintered at 1250℃ for 2 hours in air. As the amount of added Dy₂O₃ was increased, the crystal structure of the sintered samples changed from a tetragonal to a pseudo-cubic structure, and the tetragonality decreased. In addition, a secondary phase of Ba₁₂Dy_4.67Ti₈O₃₅ appeared when Dy₂O₃ was added. The average grain size after sintering decreased and abnormal grains appeared as the amount of Dy₂O₃ increased. It can be explained that the grain growth behavior of the Dy₂O₃ added-BaTiO₃ occurs due to the two-dimensional nucleation and growth, and is governed by the interface reaction. Further, the correlation between crystal structure, microstructure, and dielectric properties was discussed.

• Journal of the Korean Ceramic Society
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• v.32 no.11
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• pp.1269-1275
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• 1995

Effects of GeO2 addition on the thermal and structural stabilities of PbO-Bi2O3-Ga2O3 glasses were studied. Thermal stabilities, as assessed by the weighted thermal stability factors [(Tx-Tg)/Tg], increased with GeO2 concentraton from 0.097 to 0.210 with the addition of 20 mol% GeO2. Increasing GeO2 content resulted in the decrease of apparent density, molar volume, refractive index and thermal expansion. On the other hand, IR transmission cut-off (λT=50%) moved from 6.73${\mu}{\textrm}{m}$ for the ternary PbO-Bi2O3-Ga2O3 glass to shorter wavelength side, 5.98${\mu}{\textrm}{m}$ for a glass containing 20mol% GeO2. There were little change with GeO2 content, however, in the activation energies for the viscous flow of approximately 140 kcal/mole within the temperature interval of 300~50$0^{\circ}C$. Addition of GeO2 to PbO-Bi2O3-Ga2O3 glasses enhanced the thermal and structural stabilities significantly at the expense of their infrared transmittance. An appropriate compsomise between these two opposite trends should be made following the specifications of the final applications.

• Journal of Sensor Science and Technology
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• v.1 no.1
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• pp.93-100
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• 1992

Sinterability, mechanical and electrical properties of yttria-stabilized zirconia(92 mole% $ZrO_{2}$+8 mole% $Y_{2}O_{3}$) doped with 0.5 mole% $SiO_{2}$ and $0{\sim}2.0 mole%{\;}Al_{2}O_{3}$ were studied as a function of $Al_{2}O_{3}$ addition. Sintered density increased with increasing $Al_{2}O_{3}$ addition up to 0.5 mole % but leveled off with further addition. Victors hardness is proportional to sintered density. The specimen with 0.5 mole% $Al_{2}O_{3}$ and 0.5 mole% $SiO_{2}$ exhibited the maximum electrical conductivity and revealed a maximum electromotive force for a given oxygen partial pressure. Experimental voltage curve of this oxygen sensor take on a sharper, more steplike transition at the stoichiometric A/F ratio than those of other commercial oxygen sensors.

• Journal of the Korean Ceramic Society
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• v.37 no.2
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• pp.186-193
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• 2000

Effects of 1.0 mol% CoO addition on sintering and the electrical properties of ZnO-Bi2O3-Sb2O3(ZBS) varistor system with 3.0 mol% co-addition of Sb2O3 and Bi2O3 at various Sb/Bi ratio (0.5, 1.0, and 2.0) were investigated. Cobalt had little influence on the liquid-phase formation and the pyrochlore decomposition temepratures of ZBS, while densification was mainly dependent on Sb/Bi ratio: when Sb/Bi=0.5, excess Bi2O3 irrelevant to the formation of pyrochore(Zn2Sb3Bi3O14) forms eutectic liquid at ~75$0^{\circ}C$ which promotes densification and grain growth; with Sb/Bi=2.0, the second phase Zn7Sb2O12 formed by excess Sb2O3 irrelevant to the formation of the pyrochlore retards densification up to ~100$0^{\circ}C$. These phases caused the coarsening and uneven distribution of the second phase particles on the grain boundaries of ZnO above the pyrochlore decomposition temperature(~105$0^{\circ}C$), which led to broad size dist-ribution of ZnO; the specimen with Sb/Bi=1.0 showed homogeneous microstructure compared with the others, which enabled improved varistor characteristics. Doping of Co increased the nonlinearity and the potential barrier height of ZBS, which is thought to stem from improved sintering behavior such as homogenized microstructure due to size reduction and even distribution of the second phase and suppressed volatility of Bi2O3, as well as the improvement in the potential barrier structure via increased donor and interface electron trap densities.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.112-116
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• 2002

The $0.95MgTiO_3-0.05SrTiO_3$ ceramics with $V_2O_5$(10wt%) were prepared by the conventional mixed oxide method. The structural properties were investigated with sintering temperatue by XRD. According to the X-ray diffraction pattern of the $0.95MgTiO_3-0.05SrTiO_3$ ceramics with $V_2O_5$(10wt%), the ilmenite $MgTiO_3$ and perovskite $SrTiO_3$ structures were coexisted and secondary phase $MgTi_2O_5$ were appeared. In the case of $0.95MgTiO_3-0.05SrTiO_3$ ceramics with $V_2O_5$(10wt%), dielectric constant, quality factor and temperature coefficient of resonant frequency were 15.84~18.28, 12627~23138GHz, -21.414~1.568$ppm/^{\circ}C$, respectively.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.30-35
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• 1999

