• The Korean Journal of Ceramics
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• v.5 no.2
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• pp.189-194
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• 1999

Crystallization of glasses in the system (Ca, Sr, Ba)$O-Al_2O_3-B_2O_3-SiO_2-TiO_2$ and dielectric properties of crystallized glasses were investigated. As increasing B2O3 content and decreasing SiO2 content in the glass, the major crystalline phase changed from $(Sr, Ba)_2TiSi_2O_8$ to (Ca, Sr, Ba)TiO3, the dielectric constant of crystallized glasses increased and the Temperature Coefficient of Capacitance (TCC) changed to negative. The dielectric constant and TCC was estimated for (Sr, Ba)2TiSi2O8 phase as 18 and -440 $ppm/^{\circ}C$, respectively and for (Ca, Sr, Ba)TiO3 phase as 307 and -1900 $ppm/^{\circ}C$, respectively. The dielectric properties of (Ca, Sr, Ba)TiO3 phase (in this study) were similar to those of (Ca, Ba) TiO_3 solid-solution^12)$, but $(Sr, Ba)_2TiSi_2O_8$ phase (in this study) and $Sr_2TiSi_2O_\;8^4$ showed the different properties.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.5
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• pp.422-426
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• 2006

[ $Sr_xCa_{(1-x)}TiO_3$ ] red phosphors doped with Pr(0.13 mol%) and Al(0.23 mol%) were synthesized by solid state reaction method. Change of crystal structure occurred in $Sr_xCa_{(1-x)}TiO_3:Pr,Al$ phosphors with increasing value of x. Green and red luminescence were observed from $SrTiO_3:Pr,Al$ phosphors at low temperature. However, only red luminescence in the case of $CaTiO_3:Pr,Al$ phosphors was measured at low temperature. The main cause of green luminescence was explained by the bandgap reduction.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.7
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• pp.344-348
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• 2006

The effect of x on microwave dielectric properties of the $(1-x)Mg_4Ta_2O_9-x(TiO_2,\;CaTiO_3,\;SrTiO_3)$ ceramics for microwave components were investigated. All spcecimens prepared by the conventional mixed oxied method and sintered at $1450^{\circ}C$. Microwave dielectric properties of the $(1-x)Mg_4Ta_2O_9-xTiO_2$ ceramics were influenced by $MgTi_2O_5$ phase. Also the microwave dielectric properties of the $(1-x)Mg_4Ta_2O_9-x(TiO_2,\;CaTiO_3,\;SrTiO_3)$ ceramics were dominated with an addition of $CaTiO_3\;and\;SrTiO_3$. The dielectric constant $(\varepsilon_r)$, quality factor $(Q{\times}f_r)$ and temperature coefficient of the resonant frequency $(TCRF,\;\tau_f)$ of the $(1-x)Mg_4Ta_2O_9-x(TiO_2,\;CaTiO_3,\;SrTiO_3)$ ceramics were $12.96\sim70.98,\;5,132\sim186,410GHZ$ and $-35.82\sim+75.96ppm/^{\circ}C$, respectively, and depend on x and addition materials.

• Journal of the Korean Ceramic Society
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• v.43 no.5 s.288
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• pp.284-292
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• 2006

$MgTiO_3{\cdot}CaTiO_3{\cdot}SrTiO_3$ system ceramics (MCST) were synthesized to study the effect of Ca addition amount and Sr substitution on temperature coefficient of resonance sequency. Temperature coefficient of resonance frequency was slightly increased by small amount ($i.e.{\sim}5%$) of Sr substitution. In case of 50% to 75% addition amount of $MgTiO_3$, decrease of quality factor was not observed with increasing dielectric constant.

• Korean Journal of Materials Research
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• v.2 no.4
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• pp.248-256
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• 1992

This paper has reviewed some of the basic principles that underlie the field of defect chemistry in simple ATi$O_3$(A=Ca, Sr, Ba) perovskites. Frenkel defects in perovskite structure is very much unlikely, and Schottky defects and intrinsic electronic defects in undoped materials are negligibly small compared with background acceptor impurities. The electrical properties of perovskite ceramics are dependent on the aliovalent impurities. Since perovskite structure is a ternary system, the stoiohiometry between cations as well as cation-anion ratio will affect defect structure and electrical properties. BaTi$O_3$and SrTi$O_3$show a limited deviation from the cation stoichiometry while CaTi$O_3$has significant excess CaO and Ti$O_2$solubility.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.597-600
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• 2002

Electrical properties of $\{(Sr_xCa_{1-x})_{0.95-y-z}Bi_2Pb_{0.05+y}\})Ti_{1.02}O_3$ ceramic were studied as a function of Sr/Ca ratio and Bi, Pb contents. Dielectric properties of specimens with different x, y, z values were explained in terms of ionic polarizability with Molecular Additionally Rules and Clausius-Mosotti equation. For the composition of $\{(Sr_{0.62}Ca_{0.38})_{0.90}Bi_{0.01}Pb_{0.09}\})Ti_{1.02}O_3$ and $\{(Sr_{0.62}Ca_{0.38})_{0.905}Bi_{0.015}Pb_{0.08}\})Ti_{1.02}O_3$, dielectric constant$({\varepsilon}_r)$, quality factor(Q) and temperature coefficient(TC) were 389, 3048, -1490 and 394, 1869, -1340 at 1MHz, respectively.