For dolomite clinkers used as stamp materials, the corrostion behavior of those by slag was inverstigated between 1550$^{\circ}C$ and 1650$^{\circ}C$. Fe2O3 among slag components was selectively penetrated into the grain boundaries of dolomite clinkers. In hot face, the magnesioferrite was preferentially formed by Fe2O3 component contained in dolomite clinker rather than Fe2O3 of slag. The corrosion steps of dolomite clinkers by slag were found as follows ; (1) The dicalciumferrite was formed by the reaction of the calcia within dolomite clinkers with Fe2O3 of slag. (2) The magnesia within dolomite clinkers reacted with the dicalciumferrite to from magnesioferrite and the residual calcia within dolomite clinkers reacted with the dicalciumferrite to form magnesioferrite and the residual calcia was dissolved into slag. (3) The magnesioferrite was corroded by CaO-SiO2 compounds of slag. With the temperature of slag increased, the magnesioferrite layer in hot face was decreased for dolomite clinker without Fe2O3 while the layer thickness and grain sizes of magnesioferrite was increased for dolomite clinker with Fe2O3.

• Journal of Korean Ophthalmic Optics Society
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• v.7 no.1
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• pp.57-61
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• 2002

Ternary $SrO-B_2O_3-SiO_2$ glasses were fabricated as a function of R(${\equiv}SrO\;mole%/B_2O_3\;mole%$) and K(${\equiv}SiO_2\;mole%/B_2O_3\;mole%$). The structures of these glasses were investigated through Infrared transmittance, vicker's hardness, and refractive index. The results indicated : First, in the infrared transmittance spectra, when R increased, the intensities of the absorption bands around $1200{\sim}1600cm^{-1}$ resulting from the B-O stretching vibration bond in the symmetrical trigonal $BO_3$ units decreased, and these of the absorption bands around $800{\sim}1200cm^{-1}$ caused by the B-O stretching vibration bond of the tetrahedral $BO_4$ units varied. Also, the intensities of the absorption bands for the B-O stretching vibration bond in trigonal $BO_3$ units increased and these of the bands for B-O stretching vibration bond in tetrahedral $BO_4$ units decreased as K increased. Second, the increase and the decrease of vicker's hardness values for these glasses depended on the fraction of $BO_4$ units and it of $BO_3$ units, respectively. The refractive index of these glasses mostly depended on the SrO contents and only slightly depended on the fraction of $BO_4$ and $BO_3{^-}$ units.

• Proceedings of the Materials Research Society of Korea Conference
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• 1994.11a
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• pp.141-141
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• 1994

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.1
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• pp.19-24
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• 2007

The effects of $B_2O_3-SiO_2-R(R;CaO,\;BaO,\;ZnO,\;Bi_2O_3)$ borosilicate glass system on the sintering behavior and microwave dielectric properties of ceramic/glass composites were investigated as functions of modifier, glass addition ($30{\sim}50\;vol%$) and sintering temperature ($500{\sim}900^{\circ}C$ for 2 hrs). The addition of 50 and 45 vol% glass ensured successful sintering below $900^{\circ}C$. Sintering characteristics of the composites were well described in terms of modifier. Borosilicate glass enhanced the reaction with $Al_{2}O_{3}$ to form pores, second phases and liquid phases, which was responsible to component of modifier. Dielectric constant (${\varepsilon}_{r},\;Q{\times}f_{o}$) and temperature coefficient of resonant frequency (${\tau}_{f}$) of the composite with 50 and 45 vol% glass contents($B_{2}O_{3}:SiO_{2}:R=25:10:65$) demonstrated A-CaBS(7.8, 2,560 GHz, -81ppm/$^{\circ}C$), A-BaBs(5.8, 3.130 GHz, -64 ppm/$^{\circ}C$), A-ZnBS(5.7, 17,800 GHz, -21 ppm/$^{\circ}C$), A-BiBs(45 vol% glass in total)(8.3, 2,700 GHz, -45 ppm/$^{\circ}C$) which is applicable to substrate requiring an low dielectric properties.

• Journal of the Korean Ceramic Society
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• v.40 no.5
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• pp.447-454
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• 2003

Samples were prepared by the solid-state reaction method. The nominal composition of the samples was B $i_{1.84}$P $b_{0.34}$S $r_{1.91}$C $a_{2.03}$C $u_{3.06}$ $O_{10+{delta}$ prepared from powder of B $i_2$ $O_3$, PbO, SrC $O_3$, CaC $O_3$, and CuO. They were pulverized, mixed with AgO, A $u_2$ $O_3$and MgO of 50 wt%. Finally, they were sintered at 820 to 85$0^{\circ}C$ in air. The structural characteristics, the microstructure of surface and the critical temperature with respect to the each samples were analyzed by XRD, $T_{c}$, SEM and EDS respectively. It was found that the the critical temperature of the silver oxide additive samples (99.58 K) is higher than those of gold or magnesium oxides additive samples, but all those values are lower than that of pure Bi-2223 phase. The microstructure of surface showed the tendency which the AgO additive samples become more minuteness than A $u_2$ $O_3$ and MgO additive samples.s.samples.s.