• Journal of the Korean Ceramic Society
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• v.34 no.2
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• pp.123-130
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• 1997

In this study, (Sr.Pb.Ca)TiO3-Bi2O3.3TiO2(SPCT) systems were investigated to develop a new material which has a high dielectric constant, a low dielectric loss and a small TCC(Temperature Coefficient of Capa-citance), and are suitable for high voltage applications as a function of the additions of Bi2O3.3TiO2 from 5 mol.% to 9 mol.%. The result obtained from our investigation showed that up to 6 mol.% Bi2O3.3TiO ad-dition the dielectric constant increased and it deteriorated at higher concentrations with increasing amount of the acicular grains. As a result of some dopants (SiO2, Nb2O3, MnO2) addition to SPCT, the specimens with MnO2 showed good dielectric properties. The dielectric constant decreased, but the TCC was improved with the addition of MnO2 from 0.15 wt.% to 0.45 wt. %.

• Journal of the Korean Ceramic Society
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• v.38 no.2
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• pp.107-111
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• 2001

Sr$_{(1-x)}$Ca$_{x}$TiO$_3$: Pr$^{3+}$ , Ga$^{3+}$ (0$\leq$x$\leq$1) 형광체의 여기 및 발광 스펙트럼과 분광 반사율을 조사하여 발광 메커니즘을 규명하고자 하였다. 발광 스펙트럼에서는 611~614nm 사이에서 peak을 가지는 하나의 적색 발광 밴드가 관찰되었으며, 조성에 따라 발광밴드의 모양이 달랐다. 이는 조성에 따른 모체의 결정 구조 변화 때문으로 생각된다. 여기 스펙트럼 끝단과 분광 반사율 스펙트럼의 흡수단은 서로 일치하였으며, 이 결과로부터 모체에 흡수된 에너지가 Pr$^{3+}$ 에 전달되어 적색광을 방출하는 것이 주된 메커니즘으로 생각된다. 한편 120$0^{\circ}C$에서 4시간동안 열처리하여 합성한 Sr$_{0.4}$Ca$_{0.6}$TiO$_3$:(0.1 mol%)Pr$^{3+}$ , (0.2 mol%)Ga$^{3+}$ 는 우수한 색순도와 휘도를 나타내었다.다.

• Journal of the Korean Ceramic Society
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• v.28 no.9
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• pp.689-695
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• 1991

Dielectric properties of Ba1-$\chi$Sr$\chi$Ti1-yCayO3-y ceramics, where Sr and Ca were doped to Ba-site and Ti-site within the range of 0 x 0.24 and 0 y 0.05, respectively, were investigated. The substitution of Ca for Ti, which maintained the high resistivity of these formulations after sintering in a reducing atmosphere, was confirmed. Ca addition decreased the tetragonality c/a, increased the unit cell volume, and lowered Curie temperature, which were attributed to the occupancy of Ca2+ ions on Ti-sites. The lowering of Curie temperature by Ca addition was affected by the substitution of Sr for Ba-site; within 2 mol% of Ca, Curie temperature was lowered at a rate of 2$0^{\circ}C$ and 16$^{\circ}C$ per mol% of Ca at x=0 and x=0.08, respectively. Whereas the resistivity of the formulations without Ca was reduced to 107 {{{{ OMEGA }}cm, when sintered at low oxygen partial pressure of 10-9 MPa, the resistivity value higher than 1011 {{{{ OMEGA }}cm was maintained for the formulations containing Ca more than 0.5 mol%. Dielectric loss factor, tan$\delta$, was about 1% for most formulations.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.180-181
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• 2009

$(Ba_{0.6},Sr_{0.3}Ca_{0.1})TiO_3$ powders, which were prepared by sol-gel method using a solution of Ba-acetate, Sr-acetate and Ca-acetate and Ti iso-propoxide, $(Ba_{0.6},Sr_{0.3}Ca_{0.1})TiO_3$ array thick films doped with 0.1 mol% $MnCO_3$ and $Yb_2O_3$ (0.1~0.7 mol%) were fabricated by the screen printing method on the alumina substrate. And the structural and electrical properties as a function of $Yb_2O_3$ amount were investigated. The thickness of all (Ba,Sr,Ca)$TiO_3$ thick films was approximately 60mm. The Curie temperature of doped with 0.1 mol% $Yb_2O_3$ specimen was $45^{\circ}C$, and the dielectric constant and at this temperature was 1062